PENICILLIN TOLERANCE AND TREATMENT FAILURE IN GROUP-A STREPTOCOCCAL PHARYNGOTONSILLITIS

Failure of treatment of group A streptococcal pharyngitis and tonsilli tis is well documented. One of the possible explanations for treatment failure is penicillin tolerance in group A streptococci. Reports on t he prevalence of penicillin tolerance among group A streptococci (0-10 0%) and the presumed relationship with therapeutic failure vary consid erably. Therefore, it appears worthwhile to review pharyngotonsillitis studies, devoting special attention to the variables of MIC-MBC labor atory determinations such as inoculum preparation, composition and vol ume of test medium, and the criteria used to define penicillin toleran ce. Alternative methods (gradient-replica plate method, beta-lactamase disk test, time-kill assay, and cell-lysis assay) are discussed. It i s concluded that technical factors and the definitions used influenced the reported rates of penicillin tolerance. The epidemiological data suggest that tolerance is not limited to a single streptococcal seroty pe. Furthermore, there is not sufficient data to support a correlation between in vitro penicillin tolerance of group A streptococci and tre atment failure, either in clinical cases or in animal studies. On the other hand, evidence to exclude penicillin tolerance as a cause of tre atment failure is also not available. Therefore, at present, penicilli n tolerance cannot be ruled out as a cause of penicillin treatment fai lures.