Phenytoin [Diphenylhydantoin]

Abrupt discontinuation of phenytoin pharmacotherapy among patients who have seizure disorders may result in withdrawal seizures and status epilepticus. The exact mechanism of action of phenytoin for the prophylactic and symptomatic management of seizure disorders has not yet been fully determined. However, a major component of phenytoin’s anticonvulsant action appears to be related to the reduction of post-tetanic potentiation of synaptic transmission and associated limitation of seizure discharge and spread from its focus within the motor cortex. Phenytoin pharmacotherapy has been commonly associated with decreased coordination, mental confusion, and slurred speech. Signs and symptoms of phenytoin overdosage also include circulatory depression, coma, hyperflexia, hypotension, lethargy, nausea, respiratory depression, slurred speech, and vomiting. Phenytoin overdosage is potentially fatal and should be treated as a medical emergency requiring symptomatic medical support of body systems with attention to increasing phenytoin elimination. Phenytoin also reduces the maximal activity of the brainstem centers that are responsible for the tonic phase of tonic-clonic seizures.