Study of Ivacaftor in Cystic Fibrosis Subjects Aged 6 to 11 Years With the G551D Mutation

Inclusion Criteria: * Weighing at least 15 kg * Confirmed diagnosis of cystic fibrosis (CF) and G551D mutation in at least 1 allele * Forced expiratory volume in 1 second (FEV1) of 40% to 105% (inclusive) of predicted normal for age, gender, and height (Knudson standards) at Screening * Able to swallow tablets * As judged by the investigator, parent or legal guardian and subject must have been able to understand protocol requirements, restrictions, and instructions, and the parent or legal guardian should have been able to ensure that the subject complied with, and was likely to complete, the study as planned * Parent or legal guardian must have signed the informed consent form and corresponding assent must be obtained from the subject * Willing to use at least 1 highly effective birth control method during the study * No clinically significant abnormalities that would have interfered with the study assessments, as judged by the investigator Exclusion Criteria: * History of any illness or condition that might confound the results of the study or pose an additional risk in administering study drug to the subject * Acute respiratory infection, pulmonary exacerbation, or changes in therapy for pulmonary disease within 4 weeks of Day 1 of the study * Abnormal liver function ≥ 3x the upper limit of normal * Abnormal renal function at Screening * History of solid organ or hematological transplantation * Ongoing participation in another therapeutic clinical study or prior participation in an investigational drug study within 30 days prior to Screening * Use of inhaled hypertonic saline treatment * Concomitant use of any inhibitors or inducers of cytochrome P450 3A4 (CYP 3A4)