Quantifying Long-Term Changes in Lung Function and Exacerbations after Initiation of Azithromycin in Cystic Fibrosis

Rationale: In cystic fibrosis, information on the efficacy of azithromycin past 12 months of treatment is still scarce. Objectives: The study sought to quantify the changes in lung function and the number of intravenous antibiotic courses (IVACs) after initiation of azithromycin in patients included in the French Cystic Fibrosis Registry. Methods: The study followed 1,065 children and 990 adults from 2 years before to 5 years after long-term azithromycin treatment initiated between 2001 and 2011. Mixed change-point models were used to quantify the changes in the forced expiratory volume (FEV) in 1 second and the yearly number of IVACs. Results: In the year of treatment initiation, the mean FEV was significantly higher than expected (+1.6%, P = 0.007 in children; +1.3%, P = 0.02 in adults). The decline of the FEV over time was less marked after than before treatment initiation (slope difference = +0.7% per year [P = 0.03] in children and +0.6% per year [P = 0.06] in adults). The mean increase in the yearly number of IVACs was lower after than before treatment initiation. The rate ratio quantifying the effect on the mean increase was 0.93 (95% confidence interval = [0.88-0.99]; P = 0.02) in children and 0.95 (95% confidence interval = [0.90-1.01]; P = 0.08) in adults. Conclusions: In children, long-term azithromycin treatment was associated with immediate and sustained beneficial changes in lung function and sustained beneficial changes in the frequency of pulmonary exacerbations. In adults, it was associated with immediate beneficial changes in lung function.