Based on the pharmacokinetic-pharmacodynamic (PK-PD) parameters of ciprofloxacin in rhesus monkeys, the efficacies of levofloxacin, sparfloxacin, norfloxacin, and tosufloxacin against anthrax in humans were examined. The optimal PK-PD parameter for the prophylaxis or treatment of infection with Bacillus anthracis is not clearly defined. To evaluate the efficacy of fluoroquinolones against anthrax, PK-PD parameters and the protein-binding effect of fluoroquinolones are used. B. anthracis is very susceptible to fluoroquinolones in vitro, and levofloxacin, sparfloxacin, and tosufloxacin may be as effective against anthrax as ciprofloxacin by PK-PD analysis. However, additional studies of the in vivo model are necessary to define more clearly efficacy against anthrax and the pharmacodynamic relationship of fluoroquinolones.