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Federal Health Agencies Clarify Doxycycline Regimens for Anthrax Exposure

Cheryl A. Thompson

The Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) yesterday specified dosage regimens for the use of doxycycline in preventing and treating anthrax exposure.

FDA's action came one day after Health and Human Services Secretary Tommy G. Thompson is said to have told a Senate committee that the agency is approving new labeling for the use of several anti-infectives other than ciprofloxacin to treat anthrax.

Today's Morbidity and Mortality Weekly Report (PDF),available online yesterday, offers "interim" recommendations for preventing inhalational anthrax after exposure to aerosolized Bacillus anthracis.

After a suspected or confirmed exposure but before information is available on the susceptibility of the B. anthracis strain to anti-infectives, adults and children should start an oral regimen of ciprofloxacin or doxycycline, according to CDC. Anti-infective therapy should continue for 60 days if the exposure has been confirmed by a laboratory.

CDC recommends that adults receive ciprofloxacin 500 mg or doxycycline 100 mg twice daily. Children should receive ciprofloxacin 10–15 mg/kg every 12 hours or doxycycline. The pediatric regimens for doxycycline are 100 mg twice daily for children older than 8 years and heavier than 45 kg, or 100 pounds; and 2.2 mg/kg twice daily for children older than 8 years but 45 kg or less and those 8 years or younger.

If the B. anthracis strain obtained from a child is found to be susceptible to penicillin, CDC recommends that treatment be changed to amoxicillin 80 mg/kg per day, divided into three doses to be given every eight hours but not to exceed 500 mg per dose.

Cephalosporins and trimethoprim–sulfamethoxazole should not be used to prevent inhalational anthrax because B. anthracis is not susceptible to these anti-infectives, CDC noted.

The FDA advisory discussed doxycycline for the treatment, not prophylaxis, of all types of anthrax exposure—inhalational, cutaneous, gastrointestinal, and oropharyngeal.

FDA's recommended dosage of doxycycline for treating severe cases of anthrax in adults is 100 mg every 12 hours. For children weighing less than 45 kg, the recommended dosage is 2.2 mg/kg every 12 hours. The duration of treatment was not specified and neither was the dosage for children weighing more than 45 kg.

Product labeling for doxycycline and penicillin already state that these antibiotics are indicated for the treatment of anthrax due to susceptible strains of B. anthracis. Specific dosage information for this indication, however, has been lacking from the labeling. Yesterday's announcement by FDA helps to clarify the appropriate use of one of these antibiotics.