Failure of two macrolide antibiotics to prevent post-extraction bacteraemia.

Two macrolide antibiotics, erythromycin and josamycin, were compared in a double-blind trial to examine their efficacy in the prevention of post-dental extraction bacteraemia in a group of healthy patients. An in vitro blood culture system was used. Isolates of streptococci were identified to species level. Minimum inhibitory concentrations (MICs) of erythromycin and of josamycin for each isolate were estimated by an agar dilution technique, with controls. Levels of drug in the serum of volunteers and of patients were assayed after oral doses of the macrolide antibiotics. Levels found achieved early peaks and satisfactory concentrations for activity against streptococci. Within the specified parameters, the results demonstrated that the antibiotics failed to prevent survival in blood culture of various strains of streptococci for up to 24 hours following collection of the blood. It is recommended that an alternative antibiotic to either erythromycin or to josamycin be used to achieve prophylaxis against streptococci in infective endocarditis risk patients who are allergic to penicillin.