In vitro activity of Bay y 3118, a new quinolone

MICs of Bay y 3118, ciprofloxacin, ofloxacin, clarithromycin, azithromycin, cefuroxime, amoxicillin-clavulanate, and trimethoprim-sulfamethoxazole for 878 recent clinical isolates were determined by broth microdilution methods. Among the three quinolones, Bay y 3118 was the most active against Haemophilus influenzae, Moraxella catarrhalis, Acinetobacter baumannii, Xanthomonas maltophilia, gram-positive cocci, and anaerobes; MICs for 50% of the strains (MIC50s) and MIC90s were < or = 0.015 and < or = 0.015, < or = 0.015 and < or = 0.015, 0.03 and 2, 0.25 and 0.5, 0.06 and 1, and 0.12 and 0.25 micrograms/ml, respectively. For gram-positive cocci and anaerobes, these values were 16- to 32-fold (4 to 5 log2 dilution steps) lower than those for ciprofloxacin and ofloxacin. Bay y 3118 was similar in activity to ciprofloxacin and more active than ofloxacin against members of the family Enterobacteriaceae and Pseudomonas aeruginosa; Bay y 3118 MIC50s and MIC90s were 0.03 and 0.25 and 0.5 and 8 micrograms/ml, respectively. Scattergrams and regression analyses comparing quinolone MICs indicated that, despite differences in activity, organisms relatively susceptible to one were relatively susceptible to all and organisms relatively resistant to one were relatively resistant to all. However, the greater in vitro activity of Bay y 3118 was most pronounced against relatively resistant organisms. Pending pharmacokinetic and safety data for Bay y 3118, there is reasonable anticipation that its enhanced activity against gram-positive cocci and anaerobes would broaden the clinical utility of the quinolone class of antimicrobial agents.