Impact of Treating Small and Large Declines in Lung Function in Cystic Fibrosis

Background: The benefit of antibiotic treatment of acute drops in FEV 1 percent predicted (FEV 1 pp) has been clearly established, but data from the early 2000’s showed inconsistent treatment. Further, there is no empirical evidence for what magnitude of drop is clinically significant. Methods: : We used data from the CF Foundation Patient Registry (CFFPR) from 2016-2019 to determine the association between treatment (any IV antibiotics, only oral or newly prescribed inhaled antibiotics, or no antibiotic therapy) following a decline of ≥5% from baseline FEV 1 pp and return to 100% baseline FEV 1 pp days using multivariable logistic regression including an interaction between the magnitude of decline and treatment category. Results: : Overall, 16,495 PWCF had a decline : 16.5% were treated with IV antibiotics, 25.0% non-IV antibiotics, and 58.5% received no antibiotics. Antibiotic treatment was more likely for those with lower lung function, history of a positive PA culture, older age and larger FEV 1 decline (p<0.001). Treatment with IV antibiotics or oral/inhaled antibiotics was associated with a higher odds of recovery to baseline compared to no treatment across all levels of decline, including declines of 5-10%. Conclusions: : A large proportion of acute drops in FEV1 pp continue to be untreated, especially in younger patients and those with higher baseline lung function. Acute drops as small as 5% predicted are less likely to be recovered if antibiotic treatment is not prescribed. These findings suggest the need for more aggressive antimicrobial treatment of acute drops in FEV 1 , including those of a magnitude previously believed to be associated with self-recovery.