In vitro evaluation of activities of azithromycin, clarithromycin and sparfloxacin against Chlamydia trachomatis.

The in vitro activities of azithromycin, clarithromycin and sparfloxacin were evaluated by studying inhibition of in vitro Chlamydia trachomatis propagation in McCoy cells, comparatively with erythromycin, ofloxacin and tetracycline. Fifteen clinical isolates of C. trachomatis were tested with an inoculum of 5.10(3) inclusion--forming units in a 96--well microtiter plate. Minimal inhibitory concentration (MIC) ranges were as follows: azithromycin, 0.06 to 0.125 microgram/ml; clarithromycin, 0.008 microgram/ml; erythromycin, 0.06 to 0.125 microgram/ml; ofloxacin 0.5 to 1 microgram/mg; sparfloxacin, 0.03 to 0.06 microgram/ml; and tetracycline 0.125 to 0.25 microgram/ml. Minimal bactericidal concentration (MBC) ranges, calculated from passage into antibiotic--free medium, were as follows: azithromycin 0.25 to 0.5 microgram/ml; clarithromycin, 0.03 to 0.125 microgram/ml; erythromycin, 0.25 to 2 micrograms/ml; ofloxacin, 0.5 to 1 microgram ml; sparfloxacin, 0.03-0.06 microgram/ml; and tetracycline, 1 to 4 micrograms/ml. Clarithromycin and sparfloxacin showed the greatest activity and clinical studies of these agents in C. trachomatis infections are therefore indicated.