In Vitro and in Vivo Antibacterial Activities of CS-940, a New 6-fluoro-8-difluoromethoxy Quinolone

The in vitro and in vivo activities of CS-940, a new 6-fluoro-8-difluoromethoxy quinolone, were compared with those of ciprofloxacin, tosufloxacin, sparfloxacin, and levofloxacin. The in vitro activity of CS-940 against gram-positive bacteria was nearly equal to or greater than those of the other quinolones tested. In particular, CS-940 was two to eight times more active against methicillin-resistant Staphylococcus aureus than the other quinolones, at the MIC at which 90% of the clinical isolates are inhibited. Against gram-negative bacteria, the activity of CS-940 was comparable to or greater than those of tosufloxacin, sparfloxacin, and levofloxacin, while it was lower than that of ciprofloxacin. The activity of CS-940 was largely unaffected by medium, inoculum size, or the addition of horse serum, but it was decreased under acidic conditions, as was also seen with the other quinolones tested. CS-940 showed potent bactericidal activity against S. aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. In oral treatment of mouse systemic infections caused by S. aureus, Streptococcus pneumoniae, Streptococcus pyogenes, E. coli, K. pneumoniae, Serratia marcescens, and P. aeruginosa, CS-940 was more effective than ciprofloxacin, sparfloxacin, and levofloxacin against all strains tested. Against experimental pneumonia with K. pneumoniae in mice, CS-940 was the most effective of all the quinolones tested. These results suggest that CS-940 may be effective in the therapy of various bacterial infections.