The efficacy of
ciprofloxacin (Bay o 9867), a promising new
quinolone, was compared with the efficacy of
azlocillin plus
tobramycin in rabbits with experimentally induced Pseudomonas aeruginosa
endocarditis. The MBCs of
ciprofloxacin,
azlocillin, and
tobramycin against the test strain were 0.5, 8, and 4 micrograms/ml respectively.
Ciprofloxacin at a concentration of 50 mg/kg or
azlocillin at a concentration of 200 mg/kg in combination with
tobramycin at a concentration of 5 mg/kg was administered intramuscularly at 8-h intervals for 4 days. Both regimens produced median peak serum bactericidal titers of 1:8. The concentrations of
ciprofloxacin,
azlocillin, and
tobramycin in serum, 1.8 +/- 0.7, 154 +/- 48, and 9.1 +/- 2.4 micrograms/ml (mean +/- standard deviation), respectively, closely approximated concentrations found in humans after accepted dosages. At the end of treatment, the titers of P. aeruginosa were 3.0 +/- 1.6 log10 CFU/g of vegetation (mean +/- standard deviation) for recipients of
ciprofloxacin and 3.2 +/- 1.3 log10 CFU/g of vegetation for recipients of
azlocillin plus
tobramycin. These values compared with control titers of 7.3 +/- 1.6 CFU/g. These data indicate that at the doses used,
ciprofloxacin was as effective as
azlocillin plus
tobramycin in the treatment of P. aeruginosa
endocarditis in rabbits. Since the latter
drug combination has proven efficacy,
ciprofloxacin deserves further evaluation in the
therapy of systemic
infections in animal models and in humans.