Dive Brief:

• The Food and Drug Administration has rejected Merck & Co’s experimental drug for chronic cough, issuing the company a complete response letter for a treatment it acquired via a 2016 buyout of drugmaker Afferent Pharmaceuticals.

• Merck last year submitted the drug, called gefapixant, to the FDA, which extended its review by three months before reaching a decision. According to Merck, the regulator raised questions in its letter related to gefapixant’s effectiveness, data for which was mixed in two late-stage clinical trials of the drug.

• In a Monday statement, the company said it would discuss next steps with the FDA and that it remains “committed” to advancing gefapixant. In Japan, meanwhile, Merck said regulators had last week approved gefapixant, which it will sell as Lyfnua there.

Dive Insight:

Merck executives have, as recently as last month, pegged gefapixant as an “important product” for the company, one that could have a “meaningful opportunity” on the market, if approved.

Others, however, haven’t been so sure, with one Wall Street analyst describing the Phase 3 study data supporting the drug as “marginal” at the time of its release. Those results showed a high dose of gefapixant significantly reduced coughing frequency in people with chronic cough that persisted despite treatment or was otherwise unexplained. But a lower dose didn’t, and people given a placebo in the trials also experienced less frequent coughing.

Merck said that while the FDA asked for more information on gefapixant’s efficacy, the agency’s letter did not relate to the drug’s safety. Complete response letters are not published publicly.

“We remain committed to advancing gefapixant for patients with refractory or unexplained chronic cough and will work with the FDA to address the agency’s feedback,” said Roy Baynes, Merck’s head of global clinical development, in the company’s statement.

Chronic cough, which is defined as a cough lasting more than two months, affects about 5% of adults in the U.S., according to Merck. Some of these people don’t respond to treatment of coughing triggers like asthma or gastroesophageal reflux. Merck targeted gefapixant toward those individuals, as well as those with unexplained coughing. There are no drugs approved specifically for either indication.

Canadian biotech Bellus Health is developing a drug that works similarly to gefapixant and, in December, released Phase 2b study results that it said showed treatment significantly reduced coughing frequency. The company, which in 2020 had reported its drug failed an earlier mid-stage trial, plans to start a Phase 3 study later this year.

Shares in Bellus fell by as much as 10% Monday morning, while Merck stock dropped by 3% amid a broader market sell-off.