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Report Cites Poor Adherence to Anthrax Prophylaxis

Kate Traynor

A study reported in this month's issue of Emerging Infectious Diseases found that 56 percent of the people who began antimicrobial prophylaxis after suspected exposure to Bacillus anthracis spores last year did not complete the recommended 60-day course of therapy, often because of an adverse drug reaction.

Also according to the report, four in seven people who took at least one dose of the recommended medication—usually ciprofloxacin or doxycycline—reported having at least one adverse event within 60 days of starting treatment.

The report's authors, from the Centers for Disease Control and Prevention, noted that the frequency of adverse events during the prophylaxis campaign was greater than the 16.5-percent overall rate cited in the product labeling for ciprofloxacin. The labeling for doxycycline does not specify adverse-event rates.

Thirty-two percent of the 3,032 people who had an adverse event during the prophylaxis campaign reported diarrhea or stomach pain. The next most common adverse event was nausea or vomiting, reported by 27 percent of the 3,032; followed by headache, 25 percent, and dizziness, 22 percent.

In addition to adverse events, the other self-reported reasons for stopping prophylaxis were a perceived low risk for anthrax infection and a fear of long-term adverse effects from extended antimicrobial use.

The research team sought adherence and adverse-event data from the roughly 10,000 people for whom prophylaxis was recommended after suspected exposure to B. anthracis spores during last year's bioterrorist attacks in Florida, New York, New Jersey, Connecticut, and Washington, D.C. Data on 10, 30, and 60 days of prophylaxis were collected by interview for 6,178 people.

A total of 787 people were prescribed antimicrobial prophylaxis but did not start therapy. Ten percent of these persons picked up the initial supply of medication but did not use any of it.

Initially after each anthrax-related attack, ciprofloxacin was offered to all victims except those with a contraindication to use of the drug. When test results confirmed the susceptibility of each batch of anthrax spores to doxycycline, officials or clinicians urged most victims to take that drug instead of ciprofloxacin, and many did.

The transition to doxycycline was highest—82 percent—at the Hart Senate Office Building in Washington, even though the 600 people who were exposed there were initially given a 60-day supply of ciprofloxacin.

After 30 days of prophylaxis, people whose most recent therapy was doxycycline were more likely than ciprofloxacin users to suffer from a drug-related gastrointestinal problem. People whose most recent prophylactic medication was ciprofloxacin were more likely than doxycycline users to report fainting, dizziness, light-headedness, seizures, or joint problems.

Four people had a serious adverse event related to antimicrobial prophylaxis, and all recovered fully from the incident.

The researchers speculated that "some portion of the adverse events may also be ascribed to above-average symptom awareness related to fear of contracting anthrax." Because the adverse-event rates were high in this population, the researchers suggested that future efforts at monitoring the effects of antimicrobial prophylaxis campaigns be supplemented with a "management strategy."