Biovail said that according to Teva, the trial is intended to address reports of inefficacy and adverse events by patients switching from Biovail's 300 mg Wellbutrin XL to Teva's generic version of the drug, Budeprion XL. Biovail said its knowledge of the proposed study came from a description by Teva published in a Dow Jones article of 2 December 2010. The article said 138 patients in the study would be confined in a clinical setting for 24 days.

According to FiercePharma, it is not often that we get data on patients switching from a branded medicine to a rival generic. But complaints about Teva's version of the antidepressant Wellbutrin XL drove FDA to study the matter. In 2007, the People's Pharmacy received multiple reports of increased side effects and decreased efficacy of generic bupropion, which prompted it to ask ConsumerLab.com to test the products in question. The tests showed that "one of a few generic versions of Wellbutrin XL 300 mg, sold as Budeprion XL 300 mg, did not perform the same as the brand-name pill in the lab". The FDA investigated these complaints and concluded that the Budeprion XL is equivalent to Wellbutrin XL in regard to bioavailability of bupropion and its main active metabolite hydroxybupropion. The FDA also noted that coincidental natural mood variation is the most likely explanation for the apparent worsening of depression after the switch from Wellbutrin XL to Budeprion XL.

The generics giant promised the agency it would run a head-to-head trial, pitting its version against the brand-name product. Teva has now proposed the parameters of that clinical trial, and Biovail - which makes the brand-name version - is objecting. Biovail claims that the trial's design - 138 patients and 24-day duration - would be inadequate for a true compare-and-contrast look at the two medications.

The trial's outcome could be big for Biovail, which bought out GlaxoSmithKline's US rights to Wellbutrin XL in 2009 for US$510 million. If Teva's version were proven to be somehow inferior to the brand-name product, then Biovail might reap millions in additional sales. At one time Biovail reaped US$2 billion a year from Wellbutrin XL, Reuters notes, but that was before generic competition ate into sales.

The trial - provided its design was considered sufficient by objective third parties - could end up being a big deal for brand-name and generics drugmakers alike. If a true, well-crafted, head-to-head trial found statistically significant differences between a branded product and a generic copycat, that could throw the whole generic-substitution thing way off whack and soften the blow of generic competition in a big way.

References:

Susan Taylor. UPDATE 1-Biovail says rival generic drug trial too small. Reuters. 2010 January 22.

Tracy Staton. Will generic Wellbutrin live up to brand? FiercePharma. 2010 January 25.

Jacqueline Stenson. Report questions generic antidepressant - ConsumerLab.com finds cheaper drug may not work the same as brand. MSNBC. 2007 October 12.

Review of Therapeutic Equivalence Generic Bupropion XL 300 mg and Wellbutrin XL 300 mg. FDA News Release. 2008 April 16.

FDA’S INVESTIGATION OF GENERIC ANTIDEPRESANT CALLED INADEQUATE BY CONSUMERLAB.COM AND THE PEOPLE’S PHARMACY. ConsumerLab News. 2008 April 16.