Vertex Pharmaceuticals announced that it received a Complete Response Letter from the U.S. Food and Drug Administration (FDA) for its supplemental New Drug Application (sNDA) for the use of KALYDECO® (ivacaftor) in people with cystic fibrosis (CF) ages 2 and older who have one of 23 residual function mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The FDA determined that it cannot approve the application in its present form. Vertex plans to meet with the FDA to determine an appropriate path forward.