Ivacaftor is the first Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) modulator to show an improvement in CFTR function and clinical benefit in participants with CF. Results from Phase 3 studies (NCT00909532 [Study 102] and NCT00909727 [Study 103]) showed that ivacaftor is effective in the treatment of participants with CF who have the G551D-CFTR mutation, as evidenced by sustained improvements in CFTR channel function (measured by reduction in sweat chloride concentration) and corresponding substantial, durable improvements in lung function, pulmonary exacerbations, respiratory symptoms, and weight gain. Ivacaftor was also well tolerated, as evidenced by the rates and reasons for premature discontinuation and results of safety assessments.