In vitro activity of RO 23-6240 (AM-833): a new fluoroquinolone.

The in vitro activities of RO 23-6240 (AM-833) and four comparative fluoroquinolones were studied. Minimal inhibitory concentrations (MICs) of RO 23-6240, which inhibited at least 90% of strains, were less than or equal to 0.03-1 microgram/ml for Staphylococcus aureus, Staphylococcus epidermidis, Enterobacteriaceae, Acinetobacter anitratus Aeromonas hydrophila, Branhamella catarrhalis, and Haemophilus influenzae, 2-8 micrograms/ml for Staphylococcus saprophyticus, streptococci, diphtheroids, and Pseudomonas spp., and 1-32 micrograms/ml for anaerobic species. MICs of ofloxacin, pefloxacin, norfloxacin, and ciprofloxacin paralleled those of RO 23-6240. With all five drugs, MICs were minimally affected by inoculum size and minimal bacterial concentrations (MBCs) were always within two dilution steps (log2) of MICs.