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 × 10⁶ 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.