Generic antiepileptic drugs

Opinion statement

Generic antiepileptic drugs (AEDs) generally provide safe, effective, lower-cost alternatives to brand-name drugs. To be approved by the US Food and Drug Administration (FDA), manufacturers must show that generic drugs are comparable to brand-name formulations, meeting bioequivalence, dissolution, and manufacturing quality standards. Bioequivalence for most generic formulations is evaluated by measuring blood pharmacokinetic values in a small, crossover study of adult volunteers taking single doses of brand-name and generic AEDs. Bioequivalence standards require that ratios of average peak drug concentrations (C_max) and total extent of absorption (area under the curve, AUC) for a test drug be within 80% to 125% of the reference brand-name drug, with a confidence interval of 90%. Bioequivalence of most generic AEDs, however, has not been evaluated in patients with epilepsy or in other special populations such as elderly patients or patients taking multiple AEDs and prodrugs. Moreover, evidence is limited regarding the adequacy of FDA generic standards for AEDs, particularly for “narrow therapeutic ratio” medications such as oxcarbazepine, although two carbamazepine studies are supportive. Most patients can successfully initiate therapy with generic AEDs and can safely switch from brand-name to generic AEDs (and sometimes back again). The FDA, however, has not shown safety in generic-to-generic switches, which could potentially cause drug concentration changes of up to 40%. Less expensive generic formulations will soon be available for most of the “second generation” AEDs—zonisamide, for example, recently had 17 generic formulations approved in the United States—providing substantial savings in health care costs.

In summary, although generic AEDs are generally safe and effective for most patients, the current bioequivalence standards may not be sufficient for certain patient populations and for certain drugs, requiring vulnerable patients to be monitored very carefully when converting to generic AEDs. The adequacy or inadequacy of FDA bioequivalence standards for AEDs has not yet been well evaluated with large, well-controlled studies.