CPET in CF Patients With One G551D Mutation Taking VX770

The Alfred CF Service is ready to initiate therapy with VX-770 in it's cohort. Investigators therefore have an opportunity to examine correlates between improvements in lung function, exercise capacity, inflammatory markers and indices of wellbeing in CF that may not be repeatable in a single cohort.

Investigators propose a double-blind, placebo-controlled cross-over study of 20 patients currently awaiting initiation of ivacaftor therapy. Patients enrolled in the study will be asked to undergo screening (day -28), and baseline assessments (day 0) and re-assessment studies (day 28) after treatment period 1, followed by baseline assessment at the beginning of treatment period 2 (day 56) and at the conclusion of treatment period 2 (day 84). A further assessment (day 224) will be performed 140 (+/-7) days following commencement on open label Ivacaftor.

After satisfying eligibility criteria, subjects will be randomly assigned to initial active treatment or placebo following a 4 week run-in period. After completion of period 1 and a 4 week washout period, subjects will cross-over to the alternative treatment. After 4 weeks of period 2, subjects will undergo final assessment as shown in the diagram below. However participants choosing not to continue taking ivacaftor in a Named Patient Program or another similar program run by Vertex Pharmaceuticals, Inc., ('Vertex'), at the end of the study period will be required to undergo a Safety Follow-Up visit 28 days after the final dose of study drug. Safety Follow-Up assessments will not include the CPET.