Between January 1 and June 30, 2007, FDA received 85 post-marketing reports in which patients who switched from Wellbutrin XL 300 mg to Teva?s bupropion formulation (Budeprion XL 300 mg) experienced an undesirable effect. Specifically, in 78 of these cases, there was a reported loss of antidepressant effect following a switch from the branded to generic product.  In addition to the loss of effect, a number of cases also reported the new onset or worsening of side effects.  The reported side effects were consistent with the adverse effects in labeling for bupropion products.  More than half of the patients who switched back to Wellbutrin XL 300 mg reported improvement of depression and/or abatement of side effects.

To evaluate this series of post-marketing reports, FDA hyas re-examined both the data on the bioequivalence of the two products (Wellbutrin XL and Teva's bupropion XL) and what is known about the natural history of treated depression. 

The conclusion of the FDA is that it considers the generic form of bupropion XL 300 mg (Teva Pharmaceuticals) bioequivalent and therapeutically equivalent to (interchangeable with) Wellbutrin XL 300 mg. Although there are small differences in the pharmacokinetic profiles of these two formulations, they are not outside the established boundaries for equivalence nor are they different from other bupropion products known to be effective. The recurrent nature of MDD offers a scientifically reasonable explanation for the reports of lack of efficacy following a switch to a generic product.  The adverse effects (e.g., headache, GI disorder, fatigue and anxiety) reported following a switch were relatively few in number and typical of adverse drug events reported in drug and placebo groups in most clinical trials (i.e., including, but not specifically for, bupropion).  Although many of these adverse effects are seen soon after drug therapy is initiated, adverse effects are known to occur throughout the course of a patient?s therapy, as well as among patients on a stable dose of medicine or in patients receiving placebo.  FDA continues to closely monitor reports of adverse events and therapeutic inequivalence.

The FDA report is available at: http://www.fda.gov/cder/drug/infopage/bupropion/TE_review.htm