苯妥英（Phenytoin，或称diphenyl hydantoin），常见商品名大仑丁（Dilantin），是一种抗惊厥药物。该药在治疗强直－阵挛性发作及部份发作有治疗效果，但无法治疗失神性发作。苯妥英能借由口服或静脉注射给药，当癫痫重积状态发生时，可借由静脉注射给予苯妥英，相对的苯二氮䓬类则无法治疗该症状。该药也可治疗特定的心律不整及神经病变性疼痛。静脉注射给药通常会于30分钟内开始作用，药效可维持24小时，注射后可进行浓度监测以维持适当浓度。

常见副作用包含恶心、胃痛、缺乏食欲、肢体协调不良、毛发增长，以及牙龈增生。其他可能的严重副作用则包含嗜睡、自残、肝脏问题、骨髓抑制、低血压，以及毒性表皮溶解症。有证据显示妊娠期间服用该药物可能对胎儿造成不良影响，哺乳期间用药目前没有相关风险显示。服药期间并用乙醇可能干扰药效。

Phenytoin, sold under the brand name Dilantin among others, is an anti-seizure medication. It is useful for the prevention of tonic-clonic seizures, partial seizures, but not absence seizures. The intravenous form is used for status epilepticus that does not improve with benzodiazepines. It may also be used for certain heart arrhythmias or neuropathic pain. It can be taken intravenously or by mouth. The intravenous form generally begins working within 30 minutes and is effective for 24 hours. Blood levels can be measured to determine the proper dose.