In vivo oral efficacy of levofloxacin for treatment of systemic Pseudomonas aeruginosa infections in a murine model of septicemia

The in vivo efficacies of levofloxacin and ciprofloxacin in lethal, systemic Pseudomonas aeruginosa infections in mice were compared. MICs of levofloxacin and ciprofloxacin ranged from 0.5 to 2.0 micrograms/ml and from 0.12 to 1.0 microgram/ml respectively. Infecting doses ranged from 5.0 x 10(1) to 3.2 x 10(3) CFU per mouse, depending on the isolate. Test fluoroquinolones were administered orally at 1 h (single dose) or at 1 and 3 h (divided dose) postinfection, with 10 infected mice used for each of six concentrations of each fluoroquinolone tested (1 to 40 mg/kg of body weight) in each dosing regimen. Whether given in a single or a divided dose, the total daily dose was the same for each fluoroquinolone. For mice treated 1 h postinfection with levofloxacin and ciprofloxacin, the effective doses for 50% of the infected mice ranged from 2.09 to 13.80 mg/kg and from 2.34 to 11.22 mg/kg, respectively, and for those treated 1 and 3 h postinfection, the effective doses for 50% of the infected mice ranged from 3.71 to 16.98 mg/kg and from 2.95 to 13.18 mg/kg, respectively. Although the potency varied for both levofloxacin and ciprofloxacin among all strains of P. aeruginosa tested, there were small differences within the same strain for levofloxacin and ciprofloxacin when given in the same dosing regimen. Levofloxacin proved nearly as effective as ciprofloxacin against a systemic P. aeruginosa infection in mice.