In vitro activity of ciprofloxacin, norfloxacin and nalidixic acid

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Abstract
The in vitro antibacterial activity of the new quinoline derivative ciprofloxacin (BAY 0 9867) was evaluated in comparison to norfloxacin and nalidixic acid using 495 clinical strains of gram-negative and gram-positive bacteria. The compound was highly active againstEnterobacteriaceae, with MICs ranging from 0.008 mg/l to 4 mg/l, whereas the MICs of norfloxacin ranged from 0.03 mg/l to 16 mg/l. All strains ofPseudomonas aeruginosa andAcinetobacter calcoaceticus were inhibited with a concentration of 2 mg/l ciprofloxacin and 32 mg/l norfloxacin. Ciprofloxacin was also active against gram-positive cocci. The MICs forStaphylococcusaureus, Staphylococcus epidermidis, andStreptococcus faecalis ranged from 0.008 to 2.0 mg/l. The activity of ciprofloxacin was only slightly influenced by inoculum size, whereas an acid environment caused a noticeable decrease in the activity. Ciprofloxacin would seem to be a promising antibacterial agent for the treatment of urinary tract infection.