A new study published in Nature Microbiology found that use of the antibiotic azithromycin was “associated with potentially harmful changes in the upper respiratory microbiome and increased expression of antibiotic-resistance genes after only one day of exposure.” CIDRAP has the news.

Nearly 75% of hospitalized COVID patients received antibiotics on admission in the early days of the pandemic. Azithromycin was touted in a now-retracted study as possibly improving outcomes in COVID patients when used in combination with hydroxychloroquine. Use continued for several months even after no benefits were found.

The observational study analyzed nasal swabs of 1,164 adults hospitalized for COVID. 31.4% were treated “empirically with azithromycin and other antibiotics, 40.7% received no antibiotics, and 27.8% received antibiotics other than azithromycin.” The patients who had received azithromycin “had a different mix of bacteria in their upper airway, with a reduced presence of some harmless bacteria and an increased presence of pathogenic species.” They also found the patients exposed to azithromycin had more “’delectably expressed,’ or active, macrolide resistance genes than the other groups of patients had.”

Azithromycin is used to “prevent bacterial infections in people with chronic obstructive pulmonary disease and cystic fibrosis, lung transplant patients, and HIV.”