Patients with cystic fibrosis (CF) who had pulmonary exacerbations treated with concomitant azithromycin and tobramycin had worse outcomes than those treated with tobramycin alone, according study results published in the Annals of the American Thoracic Society.

Researchers screened medical records in the CF Foundation Patient Registry-Pediatric Health Information System for patients aged 6 to 21 years with CF who were hospitalized for pulmonary exacerbations and treated with tobramycin. These records were retrospectively reviewed to determine if differences in outcomes existed between patients treated with concomitant azithromycin and tobramycin or tobramycin alone.

Of the 10,660 patients included in the dataset, there were 2294 (totaling 5022 pulmonary exacerbations) who were treated with tobramycin. Of those 5022 exacerbations, 2247 were treated with concomitant azithromycin and tobramycin.

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When azithromycin was used to treat patients, there was a significantly lower absolute improvement in percent predicted forced expiratory volume in 1 second (ppFEV1). Additionally, those patients had lower odds of returning to ≥90% of baseline ppFEV1, (odds ratio, 0.79; 95% CI, 0.68-0.93; P =.003) and a shorter time to next pulmonary exacerbations requiring intravenous antibiotics (hazard ratio, 1.22; 95% CI, 1.14-1.31; P <.001) compared to tobramycin without concomitant azithromycin.

“Concomitant [azithromycin] and [intravenous] tobramycin use for in-hospital pulmonary exacerbation treatment was associated with poorer clinical outcomes than treatment with [intravenous] tobramycin without [azithromycin],” the study authors wrote. “These results support the hypothesis that an antagonistic relationship between these two medications might exist.”


Cogen JD, Faino AV, Onchiri F, et al. Effect of concomitant azithromycin and tobramycin use on cystic fibrosis pulmonary exacerbation treatment. Ann Am Thorac Soc. Published online August 18, 2020. doi:10.1513/AnnalsATS.202002-176OC