Phenytoin為抗癲癇藥，其適應症為大發作性癲癇、複雜型部分性（精神運動性）癲癇、預防及治療神經外科手術時所引起的癲癇發作、重積性癲癇及抗心律不整。該藥物常見之副作用有眩暈、便秘、噁心、運動失調（ataxia）、神智混亂、異常興奮、眼球震顫、無力、齒齦增生、皮疹等。而血液惡液質（blood dyscrasias）、淋巴瘤、多毛症、肝炎、紅斑性狼瘡樣的症狀、史蒂芬－詹森併發症則是較為罕見的副作用。
本文報告一位48歲女性病患，因蜘蛛膜下腔出血，使用phenytoin作為預防及治療神經外科手術時所引起的癲癇發作。在投予此藥21天後出現顆粒性白血球缺乏症（agranulocytosis），此情形是鮮少發生的副作用。故藉由此病例來探討其可能機轉及處置方法。
 

Phenytoin is an antiepileptic drug indicated for generalized tonic-clonic seizures, complex partial seizures (psychomotor), seizures in neurosurgery (prophylaxis and treatment), status epilepticus and arrhythmias.  The common side effects of phenytoin are dizziness, constipation, nausea, vomiting, ataxia, confusion, unusual excitement, nystagmus, lethargy, gingival hyperplasia and skin rash etc.  Rare side effects of phenytoin include blood dyscrasias, lymphoma, hypertrichosis, hepatitis, SLE-like syndrome, Stevens-Johnson syndrome.  
We report a clinical case of a 48-year-old woman with subarachnoid hemorrhage who received phenytoin for the prevention and treatment of seizures in neurosurgery. The patient developed agranulocytosis—a rare adverse reaction associated with phenytoin—after taking phenytoin for 21 days. We discuss the possible mechanism, and the management, of phenytoin-induced agranulocytosis.