Two-part study to assess CTP-656 dosed as a solid oral dosage form versus Kalydeco and multiple-ascending doses of CTP-656 dosed for 7 days.

This two-part study will assess in healthy male and female subjects a solid oral dose formulation of CTP-656 vs. Kalydeco® and the safety, tolerability and pharmacokinetic profiles of escalating CTP-656 solid oral doses following 7 days of dosing. In Part B, three doses of CTP-656 ranging from 75 mg up to 300 mg per day will be studied.

Inclusion Criteria:

• Healthy adults between 18 and 50 years of age, inclusive
• Body weight ≥ 50 kg and BMI within the range of 18 to 30 kg/m2, inclusive, at screening

Exclusion Criteria:

• History of clinically significant central nervous system (eg, seizures), cardiac, pulmonary, metabolic, renal (including nephrolithiasis), hepatic, including history of Gilbert's syndrome or gastrointestinal (GI) conditions
• PR interval ≥ 220 msec or QRS duration ≥ 120 msec or QTcF interval > 450 msec obtained at screening visit or prior to the first dose of study drug
• Liver function tests greater than the upper limit of normal.
• Positive blood screen for human immunodeficiency virus (HIV antibody), hepatitis B virus surface antigen, or hepatitis C virus antibody at screening
• Urinalysis positive for greater than trace blood, protein or glucose
• A positive screen for alcohol, drugs of abuse, or tobacco use.
• Inability to comply with food and beverage restrictions during study participation.
• Donation or blood collection or acute loss of blood prior to screening.