WEDNESDAY, Feb. 26, 2020 — Anywhere from 4% to 10% of adults have troublesome chronic cough, defined as an unexplained cough lasting more than eight weeks. But a new drug may offer some long-sought relief.

Reporting Feb. 25 in The Lancet Respiratory Medicine, British researchers said the experimental drug, called gefapixant, blocks a cellular receptor that’s key to the cough reflex.

“Many patients with a chronic cough are driven to seek treatment because of the significant negative impact it can have on their quality of life, but at the moment physicians are unable to help,” noted study leader Jacky Smith, a professor at the University of Manchester, in England.

This “is the first study to report a treatment that is safe and effective over the longer term,” Smith said in a journal news release. She added that “phase 3 trials are already underway with an even larger group of people and over a longer time frame.”

The trial was funded by the drug’s maker, Merck, and involved 253 American and British participants. All had suffered from an unexplained or untreatable cough that had lasted for an average of almost 15 years. Three-quarters were women, most (70%) had never smoked, and patients averaged 60 years of age.

The patients received either a “dummy” placebo or gefapixant twice a day for three months. Those who received the drug were given one of three doses: 7.5 milligrams (mg), 20 mg, or 50 mg.

Everyone was asked to keep a “cough diary,” and they also wore a device that recorded their coughing over a 24-hour period.

Before the study began, patients coughed about 24 to 29 times an hour. But after the trial period, the placebo group coughed 18 times an hour, compared with 11 coughs an hour among patients in the 50 mg gefapixant group — a 37% difference.

The patients in the 7.5 mg and 20 mg gefapixant groups had slightly lower rates of coughing than those in the placebo group, but the differences were not statistically significant, the study authors noted.

The most common side effect among patients in the study was a change in their sense of taste.

Two experts unconnected to the study said any drug that helps ease chronic cough is long overdue.

“Whoever creates the treatment to control chronic cough will help millions of patients lead a more comfortable life,” said Dr. Theodore Maniatis, medical director at Staten Island University Hospital in New York City. He said that once the usual suspects for cough — asthma, acid reflux and others — are ruled out, “patients remaining are assumed to have a hypersensitive cough reflex mechanism.”

Gefapixant “acts by antagonizing the activity of one of the receptors (a group of chemicals at nerve endings) and thereby decreasing the transmission of nerve impulses to the cough centers,” Maniatis explained.

He hopes the new drug proves successful because, “in the past, the only treatment that was minimally successful was narcotic cough suppressants.”

Dr. Margarita Oks is a pulmonologist at Lenox Hill Hospital in New York City. She noted that there was a strong placebo effect in the study, but “the authors adjusted their results for the placebo effect,” strengthening the validity of the results.

“The drug under investigation is too new to be sure of its effectiveness and its side effects,” Oks said, “but there are some promising results so far.”

More information

Harvard Medical School has more on chronic cough.

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