Efficacy of Doxycycline and Ciprofloxacin for Treatment of Pneumonic Tularemia in Cynomolgus Macaques.

Abstract

The incidence of pneumonic tularemia is very low; therefore, it is not feasible to conduct clinical efficacy testing of tularemia medical countermeasures (MCMs) in humans. The US Food and Drug Administration's Animal Model Qualification Program under the Drug Development Tools Program is a regulatory pathway for animal models used in MCM efficacy testing and approval under the Animal Rule. The National Institute of Allergy and Infectious Diseases and Biomedical Advanced Research and Development Authority worked together to qualify the cynomolgus macaque model of pneumonic tularemia. Using the model parameters and end points defined in the qualified model, efficacy of the antibiotics doxycycline and ciprofloxacin was evaluated in separate studies. Antibiotic administration, aimed to model approved human dosing, was initiated at time points of 24 hours or 48 hours after onset of fever as an indicator of disease. Upon aerosol exposure (target dose of 1000 colony-forming units) to Francisella tularensis SchuS4, 80% of vehicle-treated macaques succumbed or were euthanized. Ciprofloxacin treatment led to 10 of 10 animals surviving irrespective of treatment time. Doxycycline administered at 48 hours post-fever led to 10 of 10 animals surviving, while 9/10 animals survived in the group treated with doxycycline 24 hours after fever. Selected surviving animals in both the placebo and doxycycline 48-hour group showed residual live bacteria in peripheral tissues, while there were no bacteria in tissues from ciprofloxacin-treated macaques. Both doxycycline and ciprofloxacin were efficacious in treatment of pneumonic tularemia, although clearance of bacteria may be different between the 2 drugs.