Quantitative Assessment of CYP2C9 Genetic Polymorphisms Effect on the Oral Clearance of S-Warfarin in Healthy Subjects

Background Genetic polymorphisms in CYP2C9 account for 10-20% of the variability in warfarin dose requirement. As such CYP2C9 genetic polymorphisms are commonly included in algorithms aimed to optimize warfarin therapy as a way to account for variability in warfarin responsiveness that is due to altered pharmacokinetics. However, most of the currently available pharmacokinetic data were derived from studies among patients on chronic warfarin therapy and therefore suffer from the confounding effects of disease states and drug interactions. Objective The purpose of the present study was to provide an accurate quantitative estimate of S-warfarin oral clearance (CLS) among healthy subjects carrying different CYP2C9 genotypes. Methods Single dose of warfarin was administered to 150 non-smokers, age (mean +/- SD) 23.3 +/- 4.5 years, 60% male, non-obese, healthy subjects. Blood samples were taken for up to 168 h and urine was collected over the entire study period. Results Compared with carriers of the wild-type CYP2C9*1/*1 genotype (n = 69), CLS was reduced by 25, 39 and 47% among heterozygote for CYP2C9*2 (n = 41) CYP2C9*3 (n = 26) and carriers of 2 variant alleles (n = 14), respectively (p < 0.001). The corresponding decrease in the formation clearance of 6 and 7 S-hydroxy-warfarin was 45, 65 and 75%, respectively (p < 0.001). Conclusions The current study provides an estimate concerning the effect of CYP2C9 polymorphisms on S-warfarin pharmacokinetics among healthy subjects. As such it is free of the confounding effects of disease states and drug interactions. Further research is needed to evaluate whether the incorporation of quantitative data obtained in the present study into pharmacogenetic warfarin algorithm may enhance its precision.