In vitro activity of Ro 23-6240, a new difluoroquinolone derivative, compared with that of other antimicrobial agents.

Ro 23-6240 is a new difluorinated quinolone antimicrobial agent. Its in vitro activity against a wide range of bacteria was compared with those of other quinolones and beta-lactams. Generally, members of the family Enterobacteriaceae were inhibited by low concentrations of Ro 23-6240 (MIC90 [MIC for 90% of isolates tested], less than or equal to 1 microgram/ml). Ninety percent of Staphylococcus aureus (including methicillin-resistant strains) and Neisseria gonorrhoeae isolates were inhibited by 0.5 microgram/ml. Pseudomonas aeruginosa (MIC90, 2 micrograms/ml) and Bacteroides fragilis (MIC90, 4 micrograms/ml) showed intermediate susceptibility, and Streptococcus pneumoniae (MIC90, 8 micrograms/ml) was less susceptible. Strains resistant to nalidixic acid were less susceptible to all the quinolones tested. The protein binding of Ro 23-6240 (5 micrograms/ml) was 27%.