Pfizer is keeping faith in tafamidis despite receiving a complete response letter from the US Food and Drug Administration for its transthyretin familial amyloid polyneuropathy drug.

The agency has turned down the New York-based giant's New Drug Application for tafamidis meglumine for TTR-FAP, a progressive and fatal neurodegenerative disease that affects some 8,000 patients worldwide (including about 3,000 Americans). It was developed by Pfizer subsidiary FoldRx.

Specifically the FDA is requesting the completion of a second efficacy study "to establish substantial evidence of effectiveness prior to an approval". It has also asked for additional information on the data within the current tafamidis NDA.

Last month, the FDA's Peripheral and Central Nervous System Drugs Advisory Committee met to discuss the clinical data package for tafamidis. Panellists were not asked on whether to recommend approval of the drug, but the committee did vote 13-4 that the data did not show "substantial evidence of efficacy on a clinical endpoint". However, the panel also voted 13-4 that the data "provide substantial evidence of efficacy for a surrogate endpoint that is reasonably likely to predict a clinical benefit".

Yvonne Greenstreet, head of the medicines development group for Pfizer’s specialty care business unit, noted that “TTR-FAP is a relentless and debilitating disease [and] we understand the urgent need within the patient community and stand firmly behind this innovative medicine". She added that  “it is our intention to request a meeting as soon as possible with the agency in order to discuss a potential path forward".

Tafamidis, which has been granted orphan drug status and a priority review, was approved by the European Commission last November, with the brand name Vyndaqel.