Scientific publications

Safety of Medications During Pregnancy and Breastfeeding: Infants of Drug-Addicted Mothers
Karel Allegaert, Tim van Mieghem, and John N. van den Anker
Book chapter in: G. Buonocore et al. (eds.), Neonatology, DOI 10.1007/978-3-319-18159-2_192-1
Any decision on maternal pharmacotherapy should be balanced, comparing maternal and fetal/neonatal outcome to withholding any treatment. This is because there is a relevant body of evidence that uncontrolled maternal conditions also affect fetal outcome. The same holds true for breastfeeding. Drugs are not thoroughly evaluated for use during pregnancy or breastfeeding. Knowledge on safety of drugs exposure during fetal and neonatal (breastfeeding) life is limited.
Pregnancy category classifications for drugs are currently used, but have their limitations. Pregnancy exposure registries to build knowledge have been implemented in the recently revised version of the FDA labelling guidelines (Pregnancy and Lactation Labeling Final Rule). Suggestive indicators of “likely safe during breastfeeding” are (i) drugs commonly administered to infants, (ii) drugs that are not absorbed following oral administration, (iii) not excreted into human milk, and finally (iv) drug considered safe during pregnancy, since fetal exposure is generally longer and more extensive. Aspects of opioids, benzodiazepines, and anti-epileptics use during fetal life or via breastfeeding have been discussed to illustrate the concepts of pregnancy-related clinical pharmacology, followed by a focused discussion on neonatal abstinence syndromes. We hereby aim to provide the practicing clinician with some guidance and sources of information.

Therapeutic efficacy and safety of ACE inhibitors in the hypertensive paediatric population: a review
Evelien Snauwaert, Johan Vande Walle, Pauline De Bruyne
Arch Dis Child. 2016 Sep 28. pii: archdischild-2016-310582. doi: 10.1136/archdischild-2016-310582. [Epub ahead of print] Link
Since 1997, strong incentives have been introduced worldwide to improve access to safe and effective medicines addressing the therapeutic needs of children. ACE inhibitors, the most prescribed antihypertensive drugs in the paediatric population, are one of the prototype drugs targeted by the legislation initiatives. Our purpose in assembling this review is to evaluate and describe the current evidence for the efficacy and safety profile of ACE inhibitors in the paediatric population. The authors made a descriptive review of the literature from 1980 to 2015 using the following search terms: hypertension, child, paediatric, ACE (inhibitors), renin–angiotensin aldosterone system, captopril, lisinopril, enalapril, ramipril and fosinopril. A total of 16 studies evaluating efficacy and safety of ACE inhibitors were included in this review. The included studies demonstrate that ACE inhibitors have the potency to decrease the systolic and/or diastolic blood pressure with an overall favourable safety profile in a short-term period. More importantly, the incentives resulted in an improvement of the overall availability of paediatric labelling, dosing and safety information for ACE inhibitors. However, they failed to fulfil several of paediatric needs: absence of long-term safety data on growth and maturation, absence of commercially available child-friendly formulations and incomplete evaluation of the entire paediatric hypertension population. Additional efforts are needed to close the gap between the availability of drugs that are labelledand indicated for paediatric use and the actual drug usage in children, especially in young children, neonates and children with severe hypertension, renal transplantation or severe renal impairment.

Propofol Dose-Finding to Reach Optimal Effect for (Semi-)Elective Intubation in Neonates
Anne Smits, Liesbeth Thewissen, Alexander Caicedo, Gunnar Naulaers, and Karel Allegaert
J Pediatr. 2016 Sep 2. pii: S0022-3476(16)30651-5.
OBJECTIVE:To define the effective dose for 50% of patients (ED50) of propofol for successful intubation and to determine the rate of successful extubation in those patients with planned intubation, surfactant administration, and immediate extubation (INSURE procedure). In addition, pharmacodynamic effects were assessed.
STUDY DESIGN: Neonates (n = 50) treated with propofol for (semi-)elective endotracheal intubation were stratified in 8 strata by postmenstrual and postnatal age. The first patient in each stratum received an intravenous bolus of 1 mg/kg propofol. Dosing for the next patient was determined using the up-and-down method. A propofol ED50 dose was calculated in each stratum with an effective sample size of at least 6, via the Dixon-Masey method, with simultaneous assessment of clinical scores and continuous vital sign monitoring.
RESULTS: Propofol ED50 values for preterm neonates <10 days of age varied between 0.713 and 1.350 mg/kg. Clinical recovery was not attained at the end of the 21-minute scoring period. Mean arterial blood pressure showed a median decrease between 28.5% and 39.1% from baseline with a brief decrease in peripheral and regional cerebral oxygen saturation. Variability in mean arterial blood pressure area under the curve could not be explained by weight or age.
CONCLUSIONS: Low propofol doses were sufficient to sedate neonates for intubation. Clinical recovery was accompanied by permissive hypotension (no clinical shock and no treatment). The propofol ED50 doses can be administered at induction, with subsequent up-titration if needed, while monitoring blood pressure. They can be used for further dosing optimalization and validation studies.
TRIAL REGISTRATION: NCT01621373; EudraCT: 2012-002648-26.

The amikacin research program: a stepwise approach to validate dosing regimens in neonates
Anne Smits, Aida Kulo, John van den Anker and Karel Allegaert
Expert Opin Drug Metab Toxicol. 2016 Sep 21:1-10. [Epub ahead of print] Link

Introduction: For safe and effective use of antibacterial agents in neonates, specific knowledge on the pharmacokinetics (PK) and its covariates is needed. This necessitates a stepwise approach, including prospective validation.

Areas covered: We describe our approach throughout almost two decades to improve amikacin exposure in neonates. A dosing regimen has been developed and validated using pharmacometrics, considering current weight, postnatal age, perinatal asphyxia, and ibuprofen use. This regimen has been developed based on clinical and therapeutic drug monitoring (TDM) data collected during routine care, and subsequently underwent prospective validation. A similar approach has been scheduled to quantify the impact of hypothermia. Besides plasma observations, datasets on deep compartment PK were also collected. Finally, the available literature on developmental toxicology (hearing, renal) of amikacin is summarized.

Expert opinion: The amikacin model reflects a semi-physiological function for glomerular filtration. Consequently, this model can be used to develop dosing regimens for other aminoglycosides or to validate physiology-based pharmacokinetic models. Future studies should explore safety with incorporation of covariates like pharmacogenetics, biomarkers, and long-term outcomes. This includes a search for mechanisms of developmental toxicity. Following knowledge generation and grading the level of evidence in support of data, dissemination and implementation initiatives are needed.

The Potential Use of Piglets as Human Pediatric Surrogate for Preclinical Pharmacokinetic and Pharmacodynamic Drug Testing
Elke Gasthuys, Tim Vandecasteele, Pauline De Bruyne, Johan Vande Walle, Patrick De Backer, Pieter Cornillie, Mathias Devreese and Siska Croubels1
Curr Pharm Des. 2016;22(26):4069-85.
Pediatric drug research is still substandard, not reaching the same quality level as adult drug research. Despite the efforts made by the Food and Drug Administration and European Medicines Agency to reduce off-label use in children, the lack of clinical studies involving the pediatric population still stands. Pharmacokinetic and pharmacodynamics studies (PK/PD) taking growth and maturation into account are necessary to rationalize dosing strategies in children. Currently, traditional animal models such as rats, mice, dogs and primates are used to conduct pharmacokinetic and pharmacodynamic studies, however age-related trials are rather uncommon. Moreover, these species have several shortcomings as animal models, such as a different physiology and anatomy of the gastrointestinal tract in dogs or the ethical aspects for the use of primates. In contrast, piglets might be potential biomedical pediatric animal models because of the good resemblance with humans, anatomically, physiologically and biochemically. This review summarizes the comparative anatomy and physiology and postnatal development of piglets and infants, focusing on six major topics, namely growth, cardiovascular system, gastrointestinal tract, liver, kidney and integument. Furthermore, the application of piglets as animal model in pediatric PK/PD research is discussed.

Different Vancomycin Immunoassays Contribute to the Variability in Vancomycin Trough Measurements in Neonates
Janko Samardzic, Anne Smits, Isabel Spriet, Ivan Soldatovic, Andrew Atkinson, Milica Bajcetic, John N. Van Den Anker and Karel Allegaert
BioMed Research International, vol. 2016, Article ID 1974972, 4 pages
Substantial interassay variability (up to 20%) has been described for vancomycin immunoassays in adults, but the impact of neonatal matrix is difficult to quantify because of blood volume constraints in neonates. However, we provide circumstantial evidence for a similar extent of variability. Using the same vancomycin dosing regimens and confirming similarity in clinical characteristics, vancomycin trough concentrations measured by PETINIA (2011-2012, = 400) were 20% lower and the mean difference was 1.93mg/L compared to COBAS (2012–2014, = 352) measurements. The impact of vancomycin immunoassays in neonatal matrix was hereby suggested, supporting a switch to more advanced techniques (LC-MS/MS).

All medicines have side effects
Karel Allegaert, Imti Choonara
Arch Dis Child. 2016 Oct;101(10):951-2

A Mechanism to Explain Ototoxicity in Neonates Exposed to Bumetamide: Lessons to Help Improve Future Product Development in Neonates
Karel Allegaert, Amir Lahav, John N. van den Anker
Paediatr Drugs. 2016 Oct;18(5):331-3
The most prominent feature of neonatal clinical pharmacology is huge variability in pharmacokinetics and pharmacodynamics of frequently used medicines due to rapid growth and maturation. This variability is further aggravated by other covariates such as disease characteristics, co-medication or pharmacogenetics. A thorough understanding of developmental changes affecting pharmacokinetics (absorption, distribution, metabolism, elimination) in neonates is essential to provide accurate dose adjustments. While there is increasing knowledge on the impact of these maturational changes on pharmacokinetics, there is currently very limited data on developmental pharmacodynamics [1]. The fact that adverse drug events in neonates are common and may have lifelong consequences, focused pharmacovigilance is urgently needed. Even more, pharmacovigilance should stimulate us to try unveiling the underlying mechanisms of adverse events, and to use this newly acquired knowledge in redesigning the product development approach in neonates.

Changes in Oxygenation Levels Precede Changes in Amplitude of the EEG in Premature Infants
Alexander Caicedo, Liesbeth Thewissen, Anne Smits, Gunnar Naulaers, Karel Allegaert, and Sabine Van Huffel
Book chapter in: Luo et al. (eds.), Oxygen Transport to Tissue XXXVIII, Advances in Experimental Medicine and Biology 923
Brain function is supported by an appropriate balance between the metabolic demand and the supply of nutrients and oxygen. However, the physiological
principles behind the regulation of brain metabolism and demand in premature infants are unknown. Some studies found that changes in hemodynamic variables in this population precede changes in EEG activity; however, these studies only used descriptive statistics. This paper describes the relationship between changes in cerebral oxygenation, assessed by means of near-infrared spectroscopy (NIRS), and changes in EEG, using mathematical methods taken from information dynamics. In a cohort of 35 neonates subjected to sedation by propofol, we quantified the direction of information transfer between brain oxygenation and EEG. The results obtained indicate that, as reported in other studies, changes in NIRS are likely to precede changes in EEG activity.

Pharmacometric Approaches to Personalize Use of Primarily Renally Eliminated Antibiotics in Preterm and Term Neonates.
Wilbaux M, Fuchs A, Samardzic J, Rodieux F, Csajka C, Allegaert K, van den Anker JN, Pfister M
Journal of Clinical Pharmacology. 2016 Aug;56(8):909-35.
Sepsis remains a major cause of mortality and morbidity in neonates, and, as a consequence, antibiotics are the most frequently prescribed drugs in this vulnerable patient population. Growth and dynamic maturation processes during the first weeks of life result in large inter- and intrasubject variability in the pharmacokinetics (PK) and pharmacodynamics (PD) of antibiotics. In this review we (1) summarize the available population PK data and models for primarily renally eliminated antibiotics, (2) discuss quantitative approaches to account for effects of growth and maturation processes on drug exposure and response, (3) evaluate current dose recommendations, and (4) identify opportunities to further optimize and personalize dosing strategies of these antibiotics in preterm and term neonates. Although population PK models have been developed for several of these drugs, exposure-response relationships of primarily renally eliminated antibiotics in these fragile infants are not well understood, monitoring strategies remain inconsistent, and consensus on optimal, personalized dosing of these drugs in these patients is absent. Tailored PK/PD studies and models are useful to better understand relationships between drug exposures and microbiological or clinical outcomes. Pharmacometric modeling and simulation approaches facilitate quantitative evaluation and optimization of treatment strategies. National and international collaborations and platforms are essential to standardize and harmonize not only studies and models but also monitoring and dosing strategies. Simple bedside decision tools assist clinical pharmacologists and neonatologists in their efforts to fine-tune and personalize the use of primarily renally eliminated antibiotics in term and preterm neonates.

