This study is designed to evaluate the effect of multiple doses of lumacaftor in combination with ivacaftor on cardiac repolarization, as detected by QT/QTc interval corrected for heart rate in healthy subjects.

Inclusion Criteria:

• Subjects must be willing and able to comply with scheduled visits, treatment plan, lifestyle guidelines, laboratory tests, contraceptive guidelines, and other study procedures.
• Subjects must be healthy, as defined by no clinically relevant abnormalities identified by a detailed medical history, physical examination, including blood pressure and pulse rate measurement, and 12 lead ECG.
• Subjects must weigh >50kg

Exclusion Criteria:

• Abnormal renal function at Screening
• Plasma donation within 7 days before first study drug dose or blood donation of 1 pint (500mL) within 56 days before first study drug dose
• Positively screen for Hepatitis B, Hepatitis C, HIV
• Known hypersensitivity or prior adverse reaction to moxifloxacin or other quinolones
• Any condition possibly affecting drug absorption (e.g., gastrectomy, or other gastrointestinal tract surgery, except appendectomy or cholecystectomy or polypectomy) or regular use of acid-lowering therapies (H2 blockers, proton pump inhibitors, and antacids).
• Female subjects who are pregnant, nursing, or planning to become pregnant during the study or within 90 days of the last study drug dose and female subjects of childbearing potential who are unwilling or unable to follow the contraceptive guidelines from at least 14 days before the first study drug dose.
• Male subject who has a female partner who is pregnant, nursing, or planning to become pregnant during the study or within 90 days of the last study drug dose; male subjects who are unwilling or unable to follow the contraceptive guidelines