Comparative activity of the 4-quinolones.

Minimal inhibitory concentrations (MICs) of the 4-quinolones ciprofloxacin, enoxacin, norfloxacin, ofloxacin, pefloxacin, difloxacin, A-56620, and CI-934 are consistent world-wide, with allowances for differences in acquired resistance. MICs of these drugs for Enterobacteriaceae correlate with those of nalidixic acid, but resistance to the quinolones is rare if a breakpoint of greater than 2 mg/L is accepted. Most intestinal pathogens are sensitive. Acinetobacter, Pseudomonas aeruginosa, and other Pseudomonas species except Pseudomonas maltophilia are usually sensitive. Ciprofloxacin is generally the most active of the 4-quinolones against these organisms. All of the new agents have antistaphylococcal activity, but that of norfloxacin and ofloxacin is borderline. Against streptococci, including enterococci and pneumococci, the drugs' activity is moderate or poor. Haemophilus influenzae and Branhamella catarrhalis are very sensitive. Gonococci and meningococci are also highly sensitive to the new agents, but activity against Chlamydia trachomatis and the mycoplasmas is borderline. The organisms associated with nonspecific vaginal infection are not very sensitive. Anaerobes except Bacteroides ureolyticus and Clostridium perfringens are mostly resistant.