Developmental Pharmacology and Therapeutics in Neonatal Medicine
Matic M, de Wildt SN, Elens L, de Hoon JN, Annaert P, Tibboel D, van Schaik RH, Allegaert K.
Therapeutic Drug Monitoring. 2016 Aug;38(4):487-92.
This study determined whether the SLC22A1 [encoding the organic cation transporter 1 (OCT1)] genotype could explain, in addition to the postmenstrual age (referring to gestational plus postnatal age) and CYP2D6 genotype, the tramadol (M) pharmacokinetic variability in early infancy.
Fifty infants, median postmenstrual age 39.5 (interquartile range: 36.8-41.3) weeks, received an i.v. M loading dose (2 mg/kg) followed by a continuous infusion (5-8 mg·kg·24 h). Blood was sampled from 4 to 24 hours after start of the M treatment, which generated 230 observations. M and O-desmethyltramadol (M1) concentrations were measured by high-performance liquid chromatography.
Linear mixed-model analysis illustrated that the SLC22A1/OCT1 genotype was independently associated with a log-transformed M1/M ratio (P = 0.013), with carriers of CONCLUSIONS:
These findings highlight the additional role of SLC22A1/OCT1 genetics in M1 exposure in neonates. They also suggest that OCT1 is already active early after birth, which may have impact on the disposition of other OCT1 substrates in this population.

Developmental Pharmacology and Therapeutics in Neonatal Medicine
Allegaert K, Samardzic J, Bajcetic M, van den Anker JN
Book chapter in Neonatology – A Practical Approach to Neonatal Diseases, 2nd edition (eds: Buonocore G, Bracci R, Weindling M )
Knowledge about the safe and effective use of medicines in neonates has increased substantially but resulted in few label changes. Despite the extent of these drug exposures, newborns remain the last therapeutic orphans. Drugs, initially developed for use in adults, are reshaped and tailored to specific neonatal indications. However, neonatal pharmacotherapy not only mirrors adult pharmacotherapy but should be driven by their own specific needs. This is because both pharmacokinetics (absorption, distribution, metabolism, elimination, concentration-time) and pharmacodynamics (concentration-effect) display extensive maturation in early infancy, reflecting maturational physiology. We describe and illustrate the relevance of these maturational changes. We subsequently focus on specific aspects related to therapeutic drug monitoring, the need for population tailored neonatal formulations (including dose flexibility and excipients), and the difficulties related to the recognition of adverse drug reactions in neonates (how to recognize a signal in the noise).

Adverse drug events in pediatric intensive care are common, but improvement strategies exist and are effective.
Allegaert K
Revista Paulista de Pediatria (English Edition), Available online 25 July 2016

Quantitative clinical pharmacology practice for optimal use of antibiotics during the neonatal period.
Samardzic J, Allegaert K, Wilbaux M, Pfister M, van den Anker JN
Expert Opinion on Drug Metabolism and Toxicology. 2016;12(4):367-75.
For safe and effective neonatal antibiotic therapy, knowledge of the pharmacokinetic parameters of antibacterial agents in neonates is a prerequisite. Fast maturational changes during the neonatal period influence pharmacokinetic and pharmacodynamic parameters and their variability. Consequently, the need for applying quantitative clinical pharmacology and determining optimal drug dosing regimens in neonates has become increasingly recognized.
Modern quantitative approaches, such as pharmacometrics, are increasingly utilized to characterize, understand and predict the pharmacokinetics of a drug and its effect, and to quantify the variability in the neonatal population. Individual factors, called covariates in modeling, are integrated in such approaches to explain inter-individual pharmacokinetic variability. Pharmacometrics has been shown to be a relevant tool to evaluate, optimize and individualize drug dosing regimens.
Challenges for optimal use of antibiotics in neonates can largely be overcome with quantitative clinical pharmacology practice. Clinicians should be aware that there is a next step to support the clinical decision-making based on clinical characteristics and therapeutic drug monitoring, through Bayesian-based modeling and simulation methods. Pharmacometric modeling and simulation approaches permit us to characterize population average, inter-subject and intra-subject variability of pharmacokinetic parameters such as clearance and volume of distribution, and to identify and quantify key factors that influence the pharmacokinetic behavior of antibiotics during the neonatal period.

Children in clinical trials: towards evidence-based pediatric pharmacotherapy using pharmacokinetic-pharmacodynamic modeling.
Brussee JM, Calvier EA, Krekels EH, Välitalo PA, Tibboel D, Allegaert K, Knibbe CA
Expert Review of Clinical Pharmacology. 2016 Jun 27:1-10. [Epub ahead of print] Link
In pediatric pharmacotherapy, many drugs are still used off-label, and their efficacy and safety is not well characterized. Different efficacy and safety profiles in children of varying ages may be anticipated, due to developmental changes occurring across pediatric life.
Beside pharmacokinetic (PK) studies, pharmacodynamic (PD) studies are urgently needed. Validated PKPD models can be used to derive optimal dosing regimens for children of different ages, which can be evaluated in a prospective study before implementation in clinical practice. Strategies should be developed to ensure that formularies update their drug dosing guidelines regularly according to the most recent advances in research, allowing for clinicians to integrate these guidelines in daily practice. Expert commentary: We anticipate a trend towards a systems-level approach in pediatric modeling to optimally use the information gained in pediatric trials. For this approach, properly designed clinical PKPD studies will remain the backbone of pediatric research.

Substitution as a Strategy to Improve Excipient Exposure in Neonates: One Piece of the Puzzle
Allegaert, K., Spriets, I.
Pediatric Drugs, 2016 Jun; 18(3):231–233
This comment refers to the article available at:

Clinical pharmacology of analgosedatives in neonates: ways to improve their safe and effective use
Smits A, van den Anker JN, Allegaert K
Journal of Pharmacy and Pharmacology 2016 Jun; EPub ahead of print.
To propose approaches tailored to the specific needs of neonates, such as structured product development programmes, with the ultimate goal to improve the safe and effective use of analgosedatives in these fragile patients.
Key findings
The feasibility and relevance of a structured product development programme in neonates (optimal study design based on preliminary data; model development; internal, external and prospective evaluation; an individualized dosing regimen; long-term safety; pharmacogenetics) are illustrated for the use of
morphine. Based on changes in clinical practices, similar development plans are in progress for short-acting analgosedatives such as propofol, but are in need of
tailored pharmacodynamic tools to assess and quantify effects. Furthermore, for drugs like paracetamol where there is already sufficient clinical pharmacology
knowledge, attention needs to be given to long-term safety aspects. Finally, new covariates such as pharmacogenetics might further improve neonatal pain management, but clearly need to be integrated with other well-established covariates like age or weight.
Product development programmes for analgosedatives in neonates are needed. These programmes should be tailored to their specific needs (short-acting
sedation, pain relief), should include long-term safety and should incorporate the exploration of newer covariates like pharmacogenetics.

Moral Hazard in Pediatric Drug Research.
Van Hoof W.
The American Journal of Bioethics 2016 Jun; 16(7):54-55
The concept of moral hazard is interesting and useful in the context of pediatric care. It offers a productive way of approaching risk assessment and conflict of interest in surrogate decision making. The ethics of decision making in pediatrics often seem straightforward: The golden rule for parents and caretakers is to act in the best interest of the child. However, real difficulties can arise when assessing what this entails (e.g., considerations about risk/benefit, acceptable harms, quality of life). The added value of the concept of moral hazard as applied by Brunnquell and Michaelson (2016) is that it makes explicit the fact that the decision makers are not the ones primarily affected by the consequences of the decision and can unduly influence pediatric medical care. Moral hazard helps to understand the observation that interests of different parties may not align in surrogate decision-making processes, which inadvertently has an influence on the decisions. In other words, even when parents and caretakers want to make the best possible decision for their child, they may not be able to see the information objectively or they may interpret it differently.

The pathophysiology of monosymptomatic nocturnal enuresis with special emphasis on the circadian rhythm of renal physiology.
Dossche L,Vande Walle J, Van Herzeele C.
Eur J Pediatr. 2016 Jun;175(6):747-54
Nocturnal polyuria in monosymptomatic nocturnal enuresis (MNE) has so far mainly been attributed to a disturbed circadian rhythm of renal water handling. Low vasopressin levels overnight correlate with absent maximal concentrating activity, resulting in an increased nocturnal diuresis with low urinary osmolality. Therefore, treatment with desmopressin is a rational choice. Unfortunately, 20 to 60 % of children with monosymptomatic enuresis are desmopressin-resistant. There is increasing evidence that other disturbed circadian rhythms might play a role in nocturnal polyuria. This review focuses on renal aspects in the pathophysiology of nocturnal polyuria in MNE, with special emphasis on circadian rhythms. Articles related to renal circadian rhythms and enuresis were searched through the PubMed library with the goal of providing a concise review.
Nocturnal polyuria can only partially be explained by blunted circadian rhythm of vasopressin secretion. Other alterations in the intrinsic renal circadian clock system also seem to be involved, especially in desmopressin-resistant enuresis.

Effects of Food and Pharmaceutical Formulation on Desmopressin Pharmacokinetics in Children.
Michelet R, Dossche L, De Bruyne P, Colin P, Boussery K, Vande Walle J, Van Bocxlaer J, Vermeulen A.
Clin Pharmacokinet. 2016 Apr 22. [Epub ahead of print] Link
Desmopressin is used for treatment of nocturnal enuresis in children. In this study, we investigated the pharmacokinetics of two formulations-a tablet and a lyophilisate-in both fasted and fed children.
Previously published data from two studies (one in 22 children aged 6-16 years, and the other in 25 children aged 6-13 years) were analyzed using population pharmacokinetic modeling. A one-compartment model with first-order absorption was fitted to the data. Covariates were selected using a forward selection procedure. The final model was evaluated, and sensitivity analysis was performed to improve future sampling designs. Simulations were subsequently performed to further explore the relative bioavailability of both formulations and the food effect.
The final model described the plasma desmopressin concentrations adequately. The formulation and the fed state were included as covariates on the relative bioavailability. The lyophilisate was, on average, 32.1 % more available than the tablet, and fasted children exhibited an average increase in the relative bioavailability of 101 % in comparison with fed children. Body weight was included as a covariate on distribution volume, using a power function with an exponent of 0.402. Simulations suggested that both the formulation and the food effect were clinically relevant.
Bioequivalence data on two formulations of the same drug in adults cannot be readily extrapolated to children. This was the first study in children suggesting that the two desmopressin formulations are not bioequivalent in children at the currently approved dose levels. Furthermore, the effect of food intake was found to be clinically relevant. Sampling times for a future study were suggested. This sampling design should result in more informative data and consequently generate a more robust model.

Invited review: Clinical research in neonates and infants: Challenges and perspectives
Coppini R, Simons SH, Mugelli A, Allegaert K
Pharmacological Research 2016 Apr 30;108:80-87. [Epub ahead of print] Link
For safe and effective neonatal antibiotic therapy, knowledge of the pharmacokinetic parameters of antibacterial agents in neonates is a prerequisite. Fast maturational changes during the neonatal period influence pharmacokinetic and pharmacodynamic parameters and their variability. Consequently, the need for applying quantitative clinical pharmacology and determining optimal drug dosing regimens in neonates has become increasingly recognized.
Modern quantitative approaches, such as pharmacometrics, are increasingly utilized to characterize, understand and predict the pharmacokinetics of a drug and its effect, and to quantify the variability in the neonatal population. Individual factors, called covariates in modeling, are integrated in such approaches to explain inter-individual pharmacokinetic variability. Pharmacometrics has been shown to be a relevant tool to evaluate, optimize and individualize drug dosing regimens.
Challenges for optimal use of antibiotics in neonates can largely be overcome with quantitative clinical pharmacology practice. Clinicians should be aware that there is a next step to support the clinical decision-making based on clinical characteristics and therapeutic drug monitoring, through Bayesian-based modeling and simulation methods. Pharmacometric modeling and simulation approaches permit us to characterize population average, inter-subject and intra-subject variability of pharmacokinetic parameters such as clearance and volume of distribution, and to identify and quantify key factors that influence the pharmacokinetic behavior of antibiotics during the neonatal period.

Neonatal pain management: still in search for the Holy Grail.
Allegaert K, van den Anker JN
Int J Clin Pharmacol Ther. 2016 Apr 18. [Epub ahead of print] Link
Inadequate pain management but also inappropriate use of analgesics in early infancy has negative effects on neurodevelopmental outcome. As a consequence, neonatal pain management is still in search for the Holy Grail. At best, effective pain management is based on prevention, assessment, and treatment followed by a re-assessment of the pain to determine if additional treatment is still necessary. Unfortunately, epidemiological observations suggest that neonates are undergoing painful procedures very frequently, unveiling the need for effective preventive, non-pharmacological strategies. In addition, assessment is still based on validated, multimodal, but subjective pain assessment tools. Finally, in neonatal intensive care units, there is a shift in clinical practices (e.g., shorter intubation and ventilation), and this necessitates the development and validation of new pharmacological treatment modalities. To illustrate this, a shift in the use of opioids to paracetamol has occurred and short-acting agents (remifentanil, propofol) are more commonly administered to neonates. In addition to these new modalities and as part of a more advanced approach of the developmental pharmacology of analgesics, pharmacogenetics also emerged as a tool for precision medicine in neonates. To assure further improvement of neonatal pain management the integration of pharmacogenetics with the usual covariates like weight, age and/or disease characteristics is needed.

