Cotrimoxazole是sulfamethoxazole和trimethoprim兩種抗菌成分複方組成之抗生素，其常見的副作用包括皮膚過敏反應、噁心、嘔吐和肝腎毒性等，在血液方面亦曾有引起溶血性貧血的副作用報告。本文報告一位59歲女性，在接受腦部腫瘤切除手術後於住院期間因併發泌尿道感染，給予口服cotrimoxazole治療後並改由門診繼續追蹤治療。然而病患因全身虛弱、噁心、食慾不佳和尿液呈現茶褐色，經身體評估檢查發現結膜蒼白和黃疸性鞏膜，血液檢查值紅血球數1.57 106/L、血色素4.5 g/dL和血球容積比13.9%，在排除其它可能引起相同副作用之原因後，被診斷為cotrimoxazole引起的溶血性貧血。在停用cotrimoxazole後，病患紅血球數、血色素和血球容積比逐漸恢復至正常值。因此藉由此病例報告來探討cotrimoxazole引起溶血性貧血之可能機轉與處理方式。

Cotrimoxazole is an antibacterial agent that is a combination of sulfamethoxazole and trimethoprim. The most common adverse reactions of cotrimoxazole includes dermatologic reaction, nausea, vomiting and hepatotoxicity, etc. Cotrimoxazole has been associated with hemolytic anemia in a few case reports. We report a 59-year-old woman acceptted parietal craniotomy and removal of meningioma, and was complicated with urinary tract infection.  She received cotrimoxazole during the admission, and followed up in our out patient department. She developed general weakness, nausea, poor appetite and tea-color urine. Physical examination revealed pale conjunctiva and icteric sclera. The red blood cell counts 1.57 million/cmm, hemoglobin 4.5 g/dL and hematocrit 13.9%. Hemolytic anemia caused by cotrimoxazole was diagnosed after rule out any other problem that can cause the same side effects. When cotrimoxazole was discontinued , her red blood cells, hemoglobin and hematocrit were recovered gradually. We discuss the possible mechanisms and management of cotrimoxazole-induced hemolytic anemia.