FDA panel mixed on Pfizer's rare disease drug

Pfizer's pioneering rare-disease drug tafamidis garnered mixed reviews from FDA advisers Thursday, casting further uncertainty over whether the agency will green-light the treatment for the U.S. market. Both the agency's advisers and staff have harped on the lack of efficacy data for the oral drug in patients with transthyretin familial amyloid polyneuropathy, a rare and fatal neurodegenerative disease.

As Reuters reports, the advisory committee voted 13-4 that Pfizer's ($PFE) drug failed to hit the main goal of a study. Yet advisers endorsed evidence, in a 13-4 vote, of a separate efficacy endpoint that could indicate that the drug provides a clinical benefit for patients with the disease. The panel did not vote on whether the benefits of the drug warranted approval, after FDA staff gave the application a thumbs down earlier this week.

Aiming to build its burgeoning rare-disease business, Pfizer made a risky bet with its application for U.S. approval of tafamidis because the data package relied on evidence from a single study. FDA staff slammed the "inadequate evidence of effectiveness" and backed a plan to send the U.S. drug giant packing with a Complete Response Letter for the application, forcing Pfizer to build a bigger case for the drug before returning to the agency for a market nod.

Pfizer's argument for approval relies in part on the fact that there are no FDA approved treatments for the rare disorder, which affects an estimated 8,000 patients worldwide and roughly 2,500 people in the U.S. Regulators have allowed such treatments for small groups of patients to sail to approvals based on slim packages of clinical trials data, as European regulators did last year for Pfizer's tafamidis. We'll see whether the FDA follows suit.

- here's Pfizer's release
- check out Reuters' report