Ivacaftor in Subjects With Cystic Fibrosis Who Are Homozygous for the F508del-CFTR Mutation

Background: Ivacaftor (VX-770) is a cystic fibrosis transmembrane conductance regulator (CFTR) potentiator that was approved in the United States for the treatment of cystic fibrosis (CF) in patients >= 6 years of age who have a G551D mutation; however, the most prevalent disease-causing CFTR mutation, F508de1, causes a different functional defect. The objectives of this study were to evaluate the safety of ivacaftor in a larger population and for a longer time period than tested previously and to assess the efficacy of ivacaftor in subjects with CF who are homozygous for F508del-CFTR. Methods: This was a phase 2 study with a 16-week randomized (4:1), double-blind, placebo-controlled period (part A) and an open-label extension (part B) for subjects who met prespecified criteria. Results: Part A: The safety profile of ivacaftor was comparable to that of the placebo. The overall adverse event frequency was similar in the ivacaftor (87.5%) and placebo (89.3%) groups through 16 weeks. The difference in the change of FEV1 % predicted from baseline through week 16 (primary end point) between the ivacaftor and placebo groups was 1.7% (P =.15). Sweat chloride, a biomarker of CFTR activity, showed a small reduction in the ivacaftor Vs placebo groups of -2.9 mmol/L (P =.04) from baseline through week 16. Part B: No new safety signals were identified. The changes in FEV1, or sweat chloride in part A were not sustained with ivacaftor treatment from week 16 to week 40. Conclusions: These results expand the safety information for ivacaftor and support its continued evaluation. Lack of a clinical effect suggests that a CFTR potentiator alone is not an effective therapeutic approach for patients who have CF and are homozygous for F508de1-CFTR. Trial registry: ClinicalTrials.gov; No.: NCT00953706; URL: www.clinicaltrials.gov. CHEST 2012; 142(3):718-724