Extreme warfarin intoxication secondary to possible covert drug ingestion

A young adult male patient presented with an excessively prolonged prothrombin time (greater than 90 sec) following approximately two weeks of therapy with oral warfarin sodium, in doses between 2.5 and 5 mg/d. Repeated administration of vitamin K and fresh frozen plasma was required to reverse the anticoagulation and maintain a normalized prothrombin time. Serial warfarin plasma concentration measurements were used to interpret the apparently unusual prothrombin time response profile and to detect the possibility of covert drug ingestion.