A Study to Evaluate the Safety, Pharmacokinetics, and Pharmacodynamics of Ivacaftor in Subjects With Cystic Fibrosis Who Are Less Than 24 Months of Age and Have a CFTR Gating Mutation

Inclusion Criteria:

- Confirmed diagnosis of CF by sweat chloride value or CF mutation criteria.

- Must have 1 of the following 9 CFTR mutations on at least 1 allele: G551D, G178R,
S549N, S549R, G551S, G1244E, S1251N, S1255P, or G1349D.

- Hematology, serum chemistry, and vital signs results at screening with no clinically
significant abnormalities that would interfere with the study assessments, as judged
by the investigator.

Exclusion Criteria:

- History of any illness or condition that, in the opinion of the investigator, might
confound the results of the study or pose an additional risk in administering study
drug to the subject

- Colonization with organisms associated with a more rapid decline in pulmonary status
at screening

- History of abnormal liver function or abnormal liver function at screening

- History of solid organ or hematological transplantation

- 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 before
screening

- Hemoglobin (Hgb) <9.5 g/dL at screening

- Chronic kidney disease of Stage 3 or above

- Presence of a non-congenital or progressive lens opacity or cataract at Screening

Other protocol defined Inclusion/Exclusion Criteria may apply.