The purpose of this study is to test the effectiveness of a new investigational medication, PTI-801, in treating cystic fibrosis (CF). The results of PTI-801 will be compared to those of a placebo, a capsule that looks like the investigational medication but does not contain an active drug substance. PTI-801 has not been approved by the Food and Drug Administration (FDA). Although it has been given to healthy adults, this is the first time it will be given to people with CF.

The majority of CF therapeutics are aimed at controlling symptoms and complications of CF. PTI-801 is being developed to treat the underlying mechanism of the disease. In laboratory tests, PTI-801 has been shown to work like one of the components of Orkambi®, a medication currently used to treat CF. In laboratory tests, PTI-801 has appeared to have an effect on cells from CF patients, adding to the effect of Orkambi®.