RT Journal Article SR Electronic T1 Pharmacokinetic Interaction between Warfarin and a Uricosuric Agent, Bucolome: Application of In Vitro Approaches to Predicting In Vivo Reduction of (S)-Warfarin Clearance JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1179 OP 1186 VO 27 IS 10 A1 Takahashi, Harumi A1 Kashima, Toshitaka A1 Kimura, Sosuke A1 Murata, Noboru A1 Takaba, Toshihiro A1 Iwade, Kazunori A1 Abe, Tomio A1 Tainaka, Hitoshi A1 Yasumori, Toshio A1 Echizen, Hirotoshi YR 1999 UL http://dmd.aspetjournals.org/content/27/10/1179.abstract AB A uricosuric agent, bucolome, has been shown to intensify the anticoagulant effect of warfarin. The aims of the present study were to clarify its mechanism(s) and to apply in vitro approaches for predicting this potentially life-threatening in vivo interaction. An in vivo study revealed that Japanese patients given warfarin with bucolome (300 mg/day, n = 21) showed a 1.5-fold greater international normalized ratio than those given warfarin alone (n = 34) despite that the former received a 58% smaller warfarin dose than the latter. Enantioselective assays revealed that bucolome increased plasma unbound fractions of (S)- and (R)-warfarin by 2-fold (p < .01), reduced unbound oral clearances of (S)- and (R)-warfarin by 84 (p < .01) and 26% (p < .05), respectively, and inhibited the unbound formation clearance for (S)-warfarin 7-hydroxylation by 89% (p < .01). In contrast, bucolome elicited no appreciable changes in the plasma unbound (S)-warfarin concentration versus the international normalized ratio relationship. In vitro studies with recombinant human cytochrome P-450 2C9 and liver microsomes showed that bucolome was a potent mixed-type inhibitor for (S)-warfarin 7-hydroxylation, with Ki of 8.2 and 20.2 μM, respectively. An in vitro model incorporating maximum unbound bucolome concentration in the liver estimated as a sum of hepatic artery and portal vein concentrations and in vitroKi made an acceptable prediction for bucolome-induced reductions in in vivo total (bound + unbound) oral clearance, unbound oral clearance, and unbound formation clearance for (S)-warfarin. In conclusion, the augmented anticoagulant effect of warfarin by bucolome due to the metabolic inhibition for pharmacologically more potent (S)-warfarin may be predictable from in vitro data. The American Society for Pharmacology and Experimental Therapeutics