Abstract
Based on in vitro rat and human hepatocyte uptake studies showing inhibition of warfarin uptake in the presence of the nonspecific organic anion-transporting polypeptide (OATP) inhibitor rifampin, a clinical study was conducted in 10 healthy volunteers to examine the in vivo relevance of OATP hepatic uptake on the pharmacokinetics of warfarin. In a randomized, single-dose, two-period, crossover design, subjects received a 7.5-mg dose of warfarin, either alone or immediately following a 600-mg intravenous dose of rifampin. Rifampin did not significantly alter the R- or S-warfarin area under the concentration-time curves (AUCs) from 0 to 12 h (period of hepatic OATP inhibition by rifampin) or the maximum plasma concentration (C(max)) value. AUC(0-∞) was decreased on days rifampin was administered, for both R-warfarin (25% reduction; P < 0.001) and S-warfarin (15% reduction; P < 0.05). No differences were seen in the area under the international normalized ratio (INR)-time curve. Our study suggests that hepatic uptake via OATPs may not be clinically important in the pharmacokinetics of warfarin.