Influence of macrolide antibiotics on promotion of resistance in the oral flora of children

Background: The tong elimination half-life of azithromycin allows subinhibi tory serum and epithelial Lining fluid (ELF) concentrations over a period o f several weeks post treatment, which may have an impact on the emergence o f macrolide resistance. In this prospective, open-label, randomized study, four macrolides and the azalide azithromycin were studied for their Likelih ood to promote resistance in the oral flora of children with respiratory tr act infections. Patients and Methods: Children were randomly assigned to receive azithromyc in, clarithromycin, erythromycin, roxithromycin and josamycin. Throat swabs were obtained prior to treatment and weekly for 6 weeks. Minimum inhibitor y concentrations (MICs) for resistant strains were assessed by E-test and N ational Committee for Clinical Laboratory Standards (NCCLS) broth microdilu tion. Results: One week post treatment, up to 90% of children harbored macrolide- resistant strains in their oral flora. Except for azithromycin, the percent age of patients colonized by resistant organisms decreased to a rate of 17% for clarithromycin (10/60), erythromycin (2/12) and josamycin (2/12) and 3 3% for roxithromycin (4/12) after 6 weeks. In the azithromycin group, 85% ( 51/60) of patients were colonized by macrolide-resistant organisms after 6 weeks, 11.6% (7/60) of children suffered from reinfection. Conclusion: Azithromycin therapy appears to put selective pressure on the i nfective and native flora of children, promoting the carriage of macrolide- resistant strains.