Comparative in vitro activity of lomefloxacin, a difluoro-quinolone

Lomefloxacin is a new difluoro-quinolone. In this study, we have determined the in vitro activity of lomefloxacin against a wide range of clinical bacterial isolates and compared it with that of other fluoro-quinolones and some unrelated antimicrobials. Lomefloxacin was very active against Enterobacteriaceae (MIC90, 0.5 micrograms/ml) with activity comparable to that of ofloxacin (MIC90, 0.25 micrograms/ml). Lomefloxacin was moderately active against isolates of Pseudomonas aeruginosa (MIC90, 4 micrograms/ml), and again the activity was comparable to ofloxacin (MIC90, 4 micrograms/ml) but was eightfold less than ciprofloxacin (MIC90, 0.5 micrograms/ml). Lomefloxacin was also active against isolates of Staphylococcus aureus (MIC90, 1 micrograms/ml), irrespective of methicillin susceptibility, and this activity was most comparable to ofloxacin (MIC90, 0.5 micrograms/ml) and ciprofloxacin (MIC90, 0.5 micrograms/ml). Lomefloxacin was fourfold less active than either ofloxacin or ciprofloxacin against isolates of Enterococcus faecalis (MIC90, 8 micrograms/ml) and Streptococcus pneumoniae (MIC90, 8 micrograms/ml). In common with ofloxacin and ciprofloxacin, lomefloxacin was very active against isolates of Neisseria spp. (MIC90, less than or equal to 0.06 micrograms/ml), Haemophilus spp. (MIC90, less than or equal to 0.06 micrograms/ml), Legionella spp. (MIC90, less than or equal to 0.06 micrograms/ml), Vibrio spp. (MIC90, less than or equal to 0.06 micrograms/ml), and Campylobacter jejuni (MIC90, 1 microgram/ml). Lomefloxacin showed poor activity against isolates of Bacteroides spp. (MIC90, 16 micrograms/ml) or Clostridium difficile MIC90, 32 micrograms/ml) and was only moderately active against isolates of Clostridium perfringens (MIC90, 2 micrograms/ml), Peptostreptococcus spp. (MIC90, 4 micrograms/ml), Chlamydia trachomatis (MIC90, 4 micrograms/ml), Mycoplasma hominis (MIC90, 2 micrograms/ml), and Urea-plasma urealyticum (MIC90, 8 micrograms/ml). Lomefloxacin was found to be bactericidal at concentrations generally close to the MIC with greater than 3 log10 reduction in viability of exponentially dividing cultures of Escherichia coli and S. aureus within 5 hr of exposure to concentrations at eight times the MIC. These results indicate a potential clinical role for lomefloxacin in the treatment of genitourinary tract infections caused by Gram-positive and Gram-negative bacteria, respiratory tract infections caused by susceptible organisms, and soft tissue infections caused by S. aureus.