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FDA worries about safety of Onyx's carfilzomib

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Ahead of a key advisory committee meeting this week, the FDA posted a staff assessment about the merits of greenlighting Onyx Pharmaceuticals' ($ONXX) closely watched cancer drug carfilzomib for multiple myeloma. And the remarks harp on the experimental drug's safety risks, which promise to be a big topic of discussion when agency advisers on Wednesday take up the company's application for approval.

Agency staff has reservations about the potential dangers of the South San Francisco-based biotech's injected proteasome inhibitor. "FDA is very concerned with the severe toxicities, including deaths that are associated with the use of this agent," the staffed noted. "The pathogenesis of these toxicities is not understood. Considering these factors, the risks of carfilzomib may not outweigh its benefits."

Onyx is seeking approval based in large part on findings from a single-arm, mid-stage study, which is a key parcel in the data package that the agency already deemed too thin for expedited review of the approval app. In the briefing documents released today, the FDA notes that 22% of patients in the key trial responded to the drug, which might not provide an advantage over existing treatments for the blood cancer. With those efficacy results came a list of safety concerns, including "life-threatening" heart toxicities that were linked to safety issues that included deaths and early study dropouts. They also said that pulmonary problems and liver toxicity were found in patients treated with the drug.

The FDA is expected to weigh the advisory committee's advice in deciding the fate of carfilzomib by July 27, and the agency's decision could impact rumored discussions about a buyout of Onyx. The company already provides the big-selling cancer drug Nexavar with collaborator Bayer Healthcare, which has been one of the names to surface in talks among bankers about the sale of Onyx. Any buyer will have to assess the likelihood of carfilzomib's approval in evaluating Onyx, or hold out for the FDA's word on the NDA later this summer. Obviously, Onyx has a lot riding on the future of the drug, which it took over in its 2009 buyout of Proteolix for $851 million.

And as with any new cancer drug, pharma manufacturers have to consider the market and reimbursement for the new treatments after regulatory decisions. There are already 7 FDA-approved drugs for multiple myeloma, including Takeda/Millennium's Velcade and Celgene's ($CELG) Revlimid, according to the FDA briefing documents.

- see Reuters' article
- and Businessweek's report

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