Gut Imaging for Function & Transit in Cystic Fibrosis Study 2

This is a small pilot study to compare the effects of active drug (Tezacaftor/Ivacaftor with Ivacaftor) on the gut in people with CF.

Participants will be randomised to take active drug or matched placebo for 28 days then switch to the alternate drug after a 28 day washout period. Before participants commence treatment, they will have blood pressure and baseline blood tests.

Participants will attend once per treatment period for MRI scanning at the Sir Peter Mansfield Imaging Centre, after an overnight fast. On this day, participants will be asked to withhold any medicines directly altering bowel habit such as laxatives. They will continue to take pancreatic enzyme replacement therapy and other medications for CF.

The Investigators will use the same MRI protocol as described in GIFT-CF (NCT03566550). Participants will have their first MRI scan fasted. After the first scan, they will eat a first standardised meal . They will then have 7 MRI scans at half hourly intervals and 3 MRI scans at hourly intervals. Participants will be given a second standardised meal after their ninth MRI scan. Each MRI scan will last approximately 15 minutes. After each MRI scan, participants will complete a validated gastrointestinal symptom questionnaire (Gastrointestinal Symptom Rating Scale). In between scans, participants will have access to an adjacent room with Wifi and television access.

During the day, participants will have their lung function, blood pressure and blood tests taken. They will also provide a sputum and stool sample.

Infection control requirements mean that only 1 participant will attend for MRI scanning per day.

\*\*\*Amendment to study due to COVID-19\*\*\* From mid-March 2020, all face to face clinical research in the UK has been suspended (apart from studies directly related to the COVID-19 pandemic). Patients in the GIFT-CF 2 trial who had not yet completed the full trial protocol were therefore unable to continue. Funding for SymkeviTM (tezacaftor/ivacaftor and ivacaftor) in the UK was announced at the end of 2019 and some of the trial participants, who have not completed GIFT-CF 2, may be prescribed SymkeviTM by their CF team. It will therefore not be possible for them to complete the placebo controlled cross-over trial, once COVID restrictions are eased. We plan to mitigate the effects of COVID-related disruption by ensuring all trial participants have had the full, protocol-defined, scan sequence both on and off SymkeviTM. When restrictions are eased, we will invite participants who have been prescribed SymkeviTM by their CF centre to attend for scanning, if they have not previously had an "on treatment" scan. We will follow the same scanning protocol. We will ensure that adherence to SymkeviTM is good and they have received at least 21 days of treatment (as specified in the trial protocol). Our primary analysis will be on the patients who completed the trial per protocol but we will present a secondary analysis on all 12 patients, comparing outcome measures on SymkeviTM with their outcome measures previously recorded at baseline (off treatment). The personnel interpreting the MRI scans will be blind to whether they were performed on or off SymkeviTM - reducing the probability of observer bias.