Assessment of the in vitro and in vivo activity of ciprofloxacin measured against current standards of therapy.

The bactericidal activity of ciprofloxacin in active human serum was investigated using serum-resistant Escherichia coli C14 and Pseudomonas aeruginosa 220 as test organisms. In 100% or 80% human serum the growth rate of E. coli C14 was lower than in broth. This also influenced the killing rate of ciprofloxacin. Ciprofloxacin was more active in serum than norfloxacin or ofloxacin and killed Pseudomonas aeruginosa 220 much more rapidly than azlocillin or tobramycin. Rapid killing was also observed in vivo in the blood of intraperitoneally infected mice, ciprofloxacin being superior to norfloxacin, ofloxacin and sisomicin. In mouse protection studies with E. coli Neumann as infecting organism, the dose-effect ratio showed that, despite extremely low blood concentrations, ciprofloxacin had a full therapeutic effect at a dose of 2.5 mg/kg p.o. or less than or equal to 0.5 mg/kg s.c., whereas cefotaxime, despite similar low MIC values in vitro, had to be administered at a dose of 20 mg/kg s.c. in order to achieve 100% survival. These data indicate that ciprofloxacin is effective at low concentrations both in vitro and in vivo.