Can an extra inhaler boost lung clearance in cystic fibrosis patients already on breakthrough drugs?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Able to provide informed consent * Age ≥ 18 at the time of screening * Diagnosis of cystic fibrosis (CF) * Regularly using elexacaftor/tezacaftor/ivacaftor (E/T/I) for ≥ 90 days * Forced Expiratory Volume in one second (FEV1) between 30% and 70%, inclusive, at time of screening * Denies active smoking or vaping * Clinically stable with no significant changes in health status within the 28 days prior to and including the screening visit * Patients on cycled inhaled antibiotics will need to be either on or off their antibiotic for 7 days prior to Visit 1 and not scheduled to cycle during the 2-week treatment period until after Visit 2 * Has no other conditions that, in the opinion of the Site Investigator/Designee, would preclude informed consent, make study participation unsafe, complicate interpretation of study outcome data, or otherwise interfere with achieving the study objectives Exclusion Criteria: * Use of an investigational drug within 28 days prior to and including the screening visit * Unable or unwilling to withhold hypertonic saline (HS) for 4 weeks (2 weeks prior to Visit 1 and 2 weeks between Visit 1 and Visit 2) * Unable or willing to withhold dornase alfa and bronchodilators on the morning of Visit 1 and Visit 2, until completion of study procedures * Initiation of new chronic CF pulmonary therapy (e.g. dornase alfa, azithromycin, inhaled antibiotic) within 28 days prior to and including the screening visit * No acute use of antibiotics (oral, inhaled, or intravenous) or acute use of systemic corticosteroids for respiratory tract symptoms within 28 days prior to and including the screening visit. * No chronic use of oral corticosteroids \> 10 mg of prednisone or equivalent daily * Unable to tolerate albuterol or other bronchodilator * History of intolerance to HS or inhaled mannitol * Pregnancy or breast feeding * Have had more than 2 chest computed tomography (CT) in the past year or a combination of procedures that are believed to have exposed the subject's lungs to \>150 millisievert (mSv) * History of significant hemoptysis (\>60 mL) in the last three months