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NEUROLOGY 2008;71:525-530
© 2008 American Academy of Neurology

Generic substitution in the treatment of epilepsy

Case evidence of breakthrough seizures

M. J. Berg, MD, R. A. Gross, MD, PhD, K. J. Tomaszewski, PhD, MS, W. M. Zingaro and L. S. Haskins, MPA

From the Strong Epilepsy Center, Department of Neurology (M.J.B., R.A.G.), Department of Pharmacology and Physiology (R.A.G.), and Department of Community and Preventive Medicine (K.J.T.), University of Rochester Medical Center; KJT Group (K.J.T.), LLC, Honeoye Falls; and Harris Interactive, Inc. (W.M.Z., L.S.H.), Health Care Research Division, Rochester, NY.

Address correspondence and reprint requests to Dr. Michel J. Berg, Strong Epilepsy Center, University of Rochester Medical Center, 601 Elmwood Ave. Box 673, Rochester, NY 14642-8673 Michel_Berg{at}URMC.Rochester.edu

Objective: There are concerns that generic and brand antiepileptic drugs (AEDs) may not be therapeutically equivalent. This study investigated how generic AED substitution may have negative consequences.

Methods: Sixty-nine of 150 physicians who participated in a large survey on generic AED substitution completed a case review form regarding a patient who experienced a loss of seizure control due to a generic AED. Nineteen were excluded from analysis.

Results: Fifty patients, well-controlled on a brand AED, subsequently experienced a breakthrough seizure or increased seizure frequency after switching to a generic without other provoking factors. AEDs included phenytoin (15 cases), valproic acid (14), carbamazepine (7), gabapentin (8), and zonisamide (8). Two patients were on a combination of two AEDs, both of which were switched to generics. In 26 cases serum AED levels were known both before and after generic substitution. Twenty-one had lower levels at the time of the breakthrough seizure on the generic medication. Loss of seizure control had a negative impact on quality of life, including loss of driving privileges (n = 30) and missed school/work days (n = 9).

Conclusions: Changing from a brand antiepileptic drug (AED) to a generic may result in seizures. This raises the concern that current Food and Drug therapeutic equivalence testing regulations may not be adequate for AEDs and suggests that more clinical evidence is needed. Physicians, pharmacists, patients, and policy makers should be aware that for some patients there may be risks associated with switching from brand to generic AEDs.

Abbreviations: AED = antiepileptic drug; FDA = Food and Drug Administration.

Supplemental data at www.neurology.org

Disclosure: Research supported by GlaxoSmithKline, Research Triangle Park, NC.

Received August 3, 2007. Accepted in final form May 5, 2008.






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