In vitro activity of amifloxacin (WIN 49,375) compared with those of ciprofloxacin and ofloxacin.

The in vitro activity of the novel fluoroquinolone derivative, amifloxacin (WIN 49,375), was compared with the activities of ciprofloxacin and ofloxacin. A total of 500 clinical isolates of Gram-negative and Gram-positive bacteria were included, and the minimal inhibitory concentration (MIC) was determined by an agar dilution method. All drugs were highly active against Enterobacteriaceae, but ciprofloxacin showed the highest activity on a weight-for-weight basis (MIC 90% less than or equal to 0.03 mg/l). Ciprofloxacin was the most active agent against Pseudomonas isolates; all isolates being inhibited by 0.25 mg/l or less. The staphylococcal isolates were inhibited by ciprofloxacin and ofloxacin at relatively low concentrations (MIC 100% = 1 mg/l), whereas amifloxacin showed moderate activity against the majority of these isolates. Ciprofloxacin was highly active against enterococci, ofloxacin was moderately active, and amifloxacin was inactive. All Neisseria gonorrhoeae isolates were susceptible to the lowest concentrations of the agents that were employed in the study (0.03 mg/l).