In vitro activities of ciprofloxacin, norfloxacin, pipemidic acid, cinoxacin, and nalidixic acid against Chlamydia trachomatis

The in vitro activities of five quinolinecarboxylic acids against two laboratory strains of Chlamydia trachomatis were compared. The minimal inhibitory concentrations of nalidixic acid, cinoxacin, and pipemidic acid were all greater than or equal to 50 micrograms/ml; the activity of norfloxacin was intermediate (minimal inhibitory concentration, 8 to 16 micrograms/ml). Ciprofloxacin was the most active of these drugs (minimal inhibitory concentration, 0.5 to 1 microgram/ml).