Abstract:

AIM: To evaluate the in vitro antibacterial efficacy of three quinolones—nemonoxacin, levofloxacin, and moxifloxacin—against Gram-positive (G⁺) and Gram-negative (G^?) bacteria, providing a scientific basis for rational clinical use. METHODS: Drug susceptibility tests were conducted on 292 clinical isolates (including Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecium, Corynebacterium striatum, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii) using the broth microdilution method to compare the distribution of minimum inhibitory concentrations (MICs) and pharmacodynamic characteristics. The mutant prevention concentration (MPC) of selected strains was further determined by the agar dilution method to evaluate their mutant prevention capabilities. RESULTS: For G⁺ bacteria, nemonoxacin exhibited superior activity against Staphylococcus aureus (MIC₉₀=16 μg/mL), Staphylococcus epidermidis (MIC₉₀=2 μg/mL), and Corynebacterium striatum (MIC₉₀=4 μg/mL) compared to levofloxacin and moxifloxacin. In MRSA strains, the susceptibility rate of nemonoxacin reached 66.96%. For G^? bacteria, the MIC₉₀ of levofloxacin against P. aeruginosa was 2 μg/mL, which was lower than that of nemonoxacin and moxifloxacin (both 4 μg/mL). For K. pneumoniae, E. coli, and A. baumannii, the MIC₉₀ values for all three drugs were mostly 64 μg/mL, indicating overall low susceptibility. In terms of mutant prevention, nemonoxacin showed an MPC₉₀ of 2 μg/mL in MSSA, which was lower than that of moxifloxacin (4 μg/mL) and levofloxacin (16 μg/mL), with the narrowest range of selection index (SI). In resistant G^— bacteria, the MPC₉₀ and SI values for all three drugs were generally higher. However, the MPC₉₀ of levofloxacin against resistant P. aeruginosa (16 μg/mL) was lower than that of moxifloxacin (32 μg/mL) and nemonoxacin (64 μg/mL). CONCLUSION: Nemonoxacin demonstrates stronger antibacterial activity against G⁺ bacteria such as S. aureus (including MRSA) and possesses the most potent mutant prevention capability in MSSA. Levofloxacin maintains favorable antibacterial activity against P. aeruginosa, and its MPC is relatively lower among the tested drugs. Clinical selection should be based on the specific pathogen type and the risk of resistance.

Key words: nemonoxacin, levofloxacin, moxifloxacin, minimum inhibitory concentration, mutant prevention concentration