Mephenytoin⋆ [Methoin; Methylphenylethylhydantoin; Phenantoin]

Mephenytoin pharmacotherapy usually is prescribed in combination with other anticonvulsant pharmacotherapy, particularly phenytoin pharmacotherapy. Mephenytoin has an onset of action of 30 minutes and a duration of action of 24 to 48 hours following oral ingestion. Mephenytoin is metabolized in the liver to its principal active and toxic metabolite, 5,5-ethylphenylhydantoin. Mephenytoin pharmacotherapy has been associated with serious and potentially fatal blood disorders. Mephenytoin pharmacotherapy commonly has been associated with drowsiness, which is generally dose related. Signs and symptoms of mephenytoin overdosage are similar to the signs and symptoms associated with phenytoin overdosage (see the phenytoin monograph). Mephenytoin overdosage requires emergency symptomatic medical support of body systems with attention to increasing mephenytoin elimination.