The generic versions of brand name drugs are only approved for use if they are chemically identical to the brand name drug. But a generic of Wellbutrin differs too much.
The U.S. Food and Drug Administration announced October 3 that budeprion XL 300 mg extended release tablets are not therapeutically equivalent to Wellbutrin XL 300mg.
This means the 300 mg version of the budeprion does not work in an identical manner as the 300 mg pill of Wellbutrin XL, and it may not be as effective.
The FDA changed the generic drug's rating from "AB" to "BX," which means the budeprion fails to match the Wellbutrin. The change only applies to the 300 mg tablets, not the 150 mg tablets.
Budeprion is marketed by Teva Pharmaceuticals USA, Inc. and manufactured by Impax Laboratories, Inc., who have asked the FDA to withdraw its approval of the 300 mg extended release version of the medication.
The budeprion 300 mg was approved by the FDA in December 2006 based on studies showing that the 150 mg budeprion was clinically and biologically equivalent to the 150 mg Wellbutrin.
Four other generic versions of Wellbutrin 300 mg were also approved.
After these drugs appeared on the market, patients who began using the generics reported lower effectiveness of the medication to the FDA.
The FDA investigated the reports and determined that the budeprion manufactured by Impax/Teva was the generic involved in these complaints.
The FDA then requested that Impax/Teva study the effectiveness of the 300 mg tabs directly, including in the study some of those who made the complaints.
Impax/Teva attempted to conduct this study but wasn't able to find enough participants so that they had enough good data, so they ended their attempts in late 2011.
Therefore the FDA conducted its own small study comparing the Wellbutrin XL 300 mg with the budeprion XL 300 mg in 24 healthy adult volunteers.
The FDA's results, released in August 2012, found that the budeprion tablets did not release the active ingredient, bupropion, into the participants' blood as well as the Wellbutrin.
The rate of the release and the amount of the release was different between the generic and the brand name drug.
Because the budeprion may not be as effective or helpful to patients, it downgraded the product's "bioequivalence" rating.
The other four generic versions, manufactured by Anchen, Actavis, Watson and Mylan, were not tested by the FDA, but the organization has asked those companies to test their 300 mg XL bupropion tablets as well to see if it's equivalent to the Wellbutrin one.
The data from these studies is due by March 2013.
Meanwhile, Impax/Teva have stopped shipping the 300 mg XL budeprion.
"Patients taking Budeprion XL 300 mg as a substitute for Wellbutrin XL 300 mg should talk with their health care professionals if they have questions about taking this medication," the FDA recommended.