Comparative activities of ciprofloxacin (Bay o 9867), norfloxacin, pipemidic acid, and nalidixic acid.

An agar dilution method was used to measure the minimal inhibitory concentrations of ciprofloxacin (Bay o 9867), norfloxacin, pipemidic acid, and nalidixic acid against 496 clinical isolates. Ciprofloxacin and norfloxacin were active against all species tested (90% minimal inhibitory concentrations less than or equal to 8 micrograms/ml), although ciprofloxacin was somewhat more active, e.g., against gram-positive cocci. Pipemidic acid and nalidixic acid were active against most of the members of the Enterobacteriaceae, but Klebsiella species and Providencia stuartii were only inhibited by a high concentration of nalidixic acid.