Fig. (5) A. Survival of Swiss-Webster mice treated with various doses of levofloxacin for six days starting 24 h after challenge with 5 LD50 of Y. pestis C092 cells by nasal instillation. The horizontal bar indicates the period of levofloxacin treatment. Complete protection against primary challenge was achieved by a dose of 5 mg/kg/day levofloxacin. Significance for all groups began at day 3, and while the two lowest doses were only significant for this time point, all other groups were significant until day 32. Significance from the control was determined by the Fisher Exact Test (p<0.05). B. Survival of Swiss-Webster mice challenged with Y. pestis C092 followed treatment with 5 or 10 mg/kg/day of Levofloxacin at various times post challenge. Animals were dosed for 6 days, once initiated, and survival was compared to the control group (no levofloxacin). Significance (p<0.05) for all treatment groups from the control group began at day 3. Both doses of levofloxacin at 24 and 36 h postchallenge were significantly different (p<0.05) from the control group until the end of the study, but at 48 h both 5 and 10mg/kg groups were not significantly different from the control group (p>0.05).