Phenytoin, formerly known as diphenylhydantoin, is a potent anticonvulsant used to treat and prevent generalized grand mal seizures, complex partial seizures and status epilepticus. Phenytoin was formerly the most commonly used anticonvulsant agent but is now declining in use, having been replaced by more modern, better tolerated agents. Phenytoin is an uncommon but well known cause of acute idiosyncratic drug induced liver disease that can be severe and even fatal.