As prior data has suggested that discontinuation of Dorn or HTS may not alter lung function in PwCF on ETI, we examined relationships between changes in lung function (slope ppFEV₁) and changes in MPR for various medications. Among 112 PwCF with sufficient lung function data pre- and post-ETI, average ppFEV₁increased significantly in the post-ETI period (74.5±24.4% pre-ETI, 82.6±25.0% post-ETI, p<0.001). In the pre-ETI period, lung function declined slowly over time (slope ppFEV1 ‐0.8 ± 5.0%/year). In the post-ETI period, change in FEV1 over time remained negative (slope ppFEV1 ‐1.5 ± 6.1%/year) and was not statistically distinguishable from the pre-ETI period (p=0.34). While continued decline in lung function could reflect changes in adherence to inhaled medications, PwCF who had lung function decline post ETI (negative ppFEV₁ slopes) had similar MPRs for Dorn and HTS to those with preserved or improving lung function (positive slopes) (Fig 1B ). As an alternative analysis, ppFEV₁ slope did not correlate with changes in MPR for Dorn or HTS (Fig. 1C ). To account for possible confounding factors, we performed a multivariate analysis including age, initial ppFEV₁, and prior modulator use in the model along with changes in MPR for Dorn and HTS. Although age at start of ETI was correlated with slope ppFEV₁ post-ETI (r=0.4, p=0.02) in univariate analysis, no variables were significantly correlated in multivariate analysis.