To evaluate the effect of ciprofloxacin on the pharmacokinetics (PK) of ivacaftor and on the pharmacokinetics of VX-661 when administered in combination with ivacaftor

Inclusion Criteria:

• Willing and able to comply with scheduled visits, treatment plan, study restrictions,laboratory tests, contraception guidelines, and other study procedures
• Healthy subjects, as defined by no clinically relevant abnormalities identified by a detailed medical history and full physical examination, including blood pressure and heart rate measurement, standard 12-lead ECG, and clinical laboratory tests.
• Body mass index (BMI) of 18.0 to 31.0 kg/m2, inclusive, and a total body weight >50 kg
• Female subjects of childbearing potential must have a negative serum pregnancy test at screening and at the Day -1 Visit.

Exclusion Criteria:

• History of any illness, clinical condition, or other factor that, in the opinion of the investigator or the subject's general practitioner, might confound the results of the study or pose an additional risk in administering study drug(s) to the subject
• Inability to swallow capsules, or inadequate venous access.
• History of febrile illness within 5 days before the first study drug dose
• A screen positive for hepatitis B surface antigen, hepatitis C virus antibody, or human immunodeficiency virus 1 or 2 antibodies.
• For female subjects: Pregnant or nursing subjects and female subjects of childbearing potential who are unwilling or unable to use an acceptable method of contraception as outlined in this protocol. For male subjects: Subject has a female partner who is pregnant, nursing, or planning to become pregnant during the study or within 120 days after the last study drug dose.
• Any condition possibly affecting drug absorption
• Abnormal renal function at screening