Doxycycline or ciprofloxacin prophylaxis and therapy against experimental Yersinia pestis infection in mice

Abstract

The efficacy of doxycycline and ciprofloxacin against an experimental plague infection was assessed by comparing the median lethal dose (MLD) of Yersinia pestis in antibiotic-treated and untreated mice. The MLD of Y, pestis GB strain in untreated mice by the intra-peritoneal route was 23 cfu. If ciprofloxacin dosage (20 or 40 mg/kg twice daily) was initiated 48 h before infection, it afforded complete protection against an intra-peritoneal challenge of 5.24 x 107 cfu. Ciprofloxacin therapy initiated 24 h post-challenge was less protective, the MLD was raised to 2.0 x 105 and 2.2 x 105 cfu for 40 and 20 mg/kg respectively. Doxycycline dosage (40 mg/kg twice daily) initiated 48 h prior to infection raised the MLD to 1.6 x 104 cfu, but other prophylactic and therapeutic regimes were ineffective against challenges greater than 6.76 x 102 cfu. Ciprofloxacin may therefore be a useful antibiotic to consider for the treatment of plague.