Desmopressin (melt) therapy in children with monosymptomatic nocturnal enuresis and nocturnal polyuria results in improved neuropsychological functioning and sleep.
Van Herzeele C, Dhondt K, Roels SP, Raes A, Hoebeke P, Groen LA, Vande Walle J.
Pediatr Nephrol. 2016 Apr 11. [Epub ahead of print] Link
There is a high comorbidity between nocturnal enuresis, sleep disorders and psychological problems. The aim of this study was to investigate whether a decrease in nocturnal diuresis volume not only improves enuresis but also ameliorates disrupted sleep and (neuro)psychological dysfunction, the major comorbidities of this disorder.
In this open-label, prospective phase IV study, 30 children with monosymptomatic nocturnal enuresis (MNE) underwent standardized video-polysomnographic testing and multi-informant (neuro)psychological testing at baseline and 6 months after the start of desmopressin treatment in the University Hospital Ghent, Belgium. Primary endpoints were the effect on sleep and (neuro)psychological functioning. The secondary endpoint was the change in the first undisturbed sleep period or the time to the first void.
Thirty children aged between 6 and 16 (mean 10.43, standard deviation 3.08) years completed the study. The results demonstrated a significant decrease in periodic limb movements during sleep (PLMS) and a prolonged first undisturbed sleep period. Additionally, (neuro)psychological functioning was improved on several domains.
The study demonstrates that the degree of comorbidity symptoms is at least aggravated by enuresis (and/or high nocturnal diuresis rate) since sleep and (neuro)psychological functioning were significantly ameliorated by treatment of enuresis. These results indicate that enuresis is not such a benign condition as has previously been assumed.

Therapeutic drug monitoring in neonates.
Pauwels S, Allegaert K
Arch Dis Child, April 2016, 101(4):377-81
Therapeutic drug monitoring (TDM) aims to integrate drug measurement results into clinical decision making. The basic rules apply when using TDM in neonates (aminoglycosides, vancomycin, phenobarbital, digoxin), but additional factors should also be taken into account. First, due to both pharmacokinetic variability and non-pharmacokinetic factors, the correlation between dosage and concentration is poor in neonates, but can be overcome with the use of more complex, validated dosing regimens. Second, the time to reach steady state is prolonged, especially when no loading dose is used. Consequently, the timing of TDM sampling is important in this population. Third, the target concentration may be uncertain (vancomycin) or depend on specific factors (phenobarbital during whole body cooling). Finally, because of differences in matrix composition (eg, protein, bilirubin), assay-related inaccuracies may be different in neonates. We anticipate that complex validated dosing regimens, with subsequent TDM sampling and Bayesian forecasting, are the next step in tailoring pharmacotherapy to individual neonates.

Optimizing response to desmopressin in patients with monosymptomatic nocturnal enuresis.
Kamperis K, Van Herzeele C, Rittig S, Vande Walle J.
Pediatr Nephrol. 2016 Apr 12. [Epub ahead of print] Link
Most patients with monosymptomatic nocturnal enuresis can be effectively treated with an enuresis alarm or antidiuretic therapy (desmopressin), depending on the pathophysiology of the condition in the individual patient. Desmopressin is first-line therapy for enuresis caused by nocturnal polyuria, an excessive urine output during the night. However, in a recent study, around one-third of patients thought to be resistant to desmopressin were subsequently treated effectively with desmopressin monotherapy in a specialist centre. The aim of this article is to review best practice in selecting patients for desmopressin treatment, as well as outline eight recommendations for maximizing the chances of treatment success in patients receiving desmopressin. The roles of formulation, dose, timing of administration, food and fluid intake, inter-individual variation in response, body weight, adherence, withdrawal strategies and combination therapies are discussed in light of the most recent research on desmopressin and enuresis. Possible reasons for suboptimal treatment response are explored and strategies to improve outcomes in patients for whom desmopressin is an appropriate therapy are presented. Through optimization of the treatment plan in primary and specialist care centres, the hope is that fewer patients with this distressing and often embarrassing condition will experience unnecessary delays in receiving appropriate care and achieving improvements.

Comment on: Pharmacokinetics of Tramadol and O-Desmethyltramadol Enantiomers Following Administration of Extended-Release Tablets to Elderly and Young Subjects
Allegaert K
Letter to the Editor in Drugs & Aging, February 2016, 33(2):159-160

Possible effects of repeated exposure to ibuprofen and acetaminophen on the intestinal immune response in young infants.
Langhendries JP, Allegaert K, Van Den Anker JN, Veyckemans F, Smets F
Medical Hypotheses, 2016 Feb;87:90-6
There has been an exponential increase in the frequency of immune deviations in young children. Consequently, research investigating environmental causes for this increase has become a Public Health priority. We have summarized the experimental observations and epidemiological data that could link repeated acetaminophen and ibuprofen exposure in early infancy to this increase. Recent observations on the maturational immunity of the intestinal sub-mucosal lamina propria underscore indeed the importance of prostaglandins (PGE2s). PGE2 appearing at this sub-mucosal level is a product of arachidonic acid metabolism mediated by type-2 cyclooxygenase (COX-2) situated on the membrane of many immune cells. Moreover, it seems that acetaminophen – like ibuprofen – also carries a non-selective inhibitory action on peripheral COXs, besides its central action. This inhibitory action of acetaminophen on COX2 only relates to physiological, low arachidonic acid concentrations. This explains the difference in anti-inflammatory effects. The impact of repeated inhibition of mucosal PGE2 synthesis due to COX-inhibitor exposure on maturational immunity has been demonstrated in animal experiments. Repeatedly exposed young animals do not develop tolerance to food antigens and exhibit autoimmune deviations. Several recent epidemiological studies have also reported on the magnitude of acetaminophen and ibuprofen exposure in children and the increase in immune deviations, it is important to better understand the potential negative impact of repeated inhibitions of prostaglandin synthesis by COX2s during infancy. Since acetaminophen and ibuprofen are commonly administered analgesics and antipyretics, a well-designed prospective strategy for pharmacovigilance and -epidemiology of COX-inhibitor exposure in infancy is urgently needed.

Towards rational dosing algorithms for vancomycin in neonates and infants based on population pharmacokinetic modeling
Janssen EJH, Välitalo PAJ, Allegaert K, de Cock RFW, Simons SHP, Sherwin CMT, Mouton JW, van den Anker JN, Knibbe CAJ
Antimicrobial Agents and Chemotherapy, February 2016, 60(2)
Introduction: Because of the recent awareness that vancomycin doses should aim to meet target Area Under the Curve (AUC) instead of trough concentrations, more aggressive dosing regimens are warranted, also in the pediatric population. In this study, both a neonatal and pediatric pharmacokinetic model for vancomycin were externally evaluated, and subsequently used to derive model-based dosing algorithms for neonates, infants and children.
Methods: For the external validation, predictions from previously published pharmacokinetic models were compared to new data. Simulations were performed in order to evaluate current dosing regimens and to propose a model-based dosing algorithm. AUC24h/MIC was evaluated for all investigated dosing schedules (target >400), without any concentration exceeding 40 mg/L.
Results: Both the neonatal and pediatric model of vancomycin performed well in the external datasets resulting in concentrations that were predicted correctly and without bias. For neonates, a dosing algorithm based on birth bodyweight and postnatal age is proposed with daily doses divided over 3-4 doses. For infants aged 1 year, an initial loading dose is proposed.
Conclusion: Based on the externally validated neonatal and pediatric vancomycin models, novel dosing algorithms are proposed for neonates and children aged

Neonates and medicines: a roadmap to further improve neonatal pharmaceutical care
van den Anker JN, Allegaert K
Pediatric Critical Care Medicine, February 2016, 17(2):182–183

Creatinine Assays in Early Infancy: How to Aim for a Moving Target
Allegaert K
Book chapter in Biomarkers in Kidney Disease, February 2016, pp 1-30
Glomerular filtration rate (GFR) in neonates is very low and can only be maintained due to a delicate balance between both vasodilatory effects at the afferent and vasoconstrictor effects at the efferent glomerular arteriole. Despite this low clearance capacity, interindividual variability is already extensive and can be predicted by covariates (gestational age, birth weight, postnatal age, drugs, growth restriction, or peripartal asphyxia).
We still commonly used creatinine as a proxy for renal clearance capacity. However, before creatinine values can be used to estimate renal elimination capacity, there are some issues that need to be considered related to physiology and methodology. Creatinine at birth does not yet reflect neonatal but maternal creatinine clearance, and because of passive tubular back leak instead of active secretion, creatinine clearance does not yet fully reflect GFR. Trends will be described. Moreover, absolute creatinine values also depend on the technique. The move toward harmonization through isotope dilution mass spectrometry (IDMS) traceability has helped but has not completely solved this problem. In line with recent observations in adults, more research is needed to document the potential add on the benefit of advanced biomarkers (e.g., cystatin C). In the meanwhile, IDMS-traceable creatinine observations, compared to age-dependent, assay-specific reference values, should be used to support clinical decisions.

Circadian Rhythm of Glomerular Filtration and Solute Handling Related to Nocturnal Enuresis.
Dossche L, Raes A, Hoebeke P, De Bruyne P, Vande Walle J
J Urol. 2016 Jan;195(1):162-7
Although nocturnal polyuria in patients with monosymptomatic enuresis can largely be explained by the decreased nocturnal vasopressin secretion hypothesis, other circadian rhythms in the kidney also seem to have a role. We recently documented an absent day/night rhythm in a subgroup of desmopressin refractory cases. We explore the importance of abnormal circadian rhythm of glomerular filtration and tubular (sodium, potassium) parameters in patients with monosymptomatic enuresis.
In this retrospective study of a tertiary enuresis population we collected data subsequent to a standardized screening (International Children’s Continence Society questionnaire), 14-day diary for nocturnal enuresis and diuresis, and 24-hour concentration profile. The study population consisted of 139 children with nocturnal enuresis who were 5 years or older. Children with nonmonosymptomatic nocturnal enuresis were used as controls.
There was a maintained circadian rhythm of glomerular filtration, sodium, osmotic excretion and diuresis rate in children with monosymptomatic and nonmonosymptomatic nocturnal enuresis, and there was no difference between the 2 groups. Secondary analysis revealed that in patients with nocturnal polyuria (with monosymptomatic or nonmonosymptomatic nocturnal enuresis) circadian rhythm of glomerular filtration, sodium and osmotic excretion, and diuresis rate was diminished in contrast to those without nocturnal polyuria (p <0.001).
Circadian rhythm of the kidney does not differ between patients with nonmonosymptomatic and monosymptomatic enuresis. However, the subgroup with enuresis and nocturnal polyuria has a diminished circadian rhythm of nocturnal diuresis, sodium excretion and glomerular filtration in contrast to children without nocturnal polyuria. This observation cannot be explained by the vasopressin theory alone.

Neonates and medicines: a roadmap to further improve neonatal pharmaceutical care
Allegaert K, Sherwin C
European Journal of Pediatrics, January 2016, 175(6):743-746

Prospective Evaluation of a Model-Based Dosing Regimen for Amikacin in Preterm and Term Neonates in Clinical Practice.
Smits A, De Cock RF, Allegaert K, Vanhaesebrouck S, Danhof M, Knibbe CA.
Antimicrob Agents Chemother. 2015 Oct;59(10):6344-51
Based on a previously derived population pharmacokinetic model, a novel neonatal amikacin dosing regimen was developed. The aim of the current study was to prospectively evaluate this dosing regimen. First, early (before and after second dose) therapeutic drug monitoring (TDM) observations were evaluated for achieving target trough (24 mg/liter) levels. Second, all observed TDM concentrations were compared with model-predicted concentrations, whereby the results of a normalized prediction distribution error (NPDE) were considered. Subsequently, Monte Carlo simulations were performed. Finally, remaining causes limiting amikacin predictability (i.e., prescription errors and disease characteristics of outliers) were explored. In 579 neonates (median birth body weight, 2,285 [range, 420 to 4,850] g; postnatal age 2 days [range, 1 to 30 days]; gestational age, 34 weeks [range, 24 to 41 weeks]), 90.5% of the observed early peak levels reached 24 mg/liter, and 60.2% of the trough levels were 24 mg/liter were reached at steady state in almost all patients. Trough values of 2,000 g. Prospective evaluation of a model-based neonatal amikacin dosing regimen resulted in optimized peak and trough concentrations in almost all patients. Slightly adapted dosing for patient subgroups with suboptimal trough levels was proposed. This model-based approach improves neonatal dosing individualization.

Neonatal drug therapy: The first frontier of therapeutics for children.
Allegaert K, van den Anker J
Clin Pharmacol Therapy, 2015 Sep;98(3):288-97
Knowledge about the safe and effective use of medicines in neonates has increased substantially but has resulted in few label changes. Drugs developed for use in adults are reshaped and tailored to specific neonatal indications. However, the use of drugs in neonates should not only mirror adult pharmacotherapy, but should be driven by their own specific needs. Therefore, building collaborative networks may assist to develop a newborn-driven research agenda addressing their clinical needs and diseases.

