Mephenytoin is N-methylated at position 3 with an ethyl group replacing one of the phenyl substituents at position 5.
It is indicated for focal and jacksonian seizures in patients refractory to less toxic AEDs. Mephenytoin produces more sedation
than phenytoin and should be used only when safer drugs have failed, because it is associated with an increased incidence of
serious toxicities, such as severe rash, agranulocytosis, and hepatitis. Its N-desmethyl metabolite, 5-phenyl-
5-ethylhydantoin, contributes to both efficacy and toxicity for mephenytoin. The drug is no longer commercially available inside
but is still available outside the United States.
