INTERACTION BETWEEN TERBINAFINE AND WARFARIN

A 71-year-old woman presented with gastrointestinal bleeding. She had been stabilized on warfarin for the previous few months. Terbinafine h ad been started 32 days prior to this episode for the treatment of ony chomycosis. The patient had been on cimetidine for the previous 2 year s and on other medications for the last 10 years. At the time of admis sion for the gastrointestinal bleeding, the coagulation indices were a ll above the therapeutic range. Endoscopy of the gastrointestinal trac t exhibited diffuse intestinal 'oozing' consistent with coagulopathy a s the cause of bleeding. Terbinafine may have had an effect on the met abolism of warfarin since both are metabolized through the liver and c imetidine can reduce terbinafine clearance by 33% resulting in higher concentrations of the antifungal agent. Our experience suggests that c aution should be exercised when prescribing terbinafine to a patient r eceiving warfarin.