In vivo efficacy of fluoroquinolones against systemic tularaemia infection in mice.

OBJECTIVES The in vivo efficacy of ciprofloxacin, gatifloxacin and moxifloxacin were assessed in an experimental Francisella tularensis Schu S4 infection in the BALB/c mouse model. METHODS Mice were given 100 mg/kg of antibiotic by oral administration twice daily commencing at 6, 24 or 48 h post-exposure and continued for 14 days post-exposure. All mice were challenged subcutaneously with 1 x 10(6) cfu F. tularensis Schu S4 and observed for a period of 56 days. RESULTS Treatment initiated 6 h post-exposure resulted in 94, 100 and 100% survival for ciprofloxacin, gatifloxacin and moxifloxacin, respectively. When treatment was delayed until 24 h post-exposure the survival rates were ciprofloxacin 67%, gatifloxacin 96% and moxifloxacin 100%. Treatment initiated at 48 h post-exposure resulted in a significant reduction in the survival rate of the ciprofloxacin-treated mice, with 0% survival compared with 84 and 62% for gatifloxacin and moxifloxacin, respectively. Non-treated infected control mice died within 96 h post-exposure. Dexamethasone given at day 42 for 7 days to suppress the animals' immune system caused relapse in all of the treatment groups. CONCLUSIONS Both gatifloxacin and moxifloxacin were more effective at preventing mortality than ciprofloxacin and could be considered as alternative antibiotics in the treatment of systemic F. tularensis infection.