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 (MIC 90, 0.5 μg/ml) with activity comparable to that of ofloxacin (MIC 90, 0.25 μg/ml). Lomefloxacin was moderately active against isolates of Pseudomonas aeruginosa (MIC 90, 4 μg/ml), and again the activity was comparable to ofloxacin (MIC 90, 4 μg/ml) but was eightfold less than ciprofloxacin (MIC 90, 0.5 μg/ml). Lomefloxacin was also active against isolates of Staphylococcus aureus (MIC 90, 1 μg/ml), irrespective of methicillin susceptibility, and this activity was most comparable to ofloxacin (MIC 90, 0.5 μg/ml) and ciprofloxacin (MIC 90, 0.5 μg/ml). Lomefloxacin was fourfold less active than either ofloxacin or ciprofloxacin against isolates of Enterococcus faecalis (MIC 90, 8 μg/ml) and Streptococcus pneumoniae (MIC 90, 8 μg/ml). In common with ofloxacin and ciprofloxacin, lomefloxacin was very active against isolates of Neisseria spp. (MIC 90, ⩽0.06 μg/ml), Haemophilus spp. (MIC 90, ⩽0.06 μg/ml), Legionella spp. (MIC 90, ⩽0.06 μg/ml), Vibrio spp. (MIC 90, ⩽0.06 μg/ml), and Campylobacter jejuni (MIC 90, 1 μg/ml). Lomefloxacin showed poor activity against isolates of Bacteroides spp. (MIC 90, 16 μg/ml) or Clostridium difficile MIC 90, 32 μg/ml) and was only moderately active against isolates of Clostridium perfringens (MIC 90, 2 μg/ml), Peptostreptococcus spp. (MIC 90, 4 μg/ml), Chlamydia trachomatis (MIC 90, 4 μg/ml), Mycoplasma hominis (MIC 90, 2 μg/ml), and Ureaplasma urealyticum (MIC 90, 8 μg/ml). Lomefloxacin was found to be bactericidal at concentrations generally close to the MIC with 〉3 log 10 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.