Long term clinical effectiveness of ivacaftor in people with the G551D CFTR mutation

•Ivacaftor led to long-term benefits in adults and children with the G551D mutation.•Adults and those with lower lung function had larger improvements in lung function.•Rate of lung function decline was higher in children compared with adults.•Ivacaftor resulted in sustained reductions in sweat chloride over 5 years.•Improvements in growth, quality of life, P. aeruginosa, and exacerbations were seen. The cystic fibrosis transmembrane conductance regulator (CFTR) potentiator, ivacaftor, was first approved for people with CF and the G551D CFTR mutation. This study describes the long-term clinical effectiveness of ivacaftor in this population. We conducted a multicenter, prospective, longitudinal, observational study of people with CF ages ≥6 years with at least one copy of the G551D CFTR mutation. Measurements of lung function, growth, quality of life, and sweat chloride were performed after ivacaftor initiation (baseline, 1 month, 3 months, 6 months, and annually thereafter until 5.5 years). Ninety-six participants were enrolled, with 81% completing all study measures through 5.5 years. This cohort experienced significant improvements in percent predicted forced expiratory volume in 1 second (ppFEV1) of 4.8 [2.6, 7.1] (p