Abstract
The in vitro activity of pazufloxacin (PZFX), a new fluoroquinolone, was compared with those of ofloxacin (OFLX), norfloxacin (NFLX), ciprofloxacin (CPFX) and levofloxacin (LVFX). The MIC90 of PZFX against methicillin-susceptible and methicillin-resistant Staphylococcus aureus were 0.39 and 12.5μg/ml, better than those of the other reference fluoroquinolones. Some isolates of CPFX-resistant S. aureus (MIC of CPFX, ≥3.13μg/ml) were still susceptible to PZFX (MIC of PZFX, ≤0.39μg/ml). The MIC90s of PZFX against Enterobacteriaceae (except Serratia marcescens) were 0.024 to 0.39μg/ml, and against S. marcescens and Pseudomonas aeruginosa were 6.25 and 3.13μg/ml, which they were comparable to CPFX and better than those of the other reference quinolones. The activity of PZFX against anaerobes was comparable to those of CPFX and LVFX, and better than those of OFLX and NFLX. The MBCs of PZFX were either equal to or two-fold higher than the MICs. At a concentration of four times the MIC, the frequencies of appearance of spontaneous mutants resistant to PZFX against S. aureus, Escherichia coli, S. marcescens and P. aeruginosa were 2.3 × 10-8 to < 1.2 ×10-9 The 50% inhibitory concentrations of PZFX for DNA gyrases isolated from S. aureus, E. coli and P. aeruginosa were 32, 0.88 and 14μg/ml, respectively.
PZFX had a broad spectrum of activity and had potent activity against Gram-positive and-negative bacteria. Its activity was bactericidal, and its mechanism of action was the inhibition of the supercoiling activity of bacterial DNA gyrase.
