The Food and Drug Administration (FDA) has issued a Complete Response Letter (CRL) to Merck regarding the New Drug Application for gefapixant for the treatment of adults with refractory or unexplained chronic cough.

Gefapixant is an orally administered, selective P2X3 receptor antagonist. The application included data from the two phase 3 studies, COUGH-1 ( Identifier: NCT03449134) and COUGH-2 ( Identifier: NCT03449147), which evaluated the efficacy and safety of gefapixant in adults with refractory or unexplained chronic cough for at least 1 year. 

Findings from both studies showed that gefapixant 45mg twice daily met the primary endpoint demonstrating a statistically significant reduction in 24-hour cough frequency compared with placebo. Gefapixant was also associated with a significant reduction in awake coughs per hour (secondary endpoint), along with a clinically meaningful improvement in cough-related quality of life.

In the CRL, the FDA requested additional information related to measurement of efficacy. The letter was not related to the safety of gefapixant.

“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 Dr. Roy Baynes, senior vice president and head of global clinical development, chief medical officer, Merck Research Laboratories. “We believe there is a significant unmet need to help patients manage their chronic cough, as there are no available treatment options indicated in the US specifically for this condition.”


Merck provides US and Japan regulatory update for gefapixant. News release. Merck. Accessed January 24, 2022.