IN-VITRO ACTIVITY OF AZITHROMYCIN (CP-62,993) AGAINST CHLAMYDIA-TRACHOMATIS AND CHLAMYDIA-PNEUMONIAE

The in vitro susceptibilities of 49 strains of Chlamydia trachomatis a nd 3 strains of Chlamydia pneumoniae to azithromycin and tetracycline or doxycycline were determined. The MIC of azithromycin ranged from le ss-than-or-equal-to 0.06 to 1.0 mug/ml, the MIC of tetracycline ranged from 0.03 to 0.12 mug/ml, and the MIC of doxycycline ranged from 0.01 5 to 0.06 mug/ml against C. trachomatis. The MIC ranges for C. pneumon iae were 0.12 to 0.25 mug/ml for azithromycin and 0.06 to 0.12 mug/ml for tetracycline. All minimal chlamydicidal concentrations were either equal to the MIC or one or two dilutions higher. No strains resistant to these antibiotics were detected. In vitro activity shows that azit hromycin is highly active against C. trachomatis and C. pneumoniae.