Design and feasibility of “PREMATurity as predictor of children’s Cardiovascular-renal Health” (PREMATCH): A pilot study.
Raaijmakers A, Petit T, Gu Y, Zhang Z, Wei F, Cools B, Jacobs L, Thijs L, Thewissen L, Levtchenko E, Staessen JA, Allegaert K.
Blood Pressure, 2015, 24(5):275-83
The microvasculature and macrovasculature undergo extensive, organ-specific perinatal maturation. Multiple studies show associations between low birth weight and subsequent cardiovascular dysfunction in adulthood, suggesting that extreme preterm birth interferes with this maturation process. Therefore, we designed PREMATCH (PREMATurity as predictor of Cardiovascular-renal Health) to phenotype the microcirculation and macrocirculation during childhood in former preterm infants. A well-characterized cohort of former extreme preterm birth survivors and gender- and age-matched controls (aged 8-13 years) will be investigated for microvascular and macrovascular structure and function. In addition to cognitive performance and anthropometrics, we will investigate (i) the microvascular structure and function by endothelial function (photoplethysmography), sublingual capillary glycocalyx function (sidestream dark field imaging) and retinal structure (diameters of arterioles and venules); and (ii) the macrovascular phenotype by cardiac and renal ultrasound, repeated blood pressure measurements and arterial pulse-wave recordings. The PREMATCH study is unique in its design, and ongoing recruitment demonstrates excellent feasibility. The expectation is that the results of this study will identify risk factors during childhood for subsequent cardiovascular-renal disease in the adult life of former preterm infants, while further analysis on mediators in neonatal life of this cardiovascular-renal outcome may provide new information on perinatal risk factors.

Management of hypertension in children and adolescents
De Bruyne P, Vande Walle J
International Journal of Clinical and Laboratory Medicine, 2015, 70(2):87-94
Hypertension has been recognized as an important health issue in the pediatric population over the past years. This emphasizes the need for an organized and effective plan for diagnosis and management. This review provides information to guide physicians through a structured approach to (1) screen children for hypertension during routine visits; (2) use normative blood pressure tables for diagnosis and classification; (3) perform a clinical evaluation to identify the presence of risk factors, comorbidities and/or target organ damage; and (4) initiate an individualized plan of care that includes follow-up blood pressure measurement, therapeutic lifestyle changes and – if necessary – pharmacological therapies.

Augmented renal clearance implies a need for increased amoxicillin-clavulanic acid dosing in critically ill children
De Cock PA, Standing JF, Barker CI, de Jaeger A, Dhont E, Carlier M, Verstraete AG, Delanghe JR, Robays H, De Paepe P.
Antimicrobial Agents and Chemotherapy, November 2015, 59(11):7027-35
Few data are available to guide amoxicillin/clavulanic acid dosing in critically ill children. The primary objective of this study was to investigate the pharmacokinetics of both compounds in this pediatric subpopulation. Patients admitted to the pediatric ICU in whom intravenous amoxicillin/clavulanic acid was indicated (25-35 mg/kg every 6h) were enrolled. Population pharmacokinetic analysis was conducted and clinical outcome was documented. 325 amoxicillin and 151 clavulanic acid blood samples were collected from 50 patients (median age: 2.58 years; range: 1 month-15 years). A three-compartment model for amoxicillin and a two-compartment model for clavulanic acid best described the data, in which allometric weight scaling and maturation functions were added a priori to scale for size and age. In addition, plasma Cystatin C and concomitant treatment with vasopressors were identified to have a significant influence on amoxicillin clearance. The typical population values of clearance for amoxicillin and clavulanic acid were 17.97 L/h/70kg and 12.20 L/h/70kg, respectively. In 32% of treatments, amoxicillin/clavulanic acid therapy was stopped prematurely due to clinical failure and the patient was switched to broader spectrum antibiotic treatment. Monte Carlo simulations demonstrated that four hourly dosing of 25 mg/kg was required to achieve the therapeutic target for both amoxicillin and clavulanic acid. For patients with augmented renal function, a 1 hour infusion was preferable to bolus dosing. Current published dosing regimens result in subtherapeutic concentrations in the early period of sepsis due to augmented renal clearance, which risks clinical failure in critically ill children, and therefore need to be updated.

Physiologically Based Pharmacokinetic Predictions of Tramadol Exposure Throughout Pediatric Life: an Analysis of the Different Clearance Contributors with Emphasis on CYP2D6 Maturation.
T’jollyn H, Snoeys J, Vermeulen A, Michelet R, Cuyckens F, Mannens G, Van Peer A, Annaert P, Allegaert K, Van Bocxlaer J, Boussery K.
AAPS Journal, November 2015, 17(6):1376-87
This paper focuses on the retrospective evaluation of physiologically based pharmacokinetic (PBPK) techniques used to mechanistically predict clearance throughout pediatric life. An intravenous tramadol retrograde PBPK model was set up in Simcyp® using adult clearance values, qualified for CYP2D6, CYP3A4, CYP2B6, and renal contributions. Subsequently, the model was evaluated for mechanistic prediction of total, CYP2D6-related, and renal clearance predictions in very early life. In two in vitro pediatric human liver microsomal (HLM) batches (1 and 3 months), O-desmethyltramadol and N-desmethyltramadol formation rates were compared with CYP2D6 and CYP3A4 activity, respectively. O-desmethyltramadol formation was mediated only by CYP2D6, while N-desmethyltramadol was mediated in part by CYP3A4. Additionally, the clearance maturation of the PBPK model predictions was compared to two in vivo maturation models (Hill and exponential) based on plasma concentration data, and to clearance estimations from a WinNonlin® fit of plasma concentration and urinary excretion data. Maturation of renal and CYP2D6 clearance is captured well in the PBPK model predictions, but total tramadol clearance is underpredicted. The most pronounced underprediction of total and CYP2D6-mediated clearance was observed in the age range of 2-13 years. In conclusion, the PBPK technique showed to be a powerful mechanistic tool capable of predicting maturation of CYP2D6 and renal tramadol clearance in early infancy, although some underprediction occurs between 2 and 13 years for total and CYP2D6-mediated tramadol clearance.

Neonatal medicines research: challenges and opportunities
Samardzic J, Turner MA, Ralph Bax R, Allegaert K
Expert Opin. Drug Metab. Toxicol. July 2015, 11(7):1041-52
Introduction: The key feature of the newborn is its fast age-dependent maturation, resulting in extensive variability in pharmacokinetics and -dynamics, further aggravated by newly emerging covariates like treatment modalities, environmental issues or pharmacogenetics. This makes clinical research in neonates relevant and needed, but also challenging. Areas covered: To improve this knowledge, tailoring research tools as well as building research networks and clinical research skills for neonates are urgently needed. Tailoring of research tools is illustrated using the development of dried blood spot techniques and the introduction of micro-dosing and -tracer methodology in neonatal drug studies. Both techniques can be combined with sparse sampling techniques through population modeling. Building research networks and clinical research skills is illustrated by the initiatives of agencies to build and integrate knowledge on neonatal pharmacotherapy
through dedicated working groups. Expert opinion: Challenges relating to neonatal medicine research can largely be overcome. Tailored tools and legal initiatives, combined with clever trial design will result in more robust information on neonatal pharmacotherapy. This necessitates collaborative efforts between clinical researchers, sponsors, regulatory authorities, and last but not least patient representatives and society.

Simplified screening criteria for HNF1B analysis.
Anke A Raaijmakers, Djalila Mekahli and Elena N Levtchenko
Kidney International (Letter to the Editor), June 2015, 87(6):1258-9
To the Editor: Indications for HNF1B analysis in subjects with congenital anomalies of kidneys and urinary tract (CAKUT) remain controversial and a frequently discussed subject. The large phenotypic variability and the high rate of de novo mutations partly explain this discussion.
Recently, Faguer et al.1 have addressed this challenging issue by developing an exhaustive scoring system. This 17-item score contains clinical, biochemical, familial, and pathological findings in affected subjects. Although the authors claim that their score performed with a sensitivity of 98.2% and a NPV of 99%, we have some connotations to address.
We recently applied the score of Faguer et al.1 in a cohort of children and adults identified with HNF1B mutations in a prospective cohort of patients with CAKUT2 and found that three patients would have been missed, as especially in children an exhaustive list of symptoms is not always (yet) present.
In contrast, applying the simplified screening criteria excluding patients with unilateral abnormalities in the absence of major criteria (fetal hyperechogenic kidneys, multicystic dysplastic kidney, renal agenesis, hypoplastic or dysplastic kidneys, or cysts from unknown origin)2 would improve the detection rate from 10 to 19% and a 50% reduction in patients to be screened, in line with the improvement by the score of Faguer et al.1
In our opinion, an easy screening protocol proposed in our study is suitable for daily clinical practice, although we realize that both protocols should be applied to larger databases to substantiate their use and to validate their performance.

Design and feasibility of “PREMATurity as predictor of children’s Cardiovascular-renal Health” (PREMATCH): A pilot study.
Raaijmakers A, Petit T, Gu Y, Zhang Z, Wei F, Cools B, Jacobs L, Thijs L, Thewissen L, Levtchenko E, Staessen JA, Allegaert K.
Blood Pressure, June 2015, 24:1-9
The microvasculature and macrovasculature undergo extensive, organ-specific perinatal maturation. Multiple studies show associations between low birth weight and subsequent cardiovascular dysfunction in adulthood, suggesting that extreme preterm birth interferes with this maturation process. Therefore, we designed PREMATCH (PREMATurity as predictor of Cardiovascular-renal Health) to phenotype the microcirculation and macrocirculation during childhood in former preterm infants. A well-characterized cohort of former extreme preterm birth survivors and gender- and age-matched controls (aged 8-13 years) will be investigated for microvascular and macrovascular structure and function. In addition to cognitive performance and anthropometrics, we will investigate (i) the microvascular structure and function by endothelial function (photoplethysmography), sublingual capillary glycocalyx function (sidestream dark field imaging) and retinal structure (diameters of arterioles and venules); and (ii) the macrovascular phenotype by cardiac and renal ultrasound, repeated blood pressure measurements and arterial pulse-wave recordings. The PREMATCH study is unique in its design, and ongoing recruitment demonstrates excellent feasibility. The expectation is that the results of this study will identify risk factors during childhood for subsequent cardiovascular-renal disease in the adult life of former preterm infants, while further analysis on mediators in neonatal life of this cardiovascular-renal outcome may provide new information on perinatal risk factors.

Criteria for HNF1B analysis in patients with congenital abnormalities of kidney and urinary tract.
Raaijmakers A, Corveleyn A, Devriendt K, van Tienoven TP, Allegaert K, Van Dyck M, van den Heuvel L, Kuypers D, Claes K, Mekahli D, Levtchenko E.
Nephrology, Dialysis, Transplantation, May 2015,30(5):835-42
Congenital anomalies of kidneys and urinary tract (CAKUT) are the most predominant developmental disorders comprising ∼20-30% of all anomalies identified in the prenatal period. Mutations in hepatocyte nuclear factor 1-beta (HNF-1β) involved in the development of kidneys, liver, pancreas and urogenital tract are currently the most frequent monogenetic cause of CAKUT found in 10-30% of patients depending on screening policy and study design. We aimed to validate criteria for analysis of HNF1B in a prospective cohort of paediatric and adult CAKUT patients.
We included CAKUT patients diagnosed in our paediatric and adult nephrology departments from January 2010 until April 2013 based on predefined screening criteria. Subjects presenting with at least one major renal criterion or one minor renal criterion combined with one or more extra-renal criteria in the personal history or a familial history of renal or extra-renal manifestations were considered eligible.
We prospectively screened 205 patients and detected HNF1B mutations in 10% [n = 20, 12 children, median age 4.2 (range 0-13.1) years and 8 adults, median age 34.8 (range 16.6-62) years]. We observed that bilateral renal anomaly, renal cysts from unknown origin, a combination of two major renal anomalies and hypomagnesaemia were predictive for finding HNF1B mutations (P < 0.001; P < 0.001; P = 0.004; P = 0.008, respectively).
We demonstrated that HNF1B mutations are responsible for ∼10% of CAKUT cases, both in children and in adults. Based on our results we propose adapted criteria for HNF1B analysis to reduce the screening costs without missing affected patients. These criteria should be reaffirmed in a larger validation cohort.

Neonatal creatinemia trends as biomarker of subsequent cognitive outcome in extremely low birth weight neonates
Anke Raaijmakers, Els Ortibus, Theun P. van Tienoven , Christine Vanhole, Elena Levtchenk, Karel Allegaert
Early Human development, 2015, 91:367-372
Background and aims: Serum creatinine is traditionally used as a marker of renal function in neonates and relates to gestational age and disease severity in extremely low birth weight (ELBW) infants. Creatinine is commonly used as a biomarker for early morbidity, but we aim to compare postnatal creatinemia trends as a biomarker for subsequent cognitive outcome. We hypothesize that impaired microcirculation not only in the kidney, but also in general (i.e. brain development) can explain this possible link. Study design and outcomemeasures: A cohort of ELBWinfants was analyzed byBayley Scales of Infant Development (BSID-II) at the corrected age of 2 years old. Besides other perinatal indicators, neonatal creatinemia trends of survivors (n = 140) and BSID scores (n = 96) are compared and analyzed using optimal matching analysis. Hierarchical clustering analysis is applied to identify createnimia trends.
Results: Four different creatinemia trends were identified (persistently high, normal, low, high but normalizing). A low creatinemia trend is significantly associated with the lowest percentages of postnatal corticosteroids, NSAIDS and intraventricular hemorrhage (p = 0.005, p = 0.013 and p = 0.041 respectively) compared to a normal or persistently high creatinemia trend and associated with the best cognitive outcome (+13 points compared to the mean creatinemia trend and +23 points compared to a persistently high creatinemia trend).
Conclusions: Creatinemia trends after birth are not only useful to predict renal function, but are also associated with cognitive outcome in extremely low birth weight infants. Neonates who have low creatinemia trends after birth, have the highest BSID scores at the age of two years old.

