FDA panelists chide Merck, but ultimately back approval of C. diff drug


Merck ($MRK) has emerged from an FDA expert panel meeting with a recommendation for approval of a monoclonal antibody designed to prevent the recurrence of Clostridium difficile infections. But the Big Pharma took some blows on the way to a 10-5 vote in its favor, with panelists criticizing it for the size of the Phase III program and other perceived shortcomings.

The drug, fully human monoclonal IgG1/kappa antibody bezlotoxumab, binds to and neutralizes C. difficile toxin B, a mechanism of action intended to prevent effects on the gut wall that can lead to abdominal pain and diarrhea. Merck tested the antibody, which it licensed from Medarex months before the biotech’s takeover by Bristol-Myers Squibb ($BMY), in a two-trial Phase III program. The Phase III program met its primary endpoint of reduction in C. difficile recurrence as compared to placebo, but the data failed to satisfy all of the experts tasked with assessing the filing for the FDA.

Merck thinks the drug could prevent almost 50,000 infections with C. difficile a year. Given the size of the population addressed by bezlotoxumab, some of the panelists, including Antimicrobial Drugs Advisory Committee Chair Lindsey Baden, felt Merck should have tested it on more people. "This is not a rare disease," Baden said, according to BioWorld. Generating data in more subjects could have enabled Merck to answer questions the panel had about which patients are likely to respond best to bezlotoxumab, which Merck plans to market under the brand name Zinplava.


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As it was, 5 of the panelists recommended against approving the product on the basis of the data available, while another panelist abstained. Many of the experts voting "no" still see a path forward for bezlotoxumab, while some of those in favor of approval have reservations about its use. The mixed response follows on from doubts raised by the FDA’s own staff about the efficacy of the drug. The FDA took issue with the endpoint used in the trials, although Merck’s reasoning for the decision placated enough of the panel to secure their backing. The final decision now rests with the FDA.

Whichever way the FDA leans, Merck and the rest of the world won’t have to wait too long to find out. Bezlotoxumab has priority review status and, as such, the FDA is expected to make a decision by July 23. A positive decision would represent a small boost for Merck. As of late last year, the Thomson Reuters Cortellis database put the consensus forecast for 2020 global sales at $350 million.

- read the release
- here’s BioWorld’s take
- and Medscape’s coverage (reg. req.)

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Merck lines up for a quick approval with its C. diff therapy
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