Impact of prior antibiotic therapy for acute otitis media on pathogen susceptibility in a subsequent episode

Prior antibiotic treatment may cause a shift toward resistant bacterial str ains in subsequent infections due to selection pressure. This analysis was conducted to investigate the potential impact of prior antimicrobial therap y on susceptibility of Streptococcus and Haemophilus influenzae isolates to penicillin, ampicillin, cefprozil, and clarithromycin in a prospective, mu lticenter trial of treatment: for acute otitis media (AOM). A subset of chi ldren from that trial (n = 113) had received prior AOM therapy with amoxici llin or amoxicillin/clavulanate, a macrolide, or a cephalosporin within 1 y ear before study entry and had a pathogen isolated by tympanocentesis at th e pretreatment visit. One hundred forty-two pathogens that are known etiolo gic agents of AOM were identified from the previously treated children; of these pathogens, 123 (87%) were S pneumoniae or H influenzae. For S pneumon iae (n = 68), 50% were penicillin-susceptible isolates, 12% were intermedia tely penicillin resistant, and 38% were penicillin resistant; 64% of the H influenzae isolates (n = 55) produced beta-lactamase. If the most recent pr ior AOM therapy was amoxicillin or amoxicillin/clavulanate (n = 57 isolates ), the rates of resistance of the S pneumoniae or H influenzae isolates to penicillin (36.4% resistance), ampicillin (58.3%), clarithromycin (3.7%), a nd cefprozil (10.5%) differed significantly; if prior therapy was a macroli de (n = 10 isolates), resistance to penicillin (50.0%), ampicillin (50.0%), clarithromycin (40.0%), and cefprozil (0%) differed significantly; and if prior therapy was a cephalosporin (n = 56 isolates), resistance to penicill in (38.7%), ampicillin (56.0%), clarithromycin (19.6%), and cefprozil (1.8% ) differed significantly. Prior antibiotic therapy may influence pathogen s usceptibility in recently treated AOM in children. Such information should be considered in the subsequent selection of antimicrobial therapy. Prospec tive clinical trials specifically designed to monitor resistance rates are recommended to investigate these findings further.