Drug-Induced Renal Damage in Preterm Neonates: State of the Art and Methods for Early Detection
Anna Girardi, Emanuel Raschi, Silvia Galletti, Elisabetta Poluzzi, Giacomo Faldella, Karel Allegaert, Fabrizio De Ponti
Drug Safety April 12, 2015
Abstract Only a small fraction of drugs widely used in neonatal intensive care units (NICU) are specifically authorized for this population. Even if unlicensed or off-label use is necessary, it is associated with increased adverse drug reactions, which must be carefully weighed against expected benefits. In particular, renal damage is frequent among preterm babies, and is considered a predisposing factor for the development of chronic kidney disease in adulthood. Apart from specific conditions affecting premature neonates (e.g. respiratory distress syndrome, perinatal asphyxia), drugs play an important role in impairing renal function because of well-known nephrotoxicity and/ or interaction with renal developmental factors. From a review of the available studies on drug use in NICU patients, we identified and described the most commonly administered drugs that are correlated to renal damage. Early detection of kidney injury is becoming an essential aspects for clinicians because of the limited number of biomarkers applicable in the neonatal population. Postnatal changes of biochemical processes that influence pharmacokinetic and pharmacodynamic aspects need to be further investigated in order to better understand the mechanisms of drug toxicity in this population. The most promising strategies for dose adjustment and therapeutic schemes are discussed. The purpose of this review was to describe current knowledge on drug use among premature babies and their implication in kidney injury development, as well as to highlight available strategies for early detection of renal damage.

Novel model-based dosing guidelines for gentamicin and tobramycin in preterm and term neonates
Pyry A. J. Valitalo, John N. van den Anker, Karel Allegaert, Roosmarijn F. W. de Cock, Matthijs de Hoog, Sinno H. P. Simons, Johan W. Mouton and Catherijne A. J. Knibbe
J Antimicrob Chemother March 2015
Objectives: In the heterogeneous group of preterm and term neonates, gentamicin and tobramycin are mainly dosed according to empirical guidelines, after which therapeutic drug monitoring and subsequent dose adaptation are applied. In view of the variety of neonatal guidelines available, the purpose of this study was to evaluate target concentration attainment of these guidelines, and to propose a new model-based dosing guideline for these drugs in neonates.
Methods: Demographic characteristics of 1854 neonates (birth weight 390–5200 g, post-natal age 0–27 days) were extracted from earlier studies and sampled to obtain a test dataset of 5000 virtual patients. Monte Carlo simulations on the basis of validated models were undertaken to evaluate the attainment of target peak (5–12 mg/L) and trough (,0.5 mg/L) concentrations, and cumulative AUC, with the existing and proposed guidelines.
Results: Across the entire neonatal age and weight range, the Dutch National Formulary for Children, the British National Formulary for Children and Neofax resulted in adequate peak but elevated trough concentrations (63%–90% above target). The Red Book resulted in adequate trough but inadequate peak concentrations (66%–74% below target). The proposed dosing guideline (4.5 mg/kg gentamicin or 5.5 mg/kg tobramycin) with a dosing interval based on birth weight and post-natal age leads to adequate peak concentrations with only 33%–38% of the trough concentrations above target, and a constant AUC across weight and post-natal age.
Conclusions: The proposed neonatal dosing guideline for gentamicin and tobramycin results in improved attainment of target concentrations and should be prospectively evaluated in clinical studies to evaluate the efficacy and safety of this treatment.

Physiology-Based IVIVE Predictions of Tramadol from in Vitro Metabolism Data
Huybrecht T’jollyn, Jan Snoeys, Pieter Colin, Jan Van Bocxlaer, Pieter Annaert, Filip Cuyckens, An Vermeulen, Achiel Van Peer, Karel Allegaert, Geert Mannens and Koen Boussery
Pharmaceutical Research, January 2015, 32, 260–274
Purpose: To predict the tramadol in vivo pharmacokinetics in adults by using in vitro metabolism data and an in vitro-in vivo extrapolation (IVIVE)-linked physiologically-based pharmacokinetic (PBPK) modeling and simulation approach (Simcyp®).
Methods: Tramadol metabolism data was gathered using metabolite formation in human livermicrosomes (HLM) and recombinant enzyme systems (rCYP). Hepatic intrinsic clearance (CLintH) was (i) estimated from HLM corrected for specific CYP450 contributions from a chemical inhibition assay (model 1); (ii) obtained in rCYP and
corrected for specific CYP450 contributions by study-specific intersystem extrapolation factor (ISEF) values (model 2); and (iii) scaled back from in vivo observed clearance values (model 3). The modelpredicted clearances of these three models were evaluated against observed clearance values in terms of relative difference of their geometric means, the fold difference of their coefficients of variation, and relative CYP2D6 contribution.
Results: Model 1 underpredicted, while model 2 overpredicted the total tramadol clearance by −27 and +22%, respectively. The CYP2D6 contribution was underestimated in both models 1 and 2. Also, the variability on the clearance of those models was slightly underpredicted. Additionally, blood-to-plasma ratio and
hepatic uptake factor were identified as most influential factors in the prediction of the hepatic clearance using a sensitivity analysis.
Conclusion: IVIVE-PBPK proved to be a useful tool in combining tramadol’s low turnover in vitro metabolism data with systemspecific physiological information to come up with reliable PK predictions in adults.

Clinical Pharmacology in Neonates: Small Size, Huge Variability
Karel Allegaert, John N. van den Anker
Neonatology 2014;105:344–349
Drug therapy is a powerful tool for improving neonatal outcome. Despite this, neonatologists still routinely prescribe off-label compounds developed for adults and extrapolate doses from those used for children or adults. Knowledge integration through pharmacokinetic modeling is a method that could improve the current situation. Such predictive models may convert neonatal pharmacotherapy from explorative to confirmatory. This can be illustrated by research projects related to the prediction of neonatal renal clearance and neonatal glucuronidation. This type of model will also improve the current knowledge of neonatal (patho)physiology. In the meanwhile, the fields of clinical pharmacology (e.g. pharmacokinetic/pharmacodynamic modeling and pharmacogenetics) and neonatology (e.g. whole-body cooling and the lower limit of viability) have both matured, resulting in new research topics. However, in order for the modeling and the newly emerging topics to become effective tools, they need to be tailored to the specific characteristics of neonates. Consequently, the field of neonatal pharmacotherapy needs dedicated neonatologists who continue to raise the awareness that off-label practices, eminencebased dosing regimens and the absence of neonatal drug formulations all reflect suboptimal care.

Paired measurement of urinary creatinine in neonates based on a Jaffe and an enzymatic IDMS-traceable assay
Karel Allegaert, Pieter Vermeersch, Anne Smits, Djalila Mekahli, Elena Levtchenko and Steven Pauwels
BMC Nephrology 2014, 15:62
Urinary creatinine can be quantified by Jaffe or enzymatic assays and is commonly used as denominator of urinary excretion of electrolytes or protein. Paired analysis in pediatric and adult samples documented inter-assay differences (up to 80%). We verified the interchangeability of two IDMS-traceable assays (Jaffe and enzymatic) for neonatal urine and report on neonatal urinary creatinine values using these IDMS-traceable methods.
Creatinine was measured in 84 neonatal urine samples from 46 neonates by an IDMS traceable Jaffe and enzymatic assay (Roche Diagnostics, Cobas c702 module). Creatinine values, differences in urinary creatinine and clinical characteristics were described and covariates of between assay difference were explored (Wilcoxon, Bland-Altman, correlation, multiple regression).
Median Jaffe and enzymatic urinary creatinine concentrations were 9.25 (range 3.7-42.2) and 9.15 (range 3.8-42.9) mg/dL respectively, resulting in a median difference of 0.08 (SD 0.6, range −2.4 to 0.96) mg/dL. In a multiple regression model, urinary enzymatic creatinine concentration (r = 0.45) and postnatal age (r = −0.59) remained independent variables of the difference between both assays (r2 adj = 0.45).
The tested IDMS-traceable assays showed interchangeable in heterogeneous neonatal urine samples. Using these assays, neonatal urinary creatinine showed 5–20 fold lower values than those observed in children or adults with a significant negative correlation with postnatal age.

Cystatin C in newborns: a promising renal biomarker in search for standardization and validation
Karel Allegaert, Djalila Mekahli, and John van den Anker
The Journal of Maternal-fetal & neonatal Medicine, November 5, 2014
Objective: Neonatologists still commonly use creatinine as a proxy for renal clearance, despite issues related to neonatal (patho)physiology and methodology (assay variability). Cystatin C (CysC) has been suggested to be a more reliable biomarker, but assay related differences have also been reported in children and adults. We are unaware of any review on the assay related impact on CysC reference values in newborns.
Methods: A structured literature search was performed on published CysC values in (pre)term neonates.
Results: The extensive range (>5-fold) in serum CysC observations in neonates in part relates to the fact that CysC concentrations are higher at birth with subsequent decrease and that CysC concentrations are higher in preterm compared to term neonates. The CysC assay matters while disease characteristics also affect CysC values, but not always in the predicted direction.
Conclusions: Similar to creatinine, the extensive CysC range in neonates is only in part explained by renal (patho)physiology. Its applicability in neonatal medicine can be further improved by use of assay specific reference values, adapted to neonatal renal physiology (e.g. weight, age) and should be compared to a gold standard such as inulin clearance.

Tailored tools to improve pharmacotherapy in infants
Karel Allegaert
Expert Opinion on Drug Metabolism & toxicology, Vol 10 No 8 Aug 2014
Introduction: Extensive within-population variability is the essence of neonatal pharmacology. Despite this, infants remain one of the last therapeutic orphans. Together with additional legal initiatives, tailoring of already available tools (modeling, covariates, pharmacovigilance) may significantly improve pharmacotherapy in infants.
Areas covered: Modeling approaches that hold the promise to improve pharmacotherapy in infants are between-compound extrapolation for compounds that undergo the same route of elimination and integration of time-varying physiology to adapt for the fast maturational changes. Besides these maturational covariates (size, age), newly emerging covariates relate to novel treatment modalities (extracorporeal circulation, hypothermia), environmental issues (microbiome, critical illness) or pharmacogenetics. All these covariates interact with the maturational variation. Finally, pharmacovigilance also needs to be tailored to the characteristics of this population. This relates to preventive strategies, signal detection and assessment of causality. Expert opinion: Knowledge on pharmacotherapy in infants is lagging. Tailoring available tools to the specific characteristics (maturation) and clinical needs (newly emerging covariates) of infants is feasible but needs creativity and a multidisciplinary collaboration between modelers, academia, clinical researchers and, obviously, the public, including parents.

Pharmacokinetic model development and validation to improve pharmacotherapy in neonates
Karel Allegaert
Proc Belg Roy Acad Med Vol 3:146-156 2014
Drug therapy is important to improve the outcome of neonates. Despite this, paediatricians commonly still prescribe drugs primarily developed for use in adults. Solely based on existing knowledge concerning the pathophysiology in adults, they extrapolate the dosing regimens from adults for use in children of all age. A powerful tool to improve neonatal pharmacotherapy and facilitate clinical studies is knowledge integration through pharmacokinetic (PK) modelling. PK modelling is through mechanism based PK or physiology-based (PB) PK. Mechanism based models apply a bottom-up ‘from compound to model’ concept: based on drug specific observations, covariates are described, resulting in mechanism-based models. PB-PK applies a top-down ‘from physiology to clinical observations’ concept: based on available data on neonatal physiology (e.g. weight, cardiac output, renal function), a PB-PK model is developed.
Such models can guide study design and convert neonatal pharmacotherapy from explorative to confirmatory. The consecutive steps taken to model neonatal renal drug clearance illustrate the feasibility of such an approach. Besides clinical relevance, the same observations also unveil maturational patterns, and guide research addressing gaps in the knowledge of developmental physiology. This will be illustrated using as examples cefazolin (maturation of renal tubular transport) and propylene glycol (hepatic compared to renal elimination) clearance.

Enzymatic isotope dilution mass spectrometry (IDMS) traceable serum creatinine is preferable over Jaffe in neonates and young infants
Karel Allegaert, Steven Pauwels , Anne Smits , Kaat Crèvecoeur , John van den Anker , Djalila Mekahli and Pieter Vermeersch
Clin Chem Lab Med 2014
Letter to the editor

A Neonatal Amikacin Covariate Model Can Be Used to Predict Ontogeny of Other Drugs Eliminated Through Glomerular Filtration in Neonates
Roosmarijn F. W. De Cock, Karel Allegaert, Catherine M. T. Sherwin, Elisabet I. Nielsen, Matthijs de Hoog, Johannes N. van den Anker, Meindert Danhof, Catherijne A. J. Knibbe
Pharmaceutical Research, March 2014, Vol 31,3,754-767
Purpose Recently, a covariate model characterizing developmental changes in clearance of amikacin in neonates has been developed using birth bodyweight and postnatal age. The aim of this
study was to evaluate whether this covariate model can be used to predict maturation in clearance of other renally excreted drugs.
Methods Five different neonatal datasets were available on netilmicin, vancomycin, tobramycin and gentamicin. The extensively validated covariate model for amikacin clearance was used to predict
clearance of these drugs. In addition, independent reference models were developed based on a systematic covariate analysis.
Results The descriptive and predictive properties of the models developed using the amikacin covariate model were good, and fairly similar to the independent reference models (goodness-of-fit plots, NPDE). Moreover, similar clearance values were obtained for both approaches. Finally, the same covariates as in the covariate model of amikacin, i.e. birth bodyweight and postnatal age, were identified on clearance in the independent reference models.
Conclusions This study shows that pediatric covariate models may contain physiological information since information derived from one drug can be used to describe other drugs. This semiphysiological approach may be used to optimize sparse data analysis and to derive individualized dosing algorithms for drugs in children.

