Although generic versions of Topamax will soon be available, some neurologists are concerned the new formulations may endanger patients at high risk of seizure complications.
The Food and Drug Administration approved the marketing of generic topiramate for seizure disorders in April, and maintains that generic formulations of any drug must be bioequivalent to the brand formulation. But the agency's accepted bioequivalence range of 80%–125% could put some patients at risk for breakthrough seizures or increased side effects, Dr. Michael Privitera said.
“The FDA's bioequivalence requirements are not based on any strong evidence,” said Dr. Privitera, professor of neurology at the University of Cincinnati. “There are no studies that say people with epilepsy will do well within that range. The FDA could be correct in saying that generic formulations will fall within that range, but there is no way of knowing if that that range is good for our patients.”
Dr. Stuart Black, medical director of the Dallas Headache Association, agreed that the lack of evidence clouds the issue of which patients might experience problems if switched to a generic formulation. “We don't have any data at all on the similar comparison of using a generic antiepileptic for migraine as opposed to a nongeneric,” said Dr. Black, who is also the medical director of neurology and codirector of the Neuroscience Center at Baylor University Medical Center, Dallas.
The American Epilepsy Society recommends that generics should not be substituted for a brand formulation without physician and patient approval.