Population pharmacokinetics of modafinil and its acid and sulfone metabolites in Chinese males.

BACKGROUND: Modafinil is a psychostimulant used to treat excessive sleepiness. The aim of this study was to develop a population pharmacokinetic model of modafinil and its major metabolites in Chinese male adults and to identify covariates that predict variability in disposition. METHODS: Eighty healthy volunteer subjects were randomized to 4 oral dose groups: 3 doses of 50 mg of modafinil, 3 doses of 100 mg of modafinil, 2 doses of 200 mg of modafinil plus 1 dose of placebo, or 3 doses of placebo (each dose given 8 hourly). Blood samples were collected up to 58 hours post-first dose for plasma concentrations of modafinil and its metabolites. Pharmacokinetic data analyses were performed using noncompartmental and compartmental approaches. The population pharmacokinetic study was conducted using the nonlinear mixed-effects model software, NONMEM, and validated using the bootstrap, crossvalidation and visual predictive check approaches. RESULTS: Data were best described by a 5-compartment model: 2 compartments for modafinil (first-order absorption from gut compartment) and 1 each for modafinil acid and modafinil sulfone. A covariate analysis identified body weight as influencing volumes of the central and peripheral compartments for modafinil. All the parameters were estimated with good precision (relative standard error < 39%). The visual predictive check found that the final pharmacokinetic model adequately predicted observed concentrations of all 3 molecular species. The authors developed dosing schedules to achieve minimum trough plasma modafinil concentrations of 3 mcg/mL. CONCLUSIONS: A robust population pharmacokinetic model for modafinil and its metabolites was developed for the first time. Based on this model, individualized dosing based on weight is now possible.