Population Pharmacokinetics of Modafinil and Its Acid and Sulfone Metabolites in Chinese Males

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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.

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