In vitro evaluation of Ro 23-6240, a new fluorinated 4-quinolone

The in vitro antibacterial activity of Ro 23-6240 was assessed and compared with those of ciprofloxacin and beta-lactam antibiotics including several oral compounds against members of the family Enterobacteriaceae (n = 130) and Pseudomonas spp. (n = 31). In general, Ro 23-6240 was 2 dilution steps less active than ciprofloxacin. For the Pseudomonas spp. the MICs for 90% inhibition were 2 and 0.5 mg/1 for Ro 23-6240 and ciprofloxacin, respectively. For the other species tested, the MIC90 values for Ro 23-6240 ranged from 0.031 to 1 mg/1 and for ciprofloxacin from 0.016 to 0.25 mg/1. Spontaneous Ro 23-6240-resistant mutants were only isolated from Enterobacter cloacae with a frequency similar to that of ciprofloxacin (4.8 X 10(-8) and 2.4 X 10(-8), respectively). No resistant mutants were isolated from Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae and Pseudomonas aeruginosa at concentrations of 4 and 8 times the MIC of Ro 23-6240 or ciprofloxacin (frequency less than 10(-9).