Two antibiotic regimens led to lasting increases in the proportion of resistant streptococci.
Antibiotic use and bacterial resistance have been linked through observational studies and animal experiments, but randomized trials directly demonstrating causality in humans have been lacking. Investigators randomized 224 healthy young adults to receive azithromycin (500 mg daily for 3 days), clarithromycin (500 mg twice daily for 7 days), or matching placebo regimens. Oropharyngeal cultures were taken at baseline, at the conclusion of treatment, and on days 14, 28, 42, and 180.
During treatment, the proportion of macrolide-resistant commensal streptococci increased from 26% to 86% in the azithromycin group and from 30% to 82% in the clarithromycin group. Between days 14 and 42, the proportion of resistant streptococci gradually declined i…