This clinical trial is focused on studying Cystic Fibrosis, a genetic condition that affects the lungs and digestive system. The study will evaluate the effectiveness and safety of three investigational medications: Dirocaftor, Posenacaftor, and Nesolicaftor. These medications are taken as hard capsules and are designed to help improve lung function in people with cystic fibrosis. The trial will also include a placebo, which is a substance with no active medication, to compare the effects of the investigational drugs.

The purpose of the study is to assess how well these medications work over an 8-week period in adults aged 18 and older who have cystic fibrosis with specific rare genetic mutations. Participants will be randomly assigned to receive either the investigational medications or a placebo. The study is designed as a crossover trial, meaning that participants will receive both the investigational medications and the placebo at different times during the study. This helps researchers understand the effects of the medications more clearly.

Throughout the study, participants will have regular check-ups to monitor their health and any changes in their condition. These check-ups will include tests to measure lung function, sweat chloride levels, and body weight, as well as assessments of overall health and any side effects. The study aims to provide valuable information on the potential benefits and safety of Dirocaftor, Posenacaftor, and Nesolicaftor for people living with cystic fibrosis.