The in-vitro activity of PD127,391, a new quinolone.

MICs of PD127,391 a new 4-quinolone, and of CI934 and ciprofloxacin, two previously reported 4-quinolones, were determined for common clinical bacterial isolates by an agar-dilution method. PD127,391 was the most active drug against Enterobacteriaceae and Acinetobacter spp (MICs less than 0.12 mg/l) and as active as ciprofloxacin against Aeromonas spp. (MICs less than 0.008 mg/l) and Pseudomonas aeruginosa (MICs less than 1 mg/l). It was more active than ciprofloxacin against Pseudomonas spp. including Ps. maltophilia (MICs less than 0.25 mg/l). All three drugs had high activity, with PD129,391 again the best, against Haemophilus influenzae Brahmamella catarrhalis, and Neisseria gonorrhoeae. PD127,391 was much more active than the other drugs against Campylobacter coli/jejuni (PD127,391 MICs less than 0.03 mg/l) and Gardnerella vaginalis (PD127,391 MICs less than 0.25 mg/l). PD127,391 inhibited all staphylococci at less than 0.06 mg/l and streptococci at less than 0.5 mg/l, thus being more active than CI934 or ciprofloxacin. PD127,391 was much more active against anaerobic cocci, Bacteroides spp. and clostridia (including Clostridium difficile) (MICs less than 1 mg/l) than was CI934 (MICs less than 16 mg/l) or ciprofloxacin (MICs less than 64 mg/l). No bacterium that we examined required more than 1 mg/l of PD127,391 for inhibition, and there was no cross resistance with unrelated antibiotics.