Population pharmacokinetics of oxcarbazepine and its monohydroxy derivative in epileptic children

Area of Science:

• Pharmacokinetics and Drug Metabolism
• Pediatric Pharmacology
• Clinical Pharmacy

Background:

• Oxcarbazepine is an antiepileptic drug (AED) whose efficacy is primarily mediated by its active metabolite, monohydroxy derivative (MHD).
• Accurate dosing in pediatric populations is crucial for achieving therapeutic trough concentrations (Ctrough) of MHD, ranging from 3-35 mg/l.
• Population pharmacokinetic (PopPK) modeling provides a framework for understanding drug behavior in diverse patient groups, including children.

Purpose of the Study:

• To develop a parent-metabolite population pharmacokinetic model for oxcarbazepine in pediatric patients.
• To assess the consistency of current pediatric dosing recommendations with the target MHD Ctrough range.
• To identify potential dosing adjustments for specific pediatric subgroups.

Main Methods:

• Analysis of 279 plasma samples from 31 epileptic children (aged 2-12 years) following single-dose oxcarbazepine administration.
• Development of a two-compartment oxcarbazepine and one-compartment MHD pharmacokinetic model using Monolix 4.3.2 software.
• Monte Carlo simulations to determine the probability of achieving target MHD Ctrough across a range of pediatric doses (10-90 mg/kg/day).

Main Results:

• The developed parent-metabolite model accurately described oxcarbazepine and MHD pharmacokinetics, incorporating allometric scaling by body weight.
• Concomitant use of enzyme-inducing antiepileptic drugs (EIAEDs) increased MHD clearance by 29.3%.
• Simulations indicated that 50-kg children without EIAEDs may require lower doses (20-30 mg/kg/day) than recommended (30-45 mg/kg/day), while 10-kg children with EIAEDs might need higher doses (90 mg/kg/day) than the maximum recommended (60 mg/kg/day).

Conclusions:

• The population pharmacokinetic model supports current oxcarbazepine dosing guidelines for most pediatric patients.
• Specific adjustments are warranted for 10-kg children on EIAEDs and 50-kg children not on EIAEDs to optimize MHD exposure.
• This model aids in refining pediatric oxcarbazepine dosing strategies for improved seizure control and safety.