In vitro activity of the new 4-quinolone compound Ro 23-6240

The in vitro activity of the new 4-quinolone Ro 23-6240 was compared with that of pefloxacin, ciprofloxacin, norfloxacin, nalidixic acid and gentamicin against a total of 397 recent clinical isolates. An agar dilution procedure was used to determine MICs and two inocula (10(4) and 10(6) CFU) were used throughout. Ro 23-6240 inhibited most species of the Enterobacteriaceae, Haemophilus influenzae and Staphylococcus aureus (including methicillin-resistant strains) at less than or equal to 1 mg/l. Pseudomonas aeruginosa was somewhat more resistant (MIC 90 4 mg/l) and the Bacteroides fragilis group were considerably more resistant (MIC 90 32 mg/l). Overall Ro 23-6240 was as active as pefloxacin but was two- to eight-fold less active than ciprofloxacin against most species tested.