The April 1 issue of The Medical Letter will include an article on a new drug for prophylaxis and treatment of inhalational anthrax. Raxibacumab is not a new antimicrobial agent. It is a monoclonal antibody that must be given intravenously and is only available from the CDC. Raxibacumab has been around for a few years; what is new is its approval by the FDA, which comes with the slightly mystifying proviso that it should be used for prophylaxis of inhalational anthrax when alternative therapies are not available or are not appropriate. The alternative therapies are antimicrobial agents like ciprofloxacin or doxycycline and an anthrax vaccine. Apparently what the labeling is getting at is that raxibacumab would become the drug of choice if the anthrax bacillus were bioengineered to be resistant to the antimicrobials.

Bioengineered? Yes, sadly. The only meaningful threat anthrax poses in the developed world is from bioterrorism. Inhalational anthrax is highly lethal, but it is rare. The largest outbreak in history, 70 cases, occurred in the Soviet Union in 1991 in the vicinity of a military facility that was manufacturing anthrax powder for possible use in biological warfare. The anthrax bioterrorism scare in the US, which took advantage of the US Postal Service, occurred in 2001. It resulted in 22 documented cases of anthrax, 11 inhalational and 11 cutaneous, but 10,000 people were given anthrax post-exposure prophylaxis (60 days of antimicrobials).

Neither raxibucamab nor anthrax vaccine is available commercially. Both have to be obtained from the CDC. Anthrax vaccine has been used extensively both for pre- and post-exposure prophylaxis, and it is effective. The FDA recently approved a 4-dose primary series of injections, replacing the previous 5-shot series, and it does require annual boosters. It seems to me that if we are really worried about someone cropdusting our cities with anthrax spores, pre-exposure vaccination would make more sense than rushing crates of raxibacumab to the Atlanta airport or emptying out the ciprofloxacin and doxycycline supplies of our pharmacies. While the authorities consider that impractical suggestion, read about raxibacumab in the April 1 issue of The Medical Letter. I hope we never have to use it.

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