In vitro studies of fleroxacin (Ro 23-6240), a new trifluorinated quinolone derivative.

The in vitro activity of fleroxacin (Ro 23-6240) against 441 bacterial isolates was compared with those of ciprofloxacin, ofloxacin, amoxycillin, cefadroxil, cefuroxime and tobramycin. An agar dilution method was used for the determination of minimal inhibitory concentrations (MICs). Ciprofloxacin showed the highest activity against the Enterobacteriaceae, 95% of the isolates were inhibited by 0.06 mg/l, but fleroxacin and ofloxacin were also highly active (MIC 90% = 0.5 and 0.25 mg/l, respectively). Ciprofloxacin was the most active agent against Pseudomonas aeruginosa (MIC 90% = 0.12 mg/l), whereas the activities of fleroxacin and ofloxacin were more variable. Tobramycin was highly active against P. aeruginosa, 75% of the isolates were inhibited by 0.5 mg/l or less. The quinolones and tobramycin exhibited high activity against Acinetobacter calcoaceticus, the great majority of the isolates being susceptible to 0.5 mg/l or less of any agent. All the quinolones showed high activity against Staphylococcus aureus, but fleroxacin was less active against Staphylococcus epidermidis and Staphylococcus saprophyticus than were the other derivatives. The pneumococcal and streptococcal isolates were markedly less susceptible to fleroxacin than to the other quinolones tested (MIC range 4-32 mg/l). All isolates of Haemophilus influenzae and Neisseria gonorrhoeae were inhibited by the lowest concentration of the quinolones employed in the study (0.03 mg/l). Cefuroxime was also highly active against N. gonorrhoeae, whether the strains were beta-lactamase-producing or not, but was somewhat less active against H. influenzae. The quinolones displayed moderate and similar activity against Bacteroides fragilis isolates (MIC range 1-16 mg/l). The MICs of fleroxacin against gram-negative rods were generally 4-16 times higher at pH 8.8 than those obtained at pH 5.8 and 7.3. The activity against gram-positive cocci was not markedly influenced by changes in pH.