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Population pharmacokinetics of valproic acid in pediatric patients with epilepsy: considerations for dosing spinal muscular atrophy patients.

ABSTRACT: Valproic acid (VPA) dosing strategies used in recent clinical trials in patients with spinal muscular atrophy (SMA) have utilized a paradigm of monitoring trough levels to estimate drug exposure with subsequent dose titration. The validity of this approach remains uncertain and could be improved by understanding sources of pharmacokinetic variability. A population pharmacokinetic analysis of VPA in pediatric patients with epilepsy was recently performed. The pooled data set included 52 subjects with epilepsy, ages 1 to 17 years, who received intravenous and/or various oral formulations. The data was best fit by a 2-compartment model; inclusion of age and weight reduced intersubject variability for clearance (41%), central volume (70%), and peripheral volume (42%) over the base model. The final model for clearance and volume parameters was clearance = 0.854 · (weight/70)(0.75); central volume of distribution = 10.3 · (weight/70)(1.0) · (age/8.5)(-0.267); peripheral volume of distribution = 4.08 · (weight/70)(1.0); and intercompartmental clearance = 5.34 · (weight/70)(0.75). Application of the model to data from a clinical trial in SMA patients suggests altered kinetics, perhaps based on underlying physiologic differences such as alterations in lean body mass. Future studies in SMA should incorporate modeling and simulation techniques to support individualized dosing and further assess if additional patient-specific factors necessitate alternative dosing strategies.

SUBMITTER: Williams JH

PROVIDER: S-EPMC3345311 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Population pharmacokinetics of valproic acid in pediatric patients with epilepsy: considerations for dosing spinal muscular atrophy patients.

Williams Jason H JH Jayaraman Bhuvaneswari B Swoboda Kathryn J KJ Barrett Jeffrey S JS

Journal of clinical pharmacology 20111213 11

Valproic acid (VPA) dosing strategies used in recent clinical trials in patients with spinal muscular atrophy (SMA) have utilized a paradigm of monitoring trough levels to estimate drug exposure with subsequent dose titration. The validity of this approach remains uncertain and could be improved by understanding sources of pharmacokinetic variability. A population pharmacokinetic analysis of VPA in pediatric patients with epilepsy was recently performed. The pooled data set included 52 subjects ...[more]

PMID: 22167565

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Project description:UNLABELLED:Preliminary in vitro and in vivo studies with valproic acid (VPA) in cell lines and patients with spinal muscular atrophy (SMA) demonstrate increased expression of SMN, supporting the possibility of therapeutic benefit. We performed an open label trial of VPA in 42 subjects with SMA to assess safety and explore potential outcome measures to help guide design of future controlled clinical trials. Subjects included 2 SMA type I ages 2-3 years, 29 SMA type II ages 2-14 years and 11 type III ages 2-31 years, recruited from a natural history study. VPA was well-tolerated and without evident hepatotoxicity. Carnitine depletion was frequent and temporally associated with increased weakness in two subjects. Exploratory outcome measures included assessment of gross motor function via the modified Hammersmith Functional Motor Scale (MHFMS), electrophysiologic measures of innervation including maximum ulnar compound muscle action potential (CMAP) amplitudes and motor unit number estimation (MUNE), body composition and bone density via dual-energy X-ray absorptiometry (DEXA), and quantitative blood SMN mRNA levels. Clear decline in motor function occurred in several subjects in association with weight gain; mean fat mass increased without a corresponding increase in lean mass. We observed an increased mean score on the MHFMS scale in 27 subjects with SMA type II (p<or=0.001); however, significant improvement was almost entirely restricted to participants <5 years of age. Full length SMN levels were unchanged and Delta7SMN levels were significantly reduced for 2 of 3 treatment visits. In contrast, bone mineral density (p<or=0.0036) and maximum ulnar CMAP scores (p<or=0.0001) increased significantly. CONCLUSIONS:While VPA appears safe and well-tolerated in this initial pilot trial, these data suggest that weight gain and carnitine depletion are likely to be significant confounding factors in clinical trials. This study highlights potential strengths and limitations of various candidate outcome measures and underscores the need for additional controlled clinical trials with VPA targeting more restricted cohorts of subjects. TRIAL REGISTRATION:ClinicalTrials.gov.

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Population pharmacokinetics of valproic acid in pediatric patients with epilepsy: considerations for dosing spinal muscular atrophy patients.

Publications

Population pharmacokinetics of valproic acid in pediatric patients with epilepsy: considerations for dosing spinal muscular atrophy patients.

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