Changes in LCI in F508del/F508del patients treated with lumacaftor/ivacaftor: Results from the prospect study

The PROSPECT study, a post-approval observational study in the U.S., showed no significant changes in lung function as measured by spirometry with clinical initiation of lumacaftor/ivacaftor. A sub-study within the PROSPECT study assessed the lung clearance index (LCI), as measured by multiple breath washout (MBW), a measure of lung function demonstrated to be sensitive among people with normal spirometry. Participants performed MBW prior to clinically initiating lumacaftor/ivacaftor therapy and for one year of follow-up. Similar to the whole PROSPECT study, this sub-study cohort (N = 49) had no significant absolute or relative changes in FEV1% predicted at any time point. LCI, however, decreased (improved) by 0.81 units or 5.3% (95% CI -9.7, -0.9%) at 1 month, 0.77 units or 5.9% at 3 months, 0.67 units or 5.9% at 6 months, and 0.55 units or 4.3% at 12 months. These results demonstrate the utility of the LCI in assessing treatment effects of relatively modest size in a heterogenous study population. (C) 2020 Published by Elsevier B.V. on behalf of European Cystic Fibrosis Society.