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Epilepsy Medications: When Is It Safe to Substitute a Generic?

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Potential Problems With Generic Epilepsy Drugs

There may be several ways switching to generic epilepsy drugs could cause potential problems, experts say. Many epilepsy drugs are absorbed and metabolized in more complex ways than other drugs. Researchers argue that although the differences in generics allowed by the FDA do not affect treatment for most conditions, the differences could have a negative impact for treating epilepsy.

For instance, in one study, volunteers took brand-name Dilantin or the generic version of Dilantin, which is phenytoin. Those taking generic phenytoin had average drug levels that were 13% lower over time than in those taking brand-name Dilantin. Computer simulations predicted that over time, half of those taking generic phenytoin would have blood levels too low to prevent seizures.

To be sure of their equivalence with brand names, generic drugs are tested only in healthy adults. In real life, people taking epilepsy drugs often have multiple medical problems and take other medications, which could lead to differences:

  • The FDA acknowledges that because a large number of manufacturers make generic drugs, the chance exists that a limited number of epilepsy drugs not truly equivalent to brand-names could reach the market. 
  • Generics aren't tested against each other; each is tested only against the brand name. "One could be slightly lower than the brand, and another slightly higher," says French. "They both meet quality standards, but they could be significantly different from each other."

The variance between generic drugs is a likely cause of any problem that exists, according to French. She believes the biggest problem lies not in the initial switch, but in repeated switching between generic epilepsy drugs made by different manufacturers.

Because generic drugs are often made by multiple manufacturers, says French, "some people are being switched from generic to generic every month. Even if there's a small variation between each generic form, you have no idea what's happening with the person's blood levels."

She's even seen a patient who had a bottle of generic pills with half from one manufacturer and the other half from another manufacturer, when the pharmacy changed suppliers after running out while filling the prescription.

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