Short Term Effects of Ivacaftor in Non-G551D Cystic Fibrosis Patients

This is a study of the short-term effects of ivacaftor on sweat chloride concentration and lung function in cystic fibrosis (CF) patients who fall outside current FDA approval. This new, first of its kind drug is approved for use only in CF patients with the G551D mutation in whom it safely confers considerable benefits. However, it is highly likely that CF patients with many other mutations can benefit similarly from this drug, some of whom can be identified by phenotype or genotype. We will enroll up to 30 CF subjects with clinical presentations in which there is one or more signs of residual CF channel function. The signs of residual function include: normal digestion, concentration of chloride in sweat between 55 and 85, or milder than expected CF disease in a CF patient with severe gene mutations. The primary outcome measure will be the difference in sweat chloride concentration measured in subjects on placebo and on ivacaftor. Secondary outcome measured will be lung function.