Lack of influence of beta-lactamase-producing flora on recovery of group A streptococci after treatment of acute pharyngitis.

Because production of beta-lactamase by normal pharyngeal flora could account for penicillin treatment failure, we studied the effect of anaerobic and aerobic beta-lactamase-producing bacteria on bacteriologic outcome in acute group A beta-hemolytic streptococcal (GABHS) pharyngitis. We compared 10-day courses of orally administered phenoxymethyl penicillin and amoxicillin-clavulanic acid, using a randomized, single-blind treatment protocol. Eligible patients were 2 to 16 years of age and had culture-proven acute GABHS pharyngitis; 89 patients (43 penicillin, 46 amoxicillin-clavulanic acid) were compliant with therapy. beta-Lactamase-producing organisms were isolated before therapy from the throats of 67% of patients treated with penicillin and 63% treated with amoxicillin-clavulanic acid. Throat cultures after completion of therapy were positive for GABHS in 7 (7.9%) of 89 patients. The initial GABHS T type persisted (treatment failure) in only 4 (4.5%) of 89 patients, including 3 (6.5%) of 46 who received amoxicillin-clavulanic acid and in 1 (2.3%) of 43 who received penicillin (not statistically significant). Bacteriologic treatment failure was unrelated to recovery of beta-lactamase-producing bacteria at the time of enrollment or after treatment. We conclude that beta-lactamase production by normal pharyngeal flora does not fully explain the failure of penicillin therapy for acute streptococcal pharyngitis. Using an antibiotic effective against beta-lactamase-producing bacteria will not eliminate the problem of bacteriologic treatment failure.