Antibacterial activities of ciprofloxacin, norfloxacin, oxolinic acid, cinoxacin, and nalidixic acid

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Abstract
In vitro studies were performed comparing ciprofloxacin (Bay o 9867) and norfloxacin with 3 related organic acids. Ciprofloxacin was 2-8 times more active than norfloxacin 658 bacterial isolates representing 30 spp. For all species tested, ciprofloxacin minimum inhibitory concentrations for 90% inhibition were .ltoreq. 2.0 .mu.g/ml. Additional tests with 5994 isolates detected only 37 (0.6%) strains resistant to 2.0 .mu.g of ciprofloxacin/ml and 106 (1.8%) resistant to 1.0 .mu.g/ml; 6 (0.1%) of the 5994 strains were resistant to 16 .mu.g of norfloxacin/ml; 129 (2.1%) were resistant to 4.0 .mu.g/ml. The majority of resistant strains were streptococci or Pseudomonas spp. Resistance among the Enterobacteriaceae was extremely rare (i.e., > 99.8% susceptible to both drugs).