
    low enrollment.
  
['cystic fibrosis']
['ivacaftor', 'placebo']

        Inclusion Criteria:

          -  Male or female with confirmed diagnosis of CF.

          -  Must have 1 of the following CFTR gating mutations on at least 1 allele: G551D, G178R,
             S549N, S549R, G551S, G1244E, S1251N, S1255P, or G1349D.

          -  Hematology, serum chemistry, and coagulation at Screening with no clinically
             significant abnormalities or concomitant diagnosis that would interfere with the LCI
             and CT scan study assessments, as judged by the investigator.

        Exclusion Criteria:

          -  An acute upper or lower respiratory infection, pulmonary exacerbation, or changes in
             therapy (including antibiotics) for pulmonary disease within 4 weeks before Day 1

          -  Any clinically significant laboratory abnormalities at the Screening Visit that would
             interfere with the study assessments or pose an undue risk for the subject (in the
             opinion of the investigator)

          -  Abnormal liver function, at Screening, defined as ≥3 × upper limit of normal (ULN), of
             any 3 or more of the following: serum aspartate transaminase (AST), serum alanine
             transaminase (ALT), gamma-glutamyl transpeptidase (GGT), serum alkaline phosphatase
             (ALP), and total bilirubin

          -  History of solid organ or hematological transplantation

          -  Any clinically significant "non-CF-related" illness within 2 weeks before Day 1

          -  Use of any moderate or strong inducers or inhibitors of cytochrome P450 (CYP) 3A
             within 2 weeks before Day 1

          -  Participation in a clinical study involving administration of either an
             investigational or a marketed drug within 30 days or 5 terminal half-lives (whichever
             is longer or as determined by the local requirements) before Screening
      