US FDA approves raxibacumab for treating inhalational anthrax

By Helen Albert, Senior medwireNews Reporter

The US Food and Drug Administration (FDA) have approved the monoclonal antibody raxibacumab for treatment of inhalational anthrax, caused by breathing in spores of Bacillus anthracis.

The new drug is similar to a human antibody that identifies and neutralizes foreign material, such as bacteria and viruses, and is designed to target the protective antigen component of the lethal toxin of B. anthracis.

Raxibacumab is the first monoclonal antibody to be approved through the FDA's Animal Efficacy Rule, which allows drugs to be approved on the basis of good quality animal studies that have been conducted when testing in humans with the disease is not possible or ethical.

The FDA granted fast track and orphan product designation and priority review to raxibacumab, which they said has shown the potential to fill an unmet medical need and provide effective treatment when no other therapies are available.

In two studies in monkeys and rabbits, 64% and 44% of animals given raxibacumab survived, respectively, compared with no animals in either placebo group.

When rabbits were given a combination of antibiotics and raxibacumab, 82% survived compared with 65% of those that received antibiotic treatment alone.

Although raxibacumab could not be tested in humans with anthrax, it was tested for possible side effects in 326 healthy volunteers. Adverse effects were not severe and included rash, pain in the extremities, itching, and drowsiness.

Anthrax is a known bioterrorism threat due to the spores being resistant to destruction by simple methods and being easily spread through the air.

"In addition to antibiotics, raxibacumab will be a useful treatment to have available should an anthrax bioterrorism event occur," said Edward Cox from the FDA's Center for Drug Evaluation and Research.

"Although antibiotics are approved to prevent and treat anthrax infection, raxibacumab is the first approved agent that acts by neutralizing the toxins produced by B. anthracis."

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