Penicillin and Erythromycin Concentrations in Tonsils: Relevance to Treatment Failures in Streptococcal Pharyngitis

Penicillin and erythromycin concentrations were measured in sera and tonsils of children undergoing tonsillectomy. For two hours after the intramuscular administration of potassium penicillin G (5,000 units/kg), the levels of penicillin in tonsil were consistently greater than the minimal inhibitory concentrations (MIC) of most group-A, β hemolytic streptococci. Antibiotic was not detected in six of ten specimens obtained four to six hours after single or multiple doses of orally administered phenoxymethyl penicillin. Tonsillar levels of erythromycin were greater than the MIC for group-A, β hemolytic streptococci in eight of ten specimens obtained four to seven hours after single or multiple doses of orally administered erythromycin estolate. Data correlating tonsillar antibiotic levels, MIC values, and in vitro streptococcal kill curves may have relevance to relapse and treatment failures in streptococcal pharyngitis.