Post-exposure prophylaxis of systemic anthrax in mice and treatment with fluoroquinolones

Objectives: To compare the fluoroquinolones gatifloxacin and moxifloxacin with ciprofloxacin for post-exposure prophylaxis of systemic anthrax in a BALB/c mouse model. Methods: Treated mice and controls were inoculated subcutaneously with 5×104 spores/mouse of Bacillus anthracis Ames strain and observed for 37 days after challenge. Treated mice were given 100 mg/kg of antibiotic orally twice daily for 14 days, starting at various times post-challenge. Results: Treatment starting 6 h post-challenge resulted in survival rates of 90%, 15% and 40% for gatifloxacin, moxifloxacin and ciprofloxacin, respectively. Treatment commencing 24 h post-challenge resulted in survival rates of 65%, 10% and 5%, respectively. Treatment starting more than 24 h after exposure had little effect on survival. Conclusions: Gatifloxacin appeared to be more effective than moxifloxacin or ciprofloxacin, at similar doses, for early post-exposure treatment of murine systemic anthrax. However, these results might be due to differences in potency or pharmacokinetic properties.