Simultaneous Pharmacokinetic Modeling of Gentamicin, Tobramycin and Vancomycin Clearance from Neonates to Adults: Towards a Semi-physiological Function for Maturation in Glomerular Filtration
Roosmarijn F. W. De Cock, Karel Allegaert, Janneke M. Brussee, Catherine M. T. Sherwin, Hussain Mulla, Matthijs de Hoog, Johannes N. van den Anke, Meindert Danhof, Catherijne A. J. Knibbe
Pharmaceutical research, Okt 2014, Volume 31,10, pp2643-2654
Purpose Since glomerular filtration rate (GFR) is responsible for the elimination of a large number of water-soluble drugs, the aim of this study was to develop a semi-physiological function for GFR maturation from neonates to adults.
Methods In the pharmacokinetic analysis (NONMEM VI) based on data of gentamicin, tobramycin and vancomycin collected in 1,760 patients (age 1 day–18 years, bodyweight 415 g–85 kg), a distinction was made between drug-specific and system-specific information. Since the maturational model for clearance is considered to contain system-specific information on the developmental changes in GFR, one GFR maturational function was derived for all three drugs.
Results Simultaneous analysis of these three drugs showed that maturation of GFR mediated clearance from preterm neonates to adults was best described by a bodyweight-dependent exponent (BDE) function with an exponent varying from 1.4 in neonates to 1.0 in adults (ClGFR=Cldrug*(BW/4 kg)BDE with BDE= 2.23*BW−0.065). Population clearance values (Cldrug) for gentamicin, tobramycin and vancomycin were 0.21, 0.28 and 0.39 L/h for a full term neonate of 4 kg, respectively.
Discussion Based on an integrated analysis of gentamicin, tobramycin and vancomycin, a semi-physiological function for GFR mediated clearance was derived that can potentially be used to establish evidence based dosing regimens of renally excreted drugs in children.

Project reports

We are working really hard on it right now


We are working really hard on it right now

Presentations on symposia and meetings

Sharing Progress in Neonatology (SPIN) including 31th International Workshop on Surfactant Replacement
Location: Naples, Italy
Date:03/06/2016 – 04/06/2016

Adverse drug reactionsin neonates
Karel Allegaert

Euroanaesthesia 2016
Location: Londen, UK
Date: 28/05/2016-30/05/2016

Which drugs used in paediatric anaesthesia do we need more information on?
Karel Allegaert

44th BVK-SBP congress
Location: Brussels, Belgium
Date: 10/03/2016-11/03/2016

Effect of food and pharmaceutical formulation on desmopressin pharmacokinetics in children: a case for the use of modeling and simulation in pediatric drug research
Robin Michelet, Lien Dossche, Pauline De Bruyne,Pieter Colin, Koen Boussery, Johan Vande Walle, Jan Van Bocxlaer, An Vermeulen

In pediatric drug research, pharmacokinetics and pharmacodynamics (PK/PD) are often investigated in healthy young volunteers, but this methodology hardly takes into account specific differences between adults and children. However, clinical trials in children are hard and yield less data (sparse sampling). To accommodate for this, population PK/PD analysis can be applied to extract more information out of existing data and, by means of simulation, generate new knowledge and improve future data collection. In this study, two studies regarding desmopressin (DDAVP) were analyzed to investigate how the drug product and intake of food influence DDAVP PK in children.

Bioequivalence in adults does not mean bioequivalence in children

For a new formulation of an existing drug, as well as for generics, one has only to demonstrate pharmacokinetic (PK) bioequivalence with the original formulation to obtain registration. This PK tests are performed in healthy young volunteers, taking for granted that PK follows pharmacodynamics (PD). However, this methodology hardly takes in account potential gender, size, age, maturation specific differences in bioequivalence. FDA and EMA-regulation on pediatric drug research have tried to find a compromise between minimal exposure of children to a pediatric research program, and acquiring minimal PK/PD and safety-data in children to reassure safe prescription of the drug, and therefore do not request bioequivalence studies in the pediatric age. The aim of this overview was to question if bioequivalence between different solutions is similar over all populations.

Predictive value of urinary osmolality in the early morning for desmopressin response
Dossche L, Raes A, Mauer R, De Bruyne P, Debruyn N, Cornelis AS, Vande Walle J

Desmopressin (dDAVP), a synthetic vasopressin analogue, is a level 1, grade A treatment of monosymptomatic enuresis nocturna (MNE). Although evidence based results show superiority of dDAVP above placebo, only 30 % of patients reach complete continence. Surrogate parameters predicting the dDAVP response would be useful in individualizing therapy in children with nocturnal enuresis. They have been an issue for debate and research in the past decades. Urinary osmolality in the morning was proposed by several authors, but without convincing results. The aim of this study was to explore the potential value of urinary osmolality in an early morning sample as a surrogate parameter for dDAVP response.

Therapy-resistant enuresis in adolescents, when sporting in the evening

Monosymptomatic nocturnal enuresis (MNE) is frequently related to nocturnal polyuria. Desmopressin (dDAVP), a synthetic vasopressin analogue, is a level A, grade I treatment option in these children. In the past years we observed 6 adolescents (3 cyclers + 3 footballers, 14-18 years) with MNE from sport schools, who had
dDAVP-resistant nocturnal polyuria, especially on nights following evenings with intensive physical training. This contrasted with our initial idea that following sport and dehydration, they should have lower diuresis-volumes overnight. The aim of this study was to investigate pathophysiological mechanisms that
might explain dDAVP therapy-resistance.

3rd International Neonatal Symposium
Location: Arlamow, Poland
Date: 08/10/2015-10/10/2015

Wiser use of antibiotics in nosocomial infections?
Allegaert K

Developmental pharmacokinetics reflects developmental physiology
Allegaert K

jENS congress
Location: Budapest
Date: 16/09/2015-20/09/2015

Wise(r) use of antibiotics in neonates?
Allegaert K

Vancomycin therapeutic drug monitoring in neonates: are there intra/inter-assay differences?
A Smits, M Oyaert, P Vermeersch, V Cossey, G Naulaers, S Pauwels, I Spriet, K Allegaert

Quantification of the impact of pharmacogenetics on tramadol disposition in early infancy
K Allegaert, V Cossey, C Vanhole, J de Hoon, M Matic, R van Schaik, J van den Anker, S de Wildt

Wise use of antibiotics in nosocomial infections?
K Allegaert

Maturation drives paracetamol glucuronidation in early infancy
E Krekels, S van Hal, K Allegaert, J de Hoon, A Debeer, D Tiboel, M Danhof, C Knibbe

ESPN Meeting
Location: Brussels
Date: 03/09/2015-05/09/2015

(Re)introduction of alarm therapy in children with refractory monosymptomatic nocturnal enuresis

Monosymptomatic nocturnal enuresis (MNE) is defined by the ICCS classification of 2006 as enuresis without signs of bladder dysfunction. Alarm therapy and/or desmopressin (dDAVP) are both Level I Grade A recommended therapeutic options. But little is known in refractory cases. The aim was to analyze the characteristics and outcome of patients with severe monosymptomatic enuresis (>5/7 nights), referred to a tertiary centre, when they are submitted to a (new) alarm therapy trial.

Predictive value of urinary osmolality in the early morning for desmopressin response in enuresis

Desmopressin (dDAVP), a synthetic vasopressin analogue is a level 1, grade A treatment of monosymptomatic nocturnal enuresis (MNE). Although evidence based results show superiority of dDAVP above placebo, only 30 % of patients reach complete continence. Surrogate parameters predicting the dDAVP response would be useful in individualizing therapy in children with nocturnal enuresis. They have been an issue for debate and research in the past decades. Urinary osmolality in the morning was proposed by several authors, but without convincing results.
The aim of this study was to explore the potential value of urinary osmolality in an early morning sample as a surrogate parameter for dDAVP response.
CONCLUSION: Urinary osmolality in the morning has no added value in predicting desmopressin response

Drugs and the kidneyin the neonatal period: ‘how to dose renally cleared drugs in neonates’
Allegaert K

EAVPT Meeting
Location: Nantes
Date: 19/07/2015-22/07/2015

The ontogeny of hepatic CYP3A, CYP2C and CYP2E enzyme activity in conventional pigs

The anatomy and physiology of pigs is closely related to human characteristics. Therefore, the use of pigs as an animal model to study the pharmacokinetic (PK) behavior of drugs in therapeutic subpopulations, including pediatrics, could be of interest. One of the key PK processes, biotransformation, is primarily mediated by the cytochrome P450 (CYP) enzyme system. Literature reports have demonstrated a high homology between human and porcine CYP3A, 2C and 2E in adults,
namely at least 75%, 62% and 79% amino acid sequence identity, respectively. However, data regarding the ontogeny of porcine CYP enzymes are lacking. Therefore, in order to assess whether piglets might serve as a model for pediatric PK studies, knowledge regarding the ontogeny of the CYP enzymes in pigs is mandatory.
Liver samples were collected immediately after euthanasia from 16 pigs (8 males and 8 females, Hybrid sow x Pietrain boar) of different ages (2 days, 4 and 8 weeks, 6 months-old). Samples were snap-frozen and stored at <-80°C until analysis. Microsomes were prepared by a differential centrifugation method. Midazolam, tolbutamide and chlorzoxazone probe drugs were used to determine the in vitro CYP3A, 2C and 2E catalytic activity, respectively. The corresponding metabolites, namely 1-hydroxy-midazolam, 4-hydroxy-tolbutamide and 6-hydroxychlorzoxazone, were quantified using a validated UHPLC-MS/MS method (1). Furthermore, the microsomal protein per gram of liver was determined as it is an important scaling factor in the extrapolation of the obtained in vitro enzyme activities to in vivo (2).
The biotransformation of midazolam, tolbutamide and chlorzoxazone increased with age. The mean (±SD) CYP3A activity was 60.5 (±45.7) and 83.3 (±20.7) pmol/min/mg protein at the age of 2 days, 971.1 (±367.8) and 1072.7 (±371.7) pmol/min/mg protein at the age of 4 weeks and 723.4 (±146.3) and 1134.7 (±282.6) pmol/min/mg protein at 8 weeks of age for the barrows and sows, respectively. CYP2C activity at the same ages increased from 20.1 (±12.3) and 29.1 (±18.5) to 78.3 (±25.6) and 106.7 (±69.1) and 103.5 (±39.6) and 170.2 (±71.9) pmol/min/mg protein, while the activity of CYP2E was 539.3 (±251.0) and 643.3 (±220.3), 747.7 (±134.8) and 948.9 (±246.2) and 957.9 (±221.7) and 1549.8 (±345.0) pmol/min/mg protein, respectively for the barrows and sows. Significant sex differences (P < 0.05) were only observed at 8 weeks of age. These data show similar trends with human CYP ontogeny.
This research is supported by the Agency for Innovation by Science and Technology in Flanders (IWT no. 141427) and is in line with the Safe-Pedrug consortium.

