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