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Comparative bioavailability of a generic phenytoin and Dilantin
D H Rosenbaum1, A J Rowan, L Tuchman
1Neurology Service, VA Medical Center, Bronx, New York.
Epilepsia
|May 1, 1994
Summary
Generic antiepileptic drugs (AEDs) may show lower serum levels, impacting patient treatment. This study found phenytoin levels were 22-31% lower with a generic formulation, highlighting potential biologic inequivalence.
Area of Science:
- Pharmacology
- Clinical Pharmacy
- Drug Safety
Background:
- Generic substitution of antiepileptic drugs (AEDs) is debated due to concerns about biologic and therapeutic inequivalence.
- Alleged instances of inequivalence have been reported, creating controversy in clinical practice.
Purpose of the Study:
- To systematically evaluate the biologic equivalence of a generic phenytoin (PHT) formulation.
- To assess potential therapeutic inequivalence in patients within the Veterans Administration (VA) system.
Main Methods:
- A retrospective analysis of serum PHT levels in patients at the Bronx VA Medical Center.
- Comparison of PHT levels during intake of a specific generic formulation versus the brand-name drug, Dilantin.
Main Results:
- Serum PHT levels were 22-31% lower when patients received the generic formulation compared to Dilantin.
- Literature review identified only one other documented case of potential clinically significant inequivalence between branded and generic AEDs.
Conclusions:
- While apparent generic AED inequivalence is infrequent, this study demonstrates a case of biologic inequivalence with a generic PHT formulation.
- Improvements are needed in the procedures for certifying the therapeutic equivalence of generic drugs.