In vitro activity of the aryl-fluoroquinolones A-56619 and A-56620 and evaluation of disk susceptibility tests.

The activity of two new quinolones, A-56619 and A-56620, was compared in vitro to that of norfloxacin and ciprofloxacin against 6,699 bacterial isolates in four separate clinical laboratories. The overall percentage of strains susceptible to designated concentrations were as follows: 99.1% for norfloxacin (MIC less than or equal to 4.0 micrograms/ml), 96.1% for ciprofloxacin (MIC less than or equal to 1.0 micrograms/ml), 96.8% for A-56620 (MIC less than or equal to 2.0 micrograms/ml) and 96.1% for A-56619 (MIC less than or equal to 4.0 micrograms/ml). For disk diffusion susceptibility tests 10 micrograms A-56619 disks are tentatively recommended with interpretive standards of greater than or equal to 18 mm for susceptibility and less than or equal to 13 mm for resistance; 5 micrograms A-56620 disks may be used with tentative standards of greater than or equal to 19 mm for susceptibility and less than or equal to 14 mm for resistance.