The single treatment group will enroll adult subjects with CF currently on stable KALYDECO® background therapy for a minimum of 3 months at the time of randomization. Subjects will be randomized to either PTI-428 or placebo. Each dose will be administered once daily (QD) for a total of 14 Days. The subjects will continue treatment with KALYDECO® throughout the study.
The trial will consist of a single treatment group enrolling adult subjects with CF on background therapy with KALYDECO®. Approximately 16 subjects will be enrolled.