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.