Selection of Antibiotic Resistance by Azithromycin and Clarithromycin in the Oral Flora

Resistance to antibiotics is a major public-health problem and studies linking antibiotic use and resistance have shown an association not a causal effect. Utilizing the newer macrolides, azithromycin and clarithromycin that are commonly prescribed for respiratory infections, we investigated the direct impact of antibiotic exposure on resistance at the individual level. 203 healthy cohorts were treated with azithromycin, clarithromycin, or a placebo in a randomised, double-blind trial. Pharyngeal swabs were collected pre- (day 0) and post-antibiotic administration (days 8, 14, 28, 42, 180) and proportions of macrolide-resistant streptococci (MRS) were determined at each time-point.