A multicenter comparative study of the in vitro activity of fleroxacin and other antimicrobial agents

The in vitro activity of fleroxacin was determined by broth microdilution against 2,079 recent bacterial isolates and compared to the activities of ciprofloxacin, ofloxacin, lomefloxacin, cefaclor, cefuroxime, cefixime, ceftriaxone, amoxicillin/clavulanate, trimethoprim/sulfamethoxazole (TMP-SMX), and, as appropriate, erythromycin and oxacillin. Most Enterobacteriaceae were inhibited by the quinolones at a concentration of < or = 1 microgram/ml; MIC90s of fleroxacin, ciprofloxacin, ofloxacin, and lomefloxacin were 0.25, 0.5, 1 and 1 micrograms/ml, respectively. Fleroxacin was 2-fold more active than ciprofloxacin against Providencia stuartii and Serratia marcescens. Aside from the quinolones, ceftriaxone and TMP-SMX were the most active antibiotics against the Enterobacteriaceae, with MIC90s of 8 and 16 micrograms/ml, respectively. Ciprofloxacin was more active against Pseudomonas aeruginosa than the other quinolones, while fleroxacin was more active against Stenotrophomonas maltophilia: 17.7, 11.2, 20.0, and 22.4% of P. aeruginosa were resistant to fleroxacin, ciprofloxacin, ofloxacin, and lomefloxacin, respectively. Moraxella catarrhalis and Haemophilus influenzae were uniformally susceptible to all antibiotics tested, as were the majority of oxacillin-susceptible staphylococci. The MIC90s of the quinolones and of the beta-lactam antibiotics for oxacillin-resistant staphylococci were 8- to 256-fold higher than for oxacillin-susceptible staphylococci. The beta-lactam antibiotics, TMP-SMX, and erythromycin were more active than the quinolones against streptococci; all antibiotics were poorly active against enterococci. Fleroxacin is active against a broad range of gram-negative bacilli and against oxacillin-susceptible staphylococci and should prove useful for such infections. However, its use cannot be recommended for infections due to oxacillin-resistant staphylococci, streptococci, or enterococci.