Effects of amoxicilin/clavulanate or azithromycin on nasopharyngeal carriage of Streptococcus pneumoniae and Haemophilus influenzae in children with acute otitis media

The effect of antibiotic therapy on nasopharyngeal colonization by Streptoc occus pneumoniae and Haemophilus influenzae was evaluated in children diagn osed with acute otitis media. Children were randomly assigned to receive ei ther amoxicillin/clavulanate or azithromycin therapy, and nasopharyngeal sw abs were obtained for culture before and after starting therapy. Amoxicilli n/clavulanate therapy eradicated or suppressed all strains of S. pneumoniae susceptible to penicillin, 75% of strains with intermediate resistance, an d 40% of strains resistant to penicillin. Azithromycin therapy cleared two- thirds of azithromycin-susceptible strains of S, pneumoniae but none of azi thromycin-nonsusceptible strains. Selection for antibiotic-resistant strain s in individual children was not observed in children who received amoxicil lin/clavulanate therapy but was observed in 2 children who received azithro mycin therapy. Carriage of H. influenzae was also reduced by antimicrobial therapy but more so by amoxicillin/clavulanate. Antibiotic therapy does not directly increase the number of resistant strains in the population but, b y eradicating susceptible strains, allows greater opportunity for carriage and spread of resistant strains.