FDA rescinds Merck HCV therapy's Breakthrough Designation

And then there were two. In an unprecedented move, Merck announced in its fourth-quarter and full-year earnings call Wednesday that the FDA has rescinded Breakthrough Therapy designation for HCV combo drug grazoprevir/elbasvir. The determination was based on the availability of existing drugs that already address that medical need.

The FDA's decision could delay Merck's doublet HCV therapy launch from early to mid-2016. Without Breakthrough Therapy designation, Merck's submission must adhere to standard NDA (new drug application) timelines, leaving the FDA with 10 months to evaluate the drug rather than six. During the call, Roger Perlmutter, president of Merck Research Laboratories, said that the company plans to discuss this matter with the agency in the coming weeks.

Merck spokesperson Lanie Keller told MM&M that the drug's profile, as well as the commencement of Phase-III studies, still support a filing in the first half of 2015. “We continue to believe that Phase-II data presented at AASLD last November demonstrating the potential of our doublet therapy to provide sustained virologic responses in the majority of infected patients, irrespective of comorbidities, coupled with the full enrollment of our Phase-III studies, should permit FDA filing in the first half of 2015,”  she explained.

That potential delay leaves Gilead's HCV cures Sovaldi and Harvoni, as well as AbbVie's recently approved Viekira Pak, with more time to gain market share, influence and brand recognition. Gilead reported fourth-quarter 2014 US sales of $1.2 billion for Sovaldi and $2 billion for Harvoni. AbbVie's chief executive Richard Gonzalez told analysts last week that he believes Viekira Pak could reach yearly sales of $3 billion by the end of 2015.

Merck doubled down on its HCV efforts this past August when it spent $3.9 billion on a nucleotide, IDX21437, now known as MK-3682. In Wednesday's call, Merck stated that the company has begun Phase-II testing of Idenix's nucleotide with grazoprevir (MK-5172) and elbasvir (MK-8408). Merck expects to start Phase-III testing of its triplet combination therapy by the end of 2015.

Perlmutter told Forbes's Matthew Herper around the time of the Idenix acquisition that although Merck's product would not be first to market, there are 170 million HCV sufferers in the world. Furthermore, Perlmutter said that he believed that number was unlikely to dwindle in just a few years, leaving Merck's combination therapy with a sufficient patient population to treat when it debuts.