No USFDA approval for Merck cough drug Gefapixant

The FDA's decision was not related to the drug's safety, Merck added.

The drugmaker said it would meet with the agency to discuss the next steps, without disclosing further details about the timeline. Shares of the company were down about 2.3% at $78.10.

The agency's decision could push back the approval of the oral drug gefapixant by several months, potentially helping Canada's Bellus Health Inc play catch up with its rival treatment candidate, BLU-5937.

"This setback could delay the launch for gefapixant potentially by six months to one year if no additional clinical trials are needed, and longer if another study is requested," Justin Zelin, analyst at BTIG, wrote in a note.

Meanwhile, Bellus in December reported positive results for BLU-5937 in a mid-stage study and the company had said it would start a late-stage trial in the second half of this year.

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Gefapixant and BLU-5937 target patients who have refractory chronic cough (RCC) which persists after the treatment of underlying health conditions such as asthma.

Chronic cough, which lasts more than eight weeks, is estimated to affect about 5% of adults in the United States, Merck said. RCC is a large target market with about nine million patients in the country and another nine million in Europe, according to Zelin.

Last week, Japan's health regulator approved gefapixant tablets for adults with refractory or unexplained chronic cough, to be marketed under the brand name Lyfnua.