Merck announced that the U.S. Food and Drug Administration (FDA) has issued a Complete Response Letter (CRL) regarding Merck's New Drug Application (NDA) for gefapixant, the investigational, non-narcotic, orally administered selective P2X3 receptor antagonist, under development for the treatment of refractory chronic cough (RCC) or unexplained chronic cough (UCC) in adults. In March 2021, Merckannounced that the FDA accepted the company's NDA for gefapixant. In the CRL, the FDA requested additional information related to measurement of efficacy.

The CRL was not related to the safety of gefapixant. Merck is reviewing the letter and will meet with the agency to discuss next steps. Last week, the Japan Ministry of Health, Labor and Welfare (MHLW) approved LYFNUA® (gefapixant) Tablets 45 mg for adults with refractory or unexplained chronic cough.

In Japan, LYFNUA is the planned trademark for gefapixant; the trademark for gefapixant in other countries has not been approved. Outside of Japan, gefapixant is an investigational treatment and is still under review by other regulatory bodies.