On April 27, the U.S. Food and Drug Administration approved Levaquin (levofloxacin) to treat patients with plague. The drug was approved under the agency’s Animal Efficacy Rule, which allows efficacy findings from adequate and well-controlled animal studies to be used in cases where it is not feasible or ethical to conduct trials in humans. There are only 1,000 to 2,000 cases of plague worldwide, making it not possible to conduct adequate efficacy trials in humans. Read more.