A potential interaction between warfarin and atovaquone.

Objective: To report a case of increased international normalized ratio (INR) in a patient established on warfarin therapy who was then initiated on atovaquone therapy.

Case Summary: A 53-year-old African American male with HIV was prescribed warfarin 5 mg/day for 12 months after diagnosis of idiopathic deep vein thrombosis and bilateral pulmonary emboli (target INR 2.5 [range 2.