sion and pain upon palpitation over the lower abdominal area, and a large ecchymosis was noted over the left flank. Laboratory tests revealed hemoglobin of 4.9 mg/dL and PT of 56.2 seconds with an INR of 5.1. Computed tomography of the abdomen showed hemoperitoneum and left abdominal wall hematoma ( Figure 1). Because the diagnostic hypothesis was warfarin-induced hemoperitoneum and hematoma, she received component therapy with fresh frozen plasma and parenteral vitamin K for correction of bleeding. Her condition gradually improved, and she was discharged uneventfully 3 weeks later.This woman had received oral anticoagulant therapy for prevention of a thromboembolic event, and INR was maintained at approximately 2.5, but prolonged PT and a high INR with severe bleeding developed during hospitalization for pneumonia. The possible mechanism of unexpectedly high INR was the interaction between moxifloxacin and warfarin. Previous studies have demonstrated this rare clinical effect of the interaction between moxifloxacin and warfarin. 3,4 In contrast to previous reports that gastrointestinal bleeding was the most common complication, 3 the presentation of hemoperitoneum and abdominal wall hematoma found in the present case was rarely reported.Although moxifloxacin rarely interacts with warfarin, physicians should consider the potential drug interaction between moxifloxacin and warfarin in this era of their increasing use. 2,5,6 Monitoring of INR for individuals taking warfarin during use of moxifloxacin is needed to detect possible adverse effects and prevent further bleeding complications.
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