Five days after starting warfarin therapy in a patient of atrial fibrillation the 60 year old man returns to his physician complaining of large patches of discolored stain over his gluteal region and legs. This complication is most likely the result of:
a. Antithrombin III deficiency
b. Protein C deficiency
c. Drug allergy
d. Very high INR
The large patches of discolored stain over the gluteal region and legs five days after starting warfarin therapy are most likely the result of **Protein C deficiency**. This is due to warfarin-induced skin necrosis, which occurs because Protein C, a natural anticoagulant, has a shorter half-life than the clotting factors it affects. When warfarin is started, Protein C levels drop quickly, potentially leading to a hypercoagulable state and skin necrosis. This condition is not directly related to antithrombin III deficiency, drug allergy, or an excessively high INR in this context.