Bioavailability of warfarin in a patient with severe short bowel syndrome.

Acquired warfarin resistance has resulted from altered drug metabolism and excessive vitamin K. A third possible mechanism, decreased gastrointestinal absorption of the drug, was examined in a patient with short bowel syndrome and severe malabsorption who demonstrated transient warfarin resistance. Despite the resistance, bioavailability studies demonstrated normal drug absorption and a prolonged half-life. The parenteral administration of vitamin K proved to be the cause of the prolonged warfarin resistance.