In vitro activity of CP-74,667. A new fluoroquinolone compared with other quinolones

CP-74,667, a 6-fluoro-7-bridged piperazinyl-1-cyclopropyl-4 quinolone, inhibited 90% of staphylococci, beta-hemolytic streptococci, enterococci, Enterobacteriaceae, and Pseudomonas aeruginosa at less than or equal to 2 micrograms/ml. Ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus had minimum inhibitory concentration (MIC50) of 4 micrograms/ml and an MIC90 of 8 micrograms/ml. CP-74,667 was fourfold more active than ciprofloxacin against Streptococcus pneumoniae and St. pyogenes, but equal or less active than tosufloxacin against Gram-positive species. The MIC90 for P. aeruginosa was 5 micrograms/ml similar to temafloxacin. The CP-74,667 MIC90 for Bacteroides fragilis was 2 micrograms/ml, equal to tosufloxacin and temafloxacin. Activity was eight- to 16-fold less at pH 5.5 compared with pH 7.4 and also eight- to 16-fold less in urine. Magnesium ions markedly increased the CP-74,667 minimum bactericidal concentrations (MBCs). The development of resistance to CP-74,667 was similar to that found for other fluoroquinolones.