Interpretive criteria for susceptibility testing of CI-960 (PD127391, AM-1091), fleroxacin, lomefloxacin, and temafloxacin against Neisseria gonorrhoeae, including drug stability in GC agar medium.

CI-960, fleroxacin, lomefloxacin, and temafloxacin were tested against over 100 strains of Neisseria gonorrhoeae. Each organism was tested in triplicate by using agar dilution and disk diffusion methods recommended by the National Committee for Clinical Laboratory Standards. CI-960 was the most potent compound, with a MIC against 90% of the strains tested of 0.008 microgram/ml, and the least active was fleroxacin (MIC against 90% of strains, 0.12 microgram/ml). Only the susceptible interpretive category was recommended for the CI-960 tests as follows: 5-micrograms disk, greater than or equal to 39 mm (MIC correlate, less than or equal to 0.12 microgram/ml). Three interpretive categories were proposed for the other fluoroquinolones as follows: fleroxacin, 5-micrograms disk susceptible at greater than or equal to 33 mm (MIC correlate, less than or equal to 0.25 microgram/ml), intermediate at 28 to 32 mm (MIC correlate, 0.5 microgram/ml), and resistant at less than or equal to 27 mm (MIC correlate, greater than 0.5 microgram/ml); lomefloxacin, 10-micrograms disk susceptible at greater than or equal to 35 mm (MIC correlate, less than or equal to 0.12 microgram/ml), intermediate at 28 to 34 mm (MIC correlates, 0.25 to 0.5 microgram/ml), and resistant at less than or equal to 27 mm (MIC correlate, greater than 0.5 microgram/ml); and temafloxacin, 5-micrograms disk susceptible at greater than or equal to 36 mm (MIC correlate, less than or equal to 0.06 microgram/ml), intermediate at 28 to 35 mm (MIC correlates 0.12 to 0.25 microgram/ml), and resistant at less than or equal to 27 mm (greater than 0.25 microgram/ml). Interpretive agreement between disk diffusion results and the MICs was 100% for each agent, with the exception of lomefloxacin, which had a 0.9% minor error. All drugs were stable in GC agar medium for at least 21 days when stored at 2 to 5 degrees C.