5-Fluorouracil(5-FU)是屬於抗代謝作用的抗腫瘤藥品，一般用於治療各種實體的腫瘤(solid tumor)，如大腸癌、直腸癌、乳癌、胃癌、胰臟癌、肝癌、頭頸部癌及膀胱癌等。其常見的副作用有骨髓抑制和腸胃道方面症狀，如噁心、嘔吐、腹瀉、食慾缺乏(anorexia)。禿髮、皮膚炎和心臟毒性也是會發生的副作用，而神經毒性(neurotoxicity)則很少被報告。本案例為一位58歲男性，下咽惡性腫瘤(hypopharyngeal cancer)患者，在接受化療藥品Etoposide、Carboplatin和5-FU投予完成後，病人出現躁動不安，在床上反覆坐起躺下，意識改變等中樞神經方面異常症狀。Glasgow昏迷指數(GCS)：E3M4Vt，瞳孔大小：右眼(R’t)/左眼(L’t) 4.5mm/4.5mm且對光照有反應。血液檢查發現氨(Ammonia) 488 mg/dL，血液尿素氮(Blood Urea Nitrogen)25mg/dL，肌胺酸酐(Creatinine)2mg/dL。在排除其他可能引起相同副作用之原因後，診斷為疑似5-FU藥物引起的代謝性腦病變。經給予靜脈點滴輸注液補充和支持性照顧下，病人情況逐漸恢復正常後出院。本病例報告主要探討5-FU引起腦病變之可能的作用機轉與處理方式。

5-Fluorouracil (5-FU), a fluorinated pyrimidine, is an antineoplastic antimetabolite. It is used in the treatment of a variety of solid tumors, such as carcinoma of the colon, rectum, breast, stomach, pancreas, liver, head and neck, and bladder. Common adverse effects of 5-FU are related to its effects on the bone marrow (leukopenia) and gastrointestinal epithelium (nausea, vomiting, diarrhea, anorexia). Other adverse effects are alopecia, dermatitis, and cardiotoxicity. 5-FU-induced neurotoxicity is uncommon. A 58-year-old male was diagnosed as having hypopharyngeal squamous cell carcinoma with multiple lung and bone metastases and cervical lymphadenopathy. He was admitted for scheduled chemotherapy with Etoposide+ Carboplatin + 5-FU. After the infusion of chemotherapy, the mental status changed with Glasgow Coma Scale (GCS): E3M4Vt. The pupil size of both sides were 4.5mm and both pupils reflected to light. The patient stood up and laid down repeatedly. Ammonia level wa s 433µg/dL, blood urea nitrogen 25 mg/dL and serum creatinine 2 mg/dL. Excluding other medications and diseases, it is probable that encephalopathy was caused by 5-FU. After giving intravenous fluid supplement and supportive care, the patient gradually recovered and was finally discharged. The possible mechanisms and management of 5-FU-induced encephalopathy are discussed.