A bioterrorist attack involving anthrax spores sent to various targets by mail in October 2001 resulted in 22 cases of confirmed anthrax poisoning, including five fatal infections. The Centers for Disease Control and Prevention (CDC) coordinated the health care response to patients exposed to anthrax. Tierney and colleagues reviewed the adverse events associated with treatment for anthrax exposure.

Specific exposure criteria were defined by the CDC in consultation with other health authorities. Those at risk for significant exposure to inhalational anthrax received a 60-day course of antibiotic therapy. Concern arose that this therapy might not provide sufficient protection when it became apparent that compliance with the antibiotic regimen was suboptimal, and there was evidence that anthrax spores could persist for more than 60 days, then germinate and cause inhalational anthrax poisoning.

The CDC provided two treatment regimens for extended protection against anthrax. The first option involved an additional 40 days of antibiotic therapy (i.e., ciprofloxacin, doxycycline, or amoxicillin), while the second option combined extended antibiotic therapy with three doses of anthrax vaccine, spaced at two-week intervals. An informed consent educational program was provided to 5,420 exposed persons, of whom 1,727 (32 percent) opted to undergo extended treatment. Most of the enrollees chose to receive only extra antibiotics. Anthrax vaccine was given to 199 persons. Surveillance for adverse events was accomplished via a telephone hotline and post-treatment interviews.

During surveillance, 71 potential adverse events were identified. Twelve of these events were classified as serious, but only two were assessed to be treatment-related. One patient on extended treatment with doxycycline developed diarrhea and chest pain. Extended ciprofloxacin therapy led to allergic interstitial nephritis and acute renal failure in another patient. No serious adverse events were associated with use of anthrax vaccine.

The authors conclude that two serious adverse events occurred in 1,727 persons receiving extended antibiotic treatment for anthrax exposure. Surveillance of participants is to be continued over an additional two years to monitor for any delayed adverse events.