• Rui Nagai, Minami Ohara, Larisa H Cavallari, Katarzyna Drozda, Shitalben R Patel, Edith A Nutescu, Minoli A Perera, Wenndy Hernandez, Naoko Kaneko, Manabu Hibiya, and Harumi Takahashi.
• Department of Biopharmaceutics, Meiji Pharmaceutical University, Kiyose, Tokyo 204 8588, Japan.
• Pharmacogenomics. 2015 Jan 1;16(3):217-25.

AimThis study attempted to identify predictors of S-warfarin clearance (CL[S]) and to make a pharmacokinetic evaluation of genotype-based dosing algorithms in African-Americans.MethodsUsing plasma S-warfarin concentration (Cp[S]) at a steady state and eight SNPs previously shown to influence warfarin dose in African-Americans, CL(S) and its predictors were estimated by population pharmacokinetic analysis in 60 African-Americans. The time courses of Cp(S) following either the loading dose or maintenance dose were simulated using the population pharmacokinetic estimates.ResultsCYP2C9*8 and body surface area or body weight were predictors of CL(S) (-30 and -5% per -0.1 m(2)/-10 kg reduction in CL[S], respectively) in African-Americans. Simulations of Cp(S) showed that Cp(S) at steady state was 1.4-times higher in patients with CYP2C9*8 than in those with CYP2C9*1/*1, irrespective of the algorithm for loading dose or maintenance dose.ConclusionAfrican-Americans possess independent predictors of CL(S), possibly leading to a prediction error of any dosing algorithm that excludes African-specific variant(s). Original submitted 3 September 2014; Revision submitted 3 November 2014.

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