RIFAMPICIN (RIFAMPIN) AND WARFARIN AND OTHER ORAL ANTICOAGULANTS

The anticoagulant effects of acenocoumarol, phenprocoumon and warfarin are markedly reduced by rifampicin.
A marked reduction occurs within 5 to 7 days of starting rifampicin, persisting for up to 5 weeks after the rifampicin is stopped. Monitor the INR closely. The warfarin dosage may need to be at least doubled.