[Comparative in vitro activity of new oral macrolides against Streptococcus pyogenes strains].

Some recently introduced macrolides have several clinical advantages over erythromycin. Azithrommcin, a prototype of these new macrolides could be a good alternative for the treatment of streptococcal pharyngitis, even over penicillin, whose failure rate can be as high as 30%. The aim of this study was to evaluate the in vitro susceptibility of 120 strains of S pyogenes isolated between 1990 and 1992 (40 per year), from diverse infections (specially tonsillitis). We determined Minimal Inhibitory Concentrations (MIC) of azithromycin, clarithromycin, roxithromycin, erythromycin and penicillin using the agar dilution method and the Minimal Bactericidal Concentration (MBC) by tube dilution for azythromycin and erythromycin. The MIC 90 for the new macrolides ranged from 0.03 to 0.12 microgram/ml, and was 0.03 microgram/ml for erythromycin and penicillin (not different). All strains were susceptible to all antibiotics and the date of isolation did not influence susceptibility. The MBC for azithromycin was 0.12 microgram/ml (identical to its MIC), which demonstrates the bactericidal effect of this antibiotic. It is concluded that this in vitro data supports the potential role of these new macrolides in the treatment of streptococcal infections.