Bactericidal activity of lomefloxacin SC 47111 (NY-198) and ciprofloxacin against selected pathogens

The bactericidal activity of lomefloxacin and ciprofloxacin against selected pathogens was compared using kill-kinetic methods to assess inhibitory (1 × MIC) and suprainhibitory (4 × MIC) concentrations. Five strains each of the following microorganisms were studied: Streptococcus pneumoniae, Streptococcus pyogenes, Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. We found that lomefloxacin was 8- to 16-fold less active than ciprofloxacin as measured by MICs. However, the bactericidal activities of both lomefloxacin and ciprofloxacin were comparable when concentrations × MIC and 4 × MIC were tested. For many of the isolates tested, such concentrations would be achieved clinically. The low MICs seen for the Gramnegative bacilli did not correlate with killing ability for either drug: concentrations 8–16 × MIC were needed for 99.9% killing of the final inoculum. Although higher concentrations of lomefloxacin are needed for inhibitory and bactericidal activity, the improved pharmacokinetics of lomefloxacin may result in this agent being comparable to ciprofloxacin.