Study of Ataluren in Nonsense Mutation Cystic Fibrosis (ACT CF)

This study is to enroll 208 subjects (184 fully evaluable) with nonsense-mutation-mediated CF who are at least 6 years of age and have an forced expiratory volume in 1 second (FEV1) \>= 40% and \<= 90% of predicted. Subjects will be stratified based on age, inhaled antibiotic use, and baseline FEV1, and will be randomized in a 1:1 ratio to receive oral ataluren administered 3 times per day (TID) at respective morning, midday, and evening doses of 10-, 10-, and 20-mg/kg or placebo. Based on the results of a previously conducted study, patients treated with chronic inhaled aminoglycosides (including TOBI) will not be eligible for participation. Spirometry measurement at the screening visit will establish patient eligibility for inclusion based on lung function. FEV1 stability will be assessed during the approximately 4-week screening period, at the conclusion of which patients will be required to demonstrate a relative change in %-predicted FEV1 of less than 15% when compared to the screening value. Assessments will be performed every 8 weeks, depending upon the outcome measure.