Pharmacokinetics of carisbamate (RWJ-333369) in healthy Japanese and Western subjects
Summary
Purpose: To compare the pharmacokinetics of carisbamate (RWJ-333369) in healthy Japanese and Western adults, and to comparatively assess carisbamate safety and tolerability between the two populations.
Methods: An open-label study was conducted in 24 Japanese and 24 Caucasian healthy subjects. Subjects received a single oral dose of 250 mg carisbamate on day 1 followed by a 3-day washout period; twice-daily dosing of 250 mg carisbamate on days 5–8; subsequently, 500 mg on days 9–12 and a single dose of 500 mg on day 13. Plasma samples were collected for a pharmacokinetic analysis on days 1, 8, and 13. Plasma and urine samples were analyzed for carisbamate and its urinary metabolites by liquid-chromatography-mass-spectrometry.
Results: Following a single dose, carisbamate Cmax and area under the curve (AUC) geometric mean ratios were 16.4% and 28.8% higher in Japanese than in Caucasians, respectively; these differences were statistically significant and their 90% confidence intervals (CIs) fell outside of the 80–125% limits, which are considered not to be of clinical significance. With dose–body weight normalization, Cmax and AUC were similar in Japanese and Caucasian subjects and the 90% CIs were within the 80–125% boundaries. Carisbamate was well tolerated, and its mean oral clearance and half-life were similar in both groups, ranging from 35.1–41.4 ml/h/kg and 11.5–12.8 h.
Discussion: Carisbamate plasma exposure (AUC) and Cmax in Japanese subjects is ∼20–25% higher than in Caucasians due to a higher mg/kg dose. After body weight normalization, carisbamate pharmacokinetics was similar between Japanese and Caucasian subjects following single and multiple dosing, and showed the same dose proportionality.