Comparison of iohexol and endogenous creatinine clearance as estimators of glomerular filtration rate in piglets at different age categories

The glomerular filtration rate (GFR) is considered to be a very important parameter of the renal function. In clinical routine, equations based on serum and urinary creatinine concentrations are still commonly used to determine the GFR despite their disadvantages. These disadvantages include confounding variables such as high protein intake and inability to detect mild kidney disease. Especially in the paediatric subpopulation, validated methods and adapted formulas to accurately determine the GFR function are lacking (Gretz et al., 2007). Over the last decade, iohexol has proven to be a sensitive and selective marker for GFR. Iohexol is a non-radiolabeled contrast medium, which is cleared solely by glomerular filtration. It has already been successfully applied in both human and veterinary medicine and seems to be of particular interest in the paediatric population as well. Since the renal function of pigs and humans display great similarities, the aim of this study was to assess the gender and age related differences in GFR in piglets based both on creatinine and iohexol clearance. These results might then have a predictive value for GFR determination in a human paediatric setting.
The GFR was measured in 16 male and 16 female piglets at 8 days, 4 and 8 weeks of age. Each animal received an intravenous injection of 64.7 mg kg-1 BW iohexol (Omnipaque 300©). Blood and urine samples were taken before and at different time-points after injection. Creatinine concentrations in plasma and urine were
obtained with an enzymatic assay. Endo- and exo-iohexol concentrations were measured by an in-house validated high-performance liquid chromatography method with ultraviolet detection (De Baere et al., 2012). The area under the plasma concentration time curve from time 0 to 24 h (AUC_0–24 h) was determined by WinNonlin 6.3. Whereafter, the clearance of endo- and exo-iohexol was calculated.
The results will be presented at the EAVPT congress.
ESDPPP Meeting
Location: Belgrade
Date: 23/06/2015-26/06/2015

Dose-finding study and phannacodynamic assessment of propofol for (semi-)elective intubation in neonates
Anne Smits, Liesbeth Thewissen, Alexander Caicedo, Johan Nicolai, Pieter Annaert, Gunnar Naulaers, Karel Allegaert

Introduction: The optimal propofol dose and its safety for procedural sedation in neonates is controversial. The aim of this study was to perform a prospective propofol dose-finding study with pharmacodynamic (PD) assessment during (semi-)elective intubation in neonates.
Methods: Patients were stratified in 4 groups by postmenstrual and postnatal age. The first patient in each group received 1 mg/kg intravenous propofol bolus. Dosing for the next patient was determined using the up-and-down method. Propofol ED50 doses [effective dose for successful intubation (as well as extubation in INSURE -intubation, surfactant, extubation-cases) in 50% of patients] were calculated, with simultaneous assessment of clinical scores, continuous vital sign
monitoring and propofol blood ooncentrations (3 and 12h after dosing).
Results: Thirty-five neonates (weight 540-3290 g) were included. Using initial and total propofol dose ranges of 0.5-2 and 0.5-4.5 mg/kg respectively, median propofol ED50 range for pretern neonates regional cerebral (rSc02) oxygen saturation was documented. Variability in MABP, Sa02 and rSC02 was not explained by weight, age or prepafol concentrations.
Conclusions: Low propofol doses sufficiently sedate neonates for intubation, but clinical recovery takes time and is accompanied by permissive hypotension. Propafol ED50 doses are provided and need integration in a prospective validation approach. Finally, feasibility of continuous monitoring for neonatal pharmacodynamic research was demonstrated.

To what extent does the vancomycin assay contribute to the variability in vancomycin concentration estimates in neonates?
J. Samardzic, A.Smits, V. Cosset. I. Soldatovic, M. Bajcetic, J. N. van den Anker, K. Allegaert

Introduction: Vancomycin, a glycopeptide antibiotic, is frequenUy used for late onset sepsis (LOS) and catheter-related infection. Larger inter- and intra-patient variability, combined with a narrow therapeutic index, warrants therapeutic drug monitoring (TDM). However, large inter-individual variability in
PK parameters in neonates is documented, only partly explained by covariates such as weight, age or serum creatinine (1,2). In the current study, we focus on the potential impact of between assay differences for vancomycin (3) on the variability in its concentration in a single neonatal intensive care unit (NICU).
Methods: Vancomycin TDM observations of neonates and young infants treated with intravenous vancomycin, mainly for (suspected) LOS (ie, > 72 hours after birth), in the Leuven NICU, Belgium, between June 2011 and December 2014. Our patient population, consists of (pre)term neonates, inborn or transferred, in need of specialized care related to prematurity, infections, perinatal asphyxia, congenital diseases (eg, surgery for cardiopathy, congenital diaphragmatic hernia, or esophageal atresia), or other diseases. Clinical characteristics at birth, as well as characteristics at the moment of TDM were extracted from the patient files. We aimed to document early vancomycin exposure, therefore only first trough levels were included. Serum vancomycin assay was performed either with a particle-enhanced turbidimetric inhibitionimmunoassay method (Siemens Dimension; Dade Behring, Deerfield, Illinois – PETINIA) or with an enzyme multiplied immunoassay technique (Cobas c702; Roche Diagnostics, Basel, Germany – CaSAS). The data were analyzed by Chi-square test, t test and Mann-Whitney U test. Linear Mix Model was used to assess significant differences between groups, when adjusting for confounding factors. Data were analyzed in SPSS 20.0 (IBM corp.), p-value Results: In total, 564 vancomycin TDM observations, 311 assayed with PETINIA and 253 with COBAS, were Included. Both cohorts had comparable clinical characteristics (median [min-max] current weight 2150 [420-5000] grams for PETINIA vs. 2120 [500-5840] grams for COBAS. and median postmenstrual age 35 [25-58] weeks for PETINIA vs. 35 [25-51] weeks for COBAS). We determined the significant difference between the vancomycin concentrations using two different immunoassays: PETINIA vs. COBAS (F=17.971; p<0.001). When adjusting for current body weight and postmenstrual age, the major covariates associated with vancomycin serum trough levels in neonates, the difference in vancomycin concentration between cohorts was statisticaJly significant (F=17.076, p<0.001, F=18.951,
p<0.001, respectively). Overall, immunoassays PETINIA and COBAS signifiCantly differed by vancomycin concentrations when adjusting for covariates, and the mean difference for vancomycin concentration was 2.167 mg/l. Conclusion: The present study confirms the impact of assays on the variability in vancomycin concentration in neonates in a single NICU. Comparison between these two immunoassays showed a mean proportional differences >20%. Therefore, it is iImportant to know how the vancomycin is measured when interpreting results, and particulariy the transferability of vancomycin results between the laboratories has to be interpreted with caution.

Augmented renal clearance implies a need for increased amoxicillin/clavulanate dosing in critically ill children
Pieter De Cock, Joseph Standing, Charlotte Barker, Annick de Jaeger, Mieke Carlier, Evelyn Dhont, Alain Verstraete, Joris Delanghe, Hugo Robays, Peter De Paepe

Background: Amoxicillinlclavulanate is commonly used to treat community-acquired infections on the pediatric intensive care unit. Few data are available to guide dosing in this vulnerable population.
Methods: This prospective pharmacokinetic study enrolled patients admitted to the pediatric intensive care unit in whom intravenous amoxicillin-clavulanate was indicated (25-35 mg/kg q6h). Serial blood samples were obtained following the first and steady-state doses and amoxicillin/clavulanate concentrations were measured by a validated high-pressure liquid chromatography (HPLC}-tandem mass spectrometry method. Population pharmacokinetic analysis and Monte Carto simulations were conducted using NONMEM 7.3.
Results: Three hundred twenty-five amoxicillin and 151 clavulanate blood samples were collected from 50 patients with a median age of 2.58 years (range: 0.08-15 years). A 3-compartment model for amoxicillin and a two-compartment model for clavulanate best described the data, in which allometric weight scaling and maturation functions were added a priori to scale for size and age. In addition, serum Cystatin C (sCysC) was a marker for renal function and concomitant
treatment with vasopressors were identified to have a significant influence on amoxicillin clearance. The typical population values of clearance for amoxicillin and clavulanate were 17.97 L/H/70 kg (95% CI:15.33-21.30 L/H/70 kg) and 12.20 L/H/70 kg (95 % CI:10.54-14.55 L/H/70 kg), respectively. Four hourly doSing of 25 mg/kg (based on the amoxicillin component) was required to achieve 40% of the dosing interval for amoxicillin concentrations to be above MIC, and for clavulanate levels to be maintaIned above 2 mg/l. For patients with augmented renal function a 1 hour infusion was preferable to bolus dosing to achieve the therapeutic target.
Conclusions: Current dosing regimens result in subtherapeutic concentrations In the early period of sepsis due to augmented renal clearance, which risks treatment failure in critically ill children.

Possible confounders in the reported association between autism spectrum disorder (ASO) and exposure to selective serotonin reuptake inhibitors (SSRls) during pregnancy
Pauline De Bruyne, Eran Barzilayl, Gideon Koren

Background: Autism has been in the forefront of public concern because of reported increase in prevalence and growing interest in the role of environmental risk factors in autism. A recent meta-analysis by Man at al. (2015) reported an increased risk of ASO in children of mothers exposed to SSRls during pregnancy (adjusted OR 1.81, 95% CI 1.47-2.24). However, association may not imply a causal relation between SSRI exposure and ASO. We hypothesize that undertying
disease might have confounded the published result.
Materials and methods: A literature review was performed in order to identify possible confounders in the reported association. The list of search terms included but was not limited to following terms: ‘Pregnancy’, ‘maternal’, depression’, ‘child behaviour’, ‘health care seeking behaviour’.
Results: Retrieved articles were classified in following four domains of possible confounders: 1) direct link between depression and ASO, 2) effect of depression on interaction with the child, 3) effect of depression on other risk factors of ASO and 4) ascertainment bias. In the last domain, we examined the effect of depression on the way mothers perceive and report on the behaviour of their child and the effect of maternal depression on healthcare seeking behaviour.
Analysis suggests that there are important merits to all those four domains.
Conclusion: Because of obvious ethical reasons, research on exposure during pregnancy is mostly restricted to systematic review and meta-analysis of observational studies. Although this has resulted in a treasury of information, possible confounders must be taken into account when interpreting the results.

SAFE-PEDRUG: a new strategy for paediatric drug research
Pauline De Bruyne, Kevin Meesters, Johan Vande Walle

Background: Drug evaluation in children is stimulated by initiatives of the Regulatory Authorities; in Europe by the ‘Paediatric Regulation’. As stated in this Regulation, Paediatric Investigational Plans must be submitted to the Paediatric Committee around the end of Phase I adult trials. However, the proposed paediatric trials tend to be amended frequently and postponed to the end of the drug evaluation process, as they are largely based on extrapolations of results of
adult trials.
Materials and methods: Experts in paediatrics, pharmaceutical sciences, veterinary medicine and ethics (of three Belgian universities) collaborated to develop a research consortium that will focus mainly on generating paediatric pharmacokinetic and pharmacodynamic (PK/PD) knowledge before the actual human trials are performed. National and intemational stakeholders (including Industry, Regulatory Authorities, and Patient Organisations) support this consortium in the
valorisation of results.
Results: The above-mentioned networking resulted in the SAFE-PEDRUG project, funded by the Agency for Innovation by Science and Technology (Flanders). This program will explore the value of the porcine juvenile animal model and PK modelling (physiologically-based pharmacokinetic modelling) in providing prior paediatric PK/PD-knowfedge. For the evaluation of this approach, three case compounds were selected: desmopressin, lisinopril, and f1uoroquinolones. The results of the models are plotted against human paediatric data. Furthermore, PK/PD in neonates and critically ill children will also be explored.
Conclusion: A close collaboration of experts and stakeholders is mandatory for the future of paediatric pharmacology. Exchange of ideas and knowledge can help to tailor paediatric clinical trials to the PK/PD-characteristics and needs of children.

Prospective validation of a model-based dosing regimen for amikacin in neonates: feasible and relevant
Anne Smits, Roosmarijn De Cock, Karel Allegaert, Sophie Vanhaesebrouck, Meindert Danhof, Catherijne Knibbe’

Introduction: A neonatal amikacin dosing regimen was previously developed based on a population pharmacokinetic model. The aim of the current study was to prospectively validate this model-derived dosing regimen.
Methods: First, early (before and after second dose) therapeutic drug monitoring (TDM) observations were evaluated for achieving target trough 24 mgl/L) levels. Secondly, observed concentrations were compared with model-predicted concentrations, whereby the results of an NPDE (normalized prediction distribution error) were considered as well. Subsequently, Monte Carlo simulations were performed. Finally, remaining causes limiting amikacin predictability (prescription errors and disease characteristics of outliers) were explored.
Results: In 579 neonates [median (range) birth bodyweight 2285 (420-4850) g, postnatal age 2 (1-30) days, geslational age 34 (24-41) weeks], 90.5% of early peak levels reached 24 mgl/L and 60.2% of trough levels was 24 mg/L were reached in almost all patients. Trough values documented in 78-100% and 45-96% of simulated cases, respectively, when ibuprofen was coadministered or not. Suboptimal trough levels were found in patient subgroups with postnatal age 2000g.
Conclusions: Prospective validation of a model-based neonatal amikacin dosing regimen resulted in optimized peak and trough concentrations in almost all patients. Adapted dosing for patients with suboptimal trough levels was proposed. Besides improving dosing individualization, feasibility and relevance of neonatal prospective validation studies was demonstrated.

Unintentional overdosing of intravenous paracetamol in neonates: where is the toxicity?
Barbara Bosch, Kristina Casteels. Karel Allegaert

Introduction: Paracetamol is a readily available antipyretic and analgesic, widely used to treat mild to moderate pain. Unintentional overdosing in neonates occurs, but so far only single case reports have been published. Based on an own case and a bibliographic search, we review the safety and tolerance of unintentiontal overdosing of intravenous paracetamol in neonates.
Material and methods: A bibliographic search in PubMed and EMBASE using key words: “Pharmacokinetics paracetamol neonate”, “Metabolism paracetamol neonate” and “Effects paracetamol neonate” was performed.
Results: Thirty cases of neonatal iv paracetamol intoxication were reported. Overall, the reported number remains limited, but even 10-fold drug errors only rarely result in significant morbidity or mortality. In accidental overdosing only one case of relevant hepatic toxicity has been reported.
Conclusion: The reported cases of unintentional paracetamol overdosing in neonates suggests a good safety profile and a population specific tolerance. Acetylcysteine administration is recommended, but the prognOSis seems to be better in neonates.

