Potential mechanisms for failure to eradicate group A streptococci from the pharynx

Objective. To investigate the relative efficacy of orally administered cefa droxil and penicillin V in the treatment of group A streptococcal (GABHS) p haryngitis and the mechanism(s) responsible for failure of antimicrobial th erapy to eradicate GABHS from the pharynx. Study Design. A prospective, randomized clinical trial was conducted in fou r pediatric offices in which 462 patients with acute pharyngitis and positi ve culture for GABHS were randomly assigned to receive cefadroxil (n = 232) or penicillin V (n = 230). Results. Bacteriologic treatment success rates for patients in cefadroxil a nd penicillin groups were 94% and 86%, respectively. However, among patient s classified clinically as likely to have bona fide GABHS pharyngitis, ther e was no difference in bacteriologic treatment success rates in cefadroxil and penicillin groups (95% and 94%, respectively). Among patients classifie d clinically as likely to be streptococcal carriers, bacteriologic treatmen t success rates in cefadroxil and penicillin groups were 92% and 73%, respe ctively. The presence of beta-lactamase and/or bacteriocin-producing pharyn geal flora had no consistent effect on bacteriologic eradication rates amon g patients in either penicillin or cefadroxil treatment groups or among pat ients classified as having either GABHS pharyngitis or streptococcal carria ge. Conclusions. Neither beta-lactamase nor bacteriocin produced by normal phar yngeal flora are related to bacteriologic treatment failures in GABHS phary ngitis. Cefadroxil seems to be more effective than penicillin V in eradicat ing GABHS from patients classified as more likely to be streptococcal carri ers. However, among patients we classified as more likely to have bona fide GABHS pharyngitis, the effectiveness of cefadroxil and penicillin V seems to be comparable.