Effect of antimicrobial therapy with amoxicillin and cefprozil on bacterial interference and beta-lactamase production in the adenoids.

To compare the effects on the bacterial flora of the adenoids of antimicrobial therapy with amoxicillin or cefprozil, we enrolled in a prospective randomized study 60 children scheduled for elective adenoidectomy because of recurrent otitis media. They were randomized before surgery into 3 groups of 20 patients each: a no-therapy group, and groups with 10 days of either amoxicillin or cefprozil therapy. Core adenoid materials were quantitatively cultured for aerobic and facultative bacteria. The in vitro ability of alpha-hemolytic streptococci (AHS) to inhibit the growth of non-type B Haemophilus influenzae and Streptococcus pneumoniae was determined. The number of organisms in adenoids obtained from patients treated with either antibiotic was reduced as compared to that in adenoids from controls. However, in patients treated with amoxicillin, a significant decline in the number of AHS, and an increase (in Staphylococcus aureus) or no change in the number of other beta-lactamase-producing bacteria (BLPB) was noted. In contrast, in those treated with cefprozil, no change was noted in the frequency of recovery of AHS, and the number of BLPB decreased. Interfering AHS were more often recovered in patients treated with cefprozil. We conclude that the adenoids contain more interfering AHS after therapy with a second-generation oral cephalosporin (cefprozil) than after amoxicillin therapy. This study suggests a potential beneficial effect of using an antimicrobial that selectively spares interfering AHS while inhibiting BLPB.