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Antimicrobial Agents and Chemotherapy

Year: 2008  |  Volume: 52  |  Issue: 11  |  Page No.: 3973 - 3979

Is 60 Days of Ciprofloxacin Administration Necessary for Postexposure Prophylaxis for Bacillus anthracis?

G. L. Drusano, Olanrewaju O. Okusanya, Adedoyin Okusanya, Brian Van Scoy, D. L. Brown, Robert Kulawy, Fritz Sorgel, Henry S. Heine and Arnold Louie


Sixty days of ciprofloxacin administration at 500 mg every 12 h is currently recommended for the prophylaxis of inhalational exposure to Bacillus anthracis. We examined Bacillus anthracis (Δ-Sterne strain) in our hollow-fiber infection model. We measured the ciprofloxacin concentrations achieved and the number of organisms present before heat shock (total population) and after heat shock (spore population). We fit a mathematical model to these data. Monte Carlo simulation with differing initial spore burdens (3, 5, and 6.9 log10 CFU/ml) demonstrated that 35 days of this regimen would completely clear the spore burden in 95% of patients. Durations of 110 days did not achieve 99.9% eradication, irrespective of initial burden, because of between-patient variance in drug pharmacokinetics. Given the absence of person-to-person transmission for Bacillus anthracis, adverse drug effects with long-term ciprofloxacin administration, and the possibility of engendering resistance in bodily flora, shorter prophylaxis duration should be given consideration, along with careful monitoring of all exposed individuals.

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