Comparative bioavailability of a generic phenytoin and Dilantin

Generic substitution of antiepileptic drugs (AEDs) has been controversial, with many alleged instances of biologic and therapeutic inequivalence reported. The recall of a generic phenytoin (PHT) formulation used in the Veterans Administration (VA) medical system allowed us to evaluate the question of biologic equivalence systematically in a relatively large number of patients at the Bronx VA Medical Center. Serum PHT levels were 22-31% lower during the period of generic intake as compared with levels in the same patients receiving Dilantin. Review of the literature showed only one other adequately documented report of potential clinically significant inequivalence between a brand name and generic AED. Despite the apparent infrequency of generic inequivalence, several areas in which procedures for certification of therapeutic equivalence should be improved were identified.