Cotrimoxazole是複方的抗微生物製劑，含有trimethoprim和sulfamethoxazole，由於治療成效佳及價格優勢，臨床上廣泛被應用於相關感染的治療，因此了解此藥品所引起的不良反應，也相當重要。高血鉀為 trimethoprim會造成電解質異常的不良反應之一，已有相當多的個案被報導和討論，提醒醫療人員，當患者有好發的危險因子時更應多加留意，密切監測。本個案報告，於使用cotrimoxazole 3天後，出現高血鉀，經過數天藥物治療但效果不佳，最終採血液透析和暫停藥品使用後才獲得改善。藉此案例提醒臨床醫療人員，使用此類藥品時需要提高警覺，小心監測臨床不尋常的徵兆，避免對患者造成嚴重的傷害。

Due to cost benefits and great effectiveness, cotrimoxazole contained with trimethoprim and sulfamethoxazole is one of popular antibiotics for some infection diseases control. It is essential to understand the adverse effects of cotrimoxazole. Hyperkalemia is one of electrolytes imbalance side effects. It has been reported and discussed extensively to remind care-givers the related risk factors to prevent unwanted situation happen. This case report was about cotrimoxazole-induced severe hyperkalemia after 3 days of cotrimoxazole therapy. It was in vain with medicine therapy to relief hyperkalemia. The adverse effect was remission under hemodialysis therapy and holding cotrimoxazol treatment finally. By this case report, we want to remind clinical care-givers to monitor closely and be more alertness about the adverse effects when administrating cotrimoxazole.