Bioequivalence Problem Results in Generic Antidepressant Withdrawal


One of the generic forms of the 300-mg dose of extended-release bupropion is being taken off the market because of evidence indicating that it is not therapeutically equivalent to the brand name version of the antidepressant, according to a Food and Drug Administration notice report posted on Oct. 3.

The affected product is Budeprion XL 300 mg, manufactured by Impax Laboratories and marketed by Teva Pharmaceuticals USA – one of the five generic versions of Wellbutrin XL 300-mg tablets that have been approved by the FDA. The planned withdrawal of the product is the result of studies conducted by the company and FDA aimed at addressing reports of reduced efficacy from patients who were switched to generic forms of Wellbutrin XL 300 mg made more than 5 years ago. These reports were made to the agency "soon after" the Impax/Teva product was approved in December 2006, and the FDA subsequently determined that the complaints "appeared to be linked to the Impax/Teva products," the statement said.

None of the other generic versions of the 300-mg dose or the Impax 150-mg bupropion product are affected, the FDA said.

However, the agency recently has requested that the four other manufacturers of generic versions of Wellbutrin XL 300 mg conduct bioequivalence studies of their products and to submit the results to the FDA by March 2013. (Those manufacturers are Anchen, Actavis, Watson, and Mylan).

Approval of all the generic versions of 300 mg extended-release bupropion was based on studies establishing that the 150-mg strengths were bioequivalent to the 150-mg dose of the brand-name product, according to the FDA guidance at that time. But the FDA "has determined that this approach is no longer appropriate" to establish bioequivalence and "is revising its guidance to industry for how to conduct premarket bioequivalence studies in generic bupropion products."

The bioequivalence problem was confirmed in an FDA-sponsored study conducted in 2010, comparing the bioequivalence of the Impax/Teva product to Wellbutrin XL 300 mg in 24 healthy adults, which determined that the generic tablets "fail to release bupropion into the blood at the same rate and to the same extent as Wellbutrin XL 300 mg," according to the statement. At the request of the FDA, Impax/Teva had started a study comparing the bioequivalence of the 300-mg product with the brand-name product, including patients who had reported the problem of reduced efficacy after the switch to the generic product. But the company was unable to recruit enough patients and terminated the study in late 2011.

Impax and Teva have stopped shipping this product.

Health care professionals and patients should report problems associated with drugs by visiting the FDA MedWatch program or calling 800-332-1088.

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