In vivo protection against intranasal virulent anthrax challenge. Percent survival of female Swiss Webster mice, 10 per group, infected with 5 LD50 B. anthracis Ames spores by intranasal inoculation. Control mice were treated with saline 1 h post spore challenge via intraperitoneal injection. All mice were monitored twice dailyfor signs of illness or death. A. Mice were treated with 32 mg/kg anti-PA83 IgG 24 h post spore challenge via intraperitoneal injection. P = 0.0161 by thelogrank test. B. Mice were treated with Ciprofloxacin alone or in combination with anti-PA83 IgG at 32 mg/kg (24 h post spore challenge). Ciprofloxacin was administered twice daily at 0.9 mg/day via intraperitonealinjection for the first six days post spore challenge. Statistical significance using the logrank test as follows: Anti-PA83 IgG P = 0.0161, Anti-PA83 IgG + Ciprofloaxcin P = 0.0007 and Ciprofloaxcin P = 0.0156.