Inability to attain oral anticoagulation: warfarin-rifampin interaction revisited.

The warfarin-rifampin interaction is a well-described but underappreciated drug interaction. A case is reported in which therapeutic anticoagulation could not be achieved after nearly 4 weeks of warfarin therapy because of simultaneous administration of rifampin. This patient had the highest warfarin clearance ever reported in the literature. The world's literature describing warfarin-rifampin interactions for the past 32 years was reviewed to suggest guidelines for warfarin dosage when rifampin is given simultaneously.