Consultants for The Medical Letter on Drugs and Therapeutics reviewed data on the anthrax vaccine following the government's decision to vaccinate more than 2 million members of the armed forces.

Anthrax is caused by the gram-positive, spore-forming bacterium Bacillus anthracis. The spores can persist in nature for many years and may infect grazing animals. Although cutaneous anthrax is the most common form of the disease, inhaled anthrax is the most significant concern for U.S. military forces. Inhaled anthrax can cause fever, cough and weakness within one to six days of infection and may progress in two to three days to respiratory failure, septic shock and multiorgan failure. The mortality rate in persons with untreated inhalation anthrax is about 95 percent.

The anthrax vaccine is produced as a sterile filtrate of cultures of an avirulent strain that elaborates protective antigen. Although no results from controlled trials are available, the vaccine has been licensed by the U.S. Food and Drug Administration since 1970. Experience with the current vaccine in high-risk industries with exposure to imported animal products has shown that anthrax infection has not occurred in workers who received two or more doses of vaccine but has occurred in some unvaccinated workers. A protective antibody response does not usually develop until seven days after the second dose of the vaccine. The vaccine is well tolerated, and erythema and tenderness at the injection site are usually mild. Fever and chills are rare.

Anthrax vaccine is given in a volume of 0.5 mL subcutaneously at zero, two and four weeks, and at six, 12 and 18 months. An annual booster shot is recommended. In emergency exposure, the vaccine should be given immediately and repeated two weeks later with appropriate antibiotic coverage.

The anthrax bacillus is highly susceptible in vitro to penicillin, amoxicillin, chloramphenicol, doxycycline, erythromycin, streptomycin and ciprofloxacin. It is resistant to third-generation cephalosporins.

In animal studies, 30 days of treatment with an antibiotic was generally effective, but vaccination alone was not sufficient. The current recommendation for prophylaxis after exposure is vaccination plus oral doxycycline, in a dosage of 100 mg twice daily, or ciprofloxacin, in a dosage of 500 mg twice daily, for at least 30 days. Symptomatic patients with inhalation anthrax should be treated with ciprofloxacin, in a dosage of 400 mg intravenously every eight to 12 hours, until susceptibility tests are available.

Medical Letter consultants conclude that anthrax vaccine is safe and effective for preexposure prevention of anthrax. Following exposure, an unvaccinated person should receive vaccination and a prolonged course of antimicrobial prophylaxis.