Oral Azithromycin Use and the Recovery of Lung Function from Pulmonary Exacerbations Treated with Intravenous Tobramycin or Colistimethate in Adults with Cystic Fibrosis

Rationale: The potential of azithromycin to alter the antimicrobial and clinical benefits of inhaled tobramycin in CF patients has been previously reported. The potential interaction between azithromycin and intravenous antibiotics in the treatment of pulmonary exacerbations is unknown. Objectives: To determine if chronic azithromycin use as a concomitant therapy associated with change in lung function after receiving IV antibiotic regimens including tobramycin or colistimethate. Methods: Retrospective cohort study evaluating the effect of azithromycin with IV tobramycin or colistimethate in adult CF patients treated for a pulmonary exacerbation. The primary outcome was relative lung function recovery (FEV1) following exacerbation treatment. Generalized estimating equations were applied to account for repeated events with independent correlation structures and robust standard errors, incorporating several confounders. Results: 220 exacerbation events occurred in 121 patients in the tobramycin group (47% u...