How safe Is on-label drug use in paediatrics? The case of first generation H1-antihistamines
Pauline De Bruyne, Koen Boussery, Thierry Christiaens, Els Mehuys, Myriam Van Winckel

Background: For obvious reasons, much attention has recently been paid to off-label prescriptions in paediatrics. However, on-label prescribing can cause health issues too: we discuss the case of first generation H1-antihistamines (FGAs). These have been in use for over 70 years, for a variety of indications such as relief of allergic conditions, cough and insomnia.
Materials and methods: The FGAs were listed using their International Nonproprietary Names (INN). For each formulation, the informalion of the Summary of Product Characteristics issued in five selected European countries (Belgium, France, Germany, the Netherlands and United Kingdom) was collected. This was plotted against the published evidence on efficacy and safety of each FGA.
Results: 16 different FGAs are currently marketed in single-drug oral preparations in the evaluated countries. When investigating each drug separately, a huge variability in labelled indications, licensing age for paediatric use, and availability characteristics in the different countries is observed. Most of the indications are not supported by evidence from published clinical trials.
Conclusion: Both health care professionals and consumers generally assume that all approved H1-antihistamines have been shown to be efficacious and safe, but many in this class – in particular those introduced before 1985 – have not been optimally studied. This might explain the inconsistencies in indications and licensing ages of the evaluated drugs in different countries. Moreover, many of the antihistamines are sold over the counter, which may contribute to overuse.
Such overuse can be a serious problem, as sedation is a known side effect of all FGAs.

Use of Fluoroquinolones in Hospitalized Children, preliminary report of a chart review in a Belgian university children’s hospital
Kevin Meesters, Pauline De Bruyne, Reiner Mauel, Johan Vande Walle

According to international guidelines, f1uoroquinolones (FQ) should only be prescribed to children when there is no alternative antibiotic. FQ resistance is a rapidly growing problem worldwide. We hypothesize that FQ are frequently prescribed off-label in children. To confirm this hypothesis, we analyzed FQ prescriptions for hospitalized children in a Belgian university hospital.
Method: We reviewed all prescriptions of FQ for children up to 17 years of age who were hospitalized at Universitair Ziekenhuis Brussel, a Belgian university children’s hospital, in the period 2010-2013. Patient characteristics, indication for the FQ prescription and microbial cultures were obtained from the medical file. The study was approved by the institutional review board.
Results: As we foresee to finish our data analysiS by the end of April 2015, we present the results of our interim analysis here. Until now, a total of 178 FQ prescriptions in 79 children were analyzed. The majority of children had major comorbidities such as childhood cancer, cystic fibrosis or inflammatory bowel disease. FQ prescription was based on a microbial culture in 15.4% of cases. Frequent indications for FQ prescription were Pseudomonas eradication in cystic fibrosis patients, long term antibiotic prophylaxis in neutropenic patients and wound infections. Prescribed daily doses and consumed daily doses varied widely, even for the same indication. Concomitant medications were common and included mainly other antibiotics, steroids and chemotherapeutics.
Conclusion: FQ were used as ‘reserve antibiotic,’ and so on-label, in a minority of all FQ prescriptions for hospitalized children.

European Workshop on Neonatalogy
Location: Landskrona, Sweden
Date: 14/06/2015-17/06/2015

Drug disposition in neonates: cross talk between developmental physiology and pharmacology
Allegaert K

Tramadol disposition in early infancy illustrates in vivo drug transporter activity.
Allegaert K

PAGE Meeting
Location: Hersonissos
Date: 02/06/2015-05/06/2015

Bioequivalence of desmopressin in children: a population pharmacokinetic study
Robin Michelet, Pauline De Bruyne, Lien Dossche, Johan Vande Walle, Jan Van Bocxlaer, An Vermeulen

Introduction: Off-label use of drugs in the pediatric population is widespread: 50-90% of drugs are not tested in children [1]. The project SAFE-PEDRUG aims to provide new medical and ethical guidelines for conducting clinical trials in children, based on a rational combination of bottom-up and top-down investigations. Desmopressin (DDAVP), one of the drugs under study, is a synthetic vasopressin analogue used in nocturnal enuresis treatment. Two formulations, a tablet (TAB) and a lyophilisate (MELT), exist of which the bio-equivalence has been established in adults but not in children. This pilot study investigates how the drug product influences the pharmacokinetics and provides suggestions for subsequent studies.

Methods: Earlier published data on 22 children (mean age 12.7 y and mean weight 50.1 kg) were included in the study. Blood samples were taken 1h, 2h and 6h after both TAB and MELT dosing at 200 and 120 µg, respectively. Dosing events were 2 weeks apart and patients received a standardized meal before administration [2]. In addition, an available part of historical data (28 patients, 1-3 samples per patient) from Osterberg et al. [3] were also included in the analysis.

A 1-compartment model with first order absorption was fitted to the data using NONMEM (v. 7.3, [4]). Covariates were selected through one-by-one screening to construct a full model, followed by backward deletion. The final model goodness-of-fit (GOF) was evaluated by means of diagnostic tools and a sensitivity analysis (SA) was performed to evaluate the sampling design.

Results: The popPK model was able to describe DDAVP plasma concentrations adequately as is shown by the different diagnostics. The NPDE distribution did not significantly differ from the normal distribution and the basis GOF plots only showed a slight bias at low concentrations. In this model, formulation and fasted/fed state were included as significant covariates on F1 and body weight on distribution volume. MELT was found to be 1.321 times more available as TAB, while being fasted increased the bioavailability 2.01 times. SA showed optimal sampling times to be between 0.5 and 1.5, and at 5 hours.

Conclusions: For the first time in children, the difference in relative bioavailability between the two DDAVP drug products has been proven to be significant. Furthermore, sampling times for a further study were suggested which should result in more informative data and consequently generate a more reliable model.

Population cefazolin pharmacokinetics before, during and after cardiopulmonary bypass in children undergoing cardiac surgery
Pieter De Cock, Hussain Mulla, Karen Jacobs, Kim Vanderburght, Sarah Desmet, Brett McWhinney, Jacobus Ungerer, Filip De Somer, Annelies Moerman, Hugo Robays, Katrien Francois, Peter De Paepe

Objectives: Scarce data are available to guide cefazolin dosing in children undergoing cardiac surgery with cardiopulmonary bypass[1,2]. The objective of this trial is to derive a model-based dosing regimen for cefazolin in this patient population.

Methods: 56 infants and children were included (median age: 0.75 years; range:0.01-15 years) and received following intravenous dosing regimen: 25 mg/kg 30 minutes before surgical incision, just before start weaning of cardiopulmonary bypass, 8 hours after the 2nd dose and 8 hours after the 3rd dose. Blood, auricle and subcutaneous fat tissue samples were collected before, during and/or after cardiopulmonary bypass. NONMEM ®v7.2 was used for population PK modelling and covariate analysis of plasma and tissue data. Internal validation of the final model was performed using a non-parametric bootstrap and Visual Predictive Check (VPC).

Results: A two compartment model best described bound and unbound plasma concentrations. The effect of cardiopulmonary bypass was modelled using a separate compartment. The relationship between bound and unbound concentrations was described by a saturable binding model, and where plasma albumin levels was a significant covariate on maximum binding capacity (Bmax). Weight was identified as a significant covariate on all plasma and tissue clearance and volume parameters using allometric scaling. Implementation of estimated Glomerular Filtration Rate (eGFR) as a covariate on plasma clearance further improved the model.

Conclusions: The proposed model adequately describes cefazolin plasma and tissue pharmacokinetics in infants and children undergoing cardiac surgery with cardiopulmonary bypass. In a next step, Monte Carlo simulations will be performed to optimize dosing in this vulnerable patient population.

CoPedia Meeting
Location: Budapest
Date: 16/04/2015-19/04/2015

Therapeutic drug monitoring in neonates: aminoglycosides and vancomycin
Allegaert K

Developmental pharmacology = developmental physiology
Allegaert K, van den Anker J

Systems Pharmacology Symposium
Location: Noordwijkerhout
Date: 22/04/2014-25/04/2014
Physiologically Based Pharmacokinetic Modeling and Simulation Can Aid Pop-PK Model Building in Estimating the CYP2D6 Maturation Clearance in Early Life
Huybrecht T’jollyn, Jan Snoeys, Geert Mannens, Achiel Van Peer, Karel Allegaert, Koen Boussery, Jan Van Bocxlaer, An Vermeulen

Tramadol is a centrally acting analgesic drug with weak opioid activity and is prescribed in neonates and young infants after surgical or medical interventions, where it is administered intravenously [loading dose 2–3 mg kg-1 over 30 min, followed by continuous administration of tramadol hydrochloride 5–8 mg kg-1 (24 h)-1] [1] . Tramadol’s CYP2D6 metabolite, O-desmethyl tramadol (ODT), has a µ-opioid activity 200 times that of tramadol. Consequently, CYP2D6 polymorphisms and isoform specific ontogeny will influence ODT formation and hence the achieved µ-opioid effect. Therefore, knowledge on the maturation of CYP2D6 will inform and aid neonatologists in administering an adequate dose of tramadol in neonates and young infants.

In a previous study three different clearance models were set up in order to investigate the performance of bottom-up PBPK modeling and simulation in predicting adult PK of tramadol. In this setup, a retrograde model was constructed and served as a reference model in the bottom-up modeling process. In short, published in vivo data of tramadol total clearance and the influence of CYP2D6 polymorphisms on the metabolic clearance were used to derive CLint values on the CYP450 isoform level. Therefore, this retrograde model adequately predicts the total clearance and CYP2D6 contribution in the hepatic clearance of tramadol in adults. Pediatric simulations with this retrograde model account for ontogeny of different enzymes, altered tissue volumes, blood flows, and tissue composition depending on the chosen age range of the virtual population. By overlaying the predicted pediatric clearance values by the retrograde model with the observed pediatric clearances estimated by a NONMEM analysis in 57 neonates and young infants[1], large discrepancies are found between these PBPK predicted and the popPK estimated clearance values. Based on all current knowledge about CYP2D6 and liver maturation patterns, we could not explain the much faster CYP2D6 maturation seen in the popPK estimated clearance values. However, because we had access to the raw data and even some additional urine data, we were able to do a one-by-one fitting in WinNonlin for 9 out of the 57 subjects and found out that by adding the urine data to the popPK model, the estimated CYP2D6 clearance values became much lower and essentially matched our PBPK predicted CYP2D6 clearance values.

In conclusion, a major assumption underlying physiologic scaling is that clearance pathways in children are the same as in adults, and so adult PBPK models should have a good predictive accuracy in order to make useful pediatric simulations[2]. Furthermore, the current mechanistic knowledge concerning CYP2D6 ontogeny and liver maturation, which is implemented in the current PBPK model, helped in determining an accurate estimate of CYP2D6 maturation in tramadol metabolism in early life. As a consequence, pediatric PBPK modeling and simulation can aid in implementing a correct CYP2D6 maturation function in pediatric popPK model building.

Knowledge For Growth Meeting
Location: Ghent
Date: 30/05/2013

Quantitative IVIVE-Linked Pediatric PBPK Predictions: Case Study Tramadol
Huybrecht T’jollyn, Pieter Colin, Jan Snoeys, Jan Van Bocxlaer, Achiel Van Peer, Karel Allegaert, Geert Mannens and Koen Boussery

Historically, in vitro enzyme kinetic experiments were conducted to have a rough idea on the intrinsic metabolic clearance of liver-derived in vitro systems without a physiologically relevant focus on this preclinical part of the R&D process. However, with the recent shift towards the use of these kinetic data for quantitative PBPK modeling & simulation, the experiments for determination of enzyme kinetic parameters should be performed, in addition to linearity assessment, with concentrations mimicking the in vivo obtained concentrations as closely as possible, ensuring ‘extrapolatibility’ from in vitro to in vivo pharmacokinetics (avoid rubbish in-rubbish out principle).
This study represents the ‘bottom-up’ scaling of in vitro enzyme kinetic data of tramadol, chosen as a representative probe for multi CYP450 involvement, using the IVIVE-linked PBPK modeling and simulation platform Simcyp®. In essence, in vitro enzyme kinetic data of a test drug is mechanistically scaled to in vivo pharmacokinetics, using in vitro-in vivo extrapolation (IVIVE) principles in a physiologically-based pharmacokinetic (PBPK) modeling and simulation environment. Enzyme kinetics of tramadol were investigated in pooled human liver microsomes and recombinant CYP enzyme systems. A range of concentrations was tested in either system to determine the observed in vitro clearance vs. substrate concentration. Non-linear models that best described the kinetic data were constructed in R to extract intrinsic clearance (CLint), Km, and Vmax parameters. In turn, these are used as input for IVIVE-PBPK models in order to predict in vivo pharmacokinetics. Three different in vitro input models were investigated: model 1 is based on intrinsic clearance (CLint) values from HLM corrected for specific CYP450 contributions from a chemical inhibition assay; model 2 is based on CLint values obtained in recombinant enzyme systems; model 3 is based on CLint values from HLM corrected for specific CYP450 contribution by CLint values obtained from the recombinant enzymes. The outcome of every model was validated against tramadol in vivo pharmacokinetic data from literature. Model 3 gave the best predictions in terms of visual predictive check, median fold error (MFE) and variability fold error (VFE) on the predicted clearance. Predictions were considered as good clinical estimates, being between 0.8- and 1.25-fold of the observed clearance.
The IVIVE-linked PBPK approach proved to be a strong integrative approach, combining in vitro, as well as in vivo and in silico data, to provide good clinical estimates of the in vivo PK of tramadol in adults, and gain mechanistic insight in relevant disposition covariates at hand.