C61-10 Evaluating FEV1 Change in Relation to Acute Respiratory Events in Pediatric Cystic Fibrosis Patients Undergoing Elexacaftor/Tezacaftor/Ivacaftor Therapy

Background Elexacaftor/tezacaftor/ivacaftor (ETI) has transformed cystic fibrosis (CF) care by improving lung function and reducing pulmonary exacerbations. Whether the pattern of lung function decline and recovery during acute respiratory events (AREs) in pediatric patients differs before and after initiation of ETI is currently unknown. This study evaluates absolute change in percent predicted FEV1 (ppFEV1) during and after AREs in children with CF receiving ETI. Methods This retrospective chart review included children aged 6–17 years with confirmed CF followed between 2018 and 2024 who experienced at least one ARE while on ETI. AREs were categorized per Perrem et al (2021) [1]. Data was captured from two years pre-ETI initiation to the end of 2024. Baseline ppFEV1 was defined as the best in the prior 6 months. Outcomes included ppFEV1 change from baseline to time of event, and ppFEV1 recovery at the next follow-up visit. Mixed-effects linear regression models accounting for repeated measures within an individual were used to assess ppFEV1 trends. Results Among the 67 included participants, 58% were female, with a mean (SD) age at ETI initiation of 10.8 (3.3) years. Mean (SD) follow-up time was 1.4 (0.6) years pre-ETI and 2.2 (0.8) years post-ETI. Mean (SD) ppFEV1 was 104.8% predicted (13.8) at ETI initiation. The overall proportion of hospital encounters that were categorized as AREs decreased from 36.8% pre-ETI to 23.4% post-ETI (p < 0.001). Among the AREs, untreated acute cough events rose from 23% to 35%.The overall change in ppFEV1 from baseline to start of event was similar between time periods (-7.0% vs -7.0 % predicted; Δ 0.05% predicted, 95% CI -2.4, 2.5). The proportion of events that returned to 90% of baseline ppFEV1 was higher post-ETI (81% vs 90%; p = 0.04). Conclusions ETI was associated with a reduction in the proportion of symptomatic hospital encounters. Compared to pre-ETI, fewer AREs are being treated with antibiotics. Drops in FEV1 with AREs appear to be similar pre- and post-ETI. While rates of lung function recovery were higher post ETI, overall recovery was still incomplete suggesting that acute respiratory events, though less frequent, may still be of clinical significance in children with CF on ETI therapy. References [1] Perrem L, Stanojevic S, Shaw M, et al. Lung clearance index to track acute respiratory events in school-age children with cystic fibrosis. Am J Respir Crit Care Med 2021;203:977–86. This abstract is funded by: None