The FDA has approved Anthrasil, Anthrax Immune Globulin Intravenous (Human), to treat patients with inhalational anthrax in combination with appropriate antibacterial drugs.

Inhalational anthrax is a rare disease that can occur after exposure to infected animals or contaminated animal products, or as a result of an intentional release of anthrax spores. It is caused by breathing in the spores of the bacterium Bacillus anthracis. When inhaled, the anthrax bacteria replicate in the body and produce toxins that can cause massive and irreversible tissue injury and death.

To support the nation’s preparedness against a possible anthrax attack, the U.S. Department of Health and Human Services’ Biomedical Advanced Research and Development Authority (BARDA) purchased Anthrasil under Project BioShield in 2011 as an experimental drug for the U.S. Strategic National Stockpile. Because Anthrasil was not approved, its use prior to today’s approval would have required an emergency use authorization from the FDA.

Anthrasil is manufactured from the plasma of individuals vaccinated against anthrax. The plasma contains antibodies that neutralize toxins produced by the anthrax bacteria.

“Today’s approval provides an important additional treatment to other FDA-approved therapies for inhalational anthrax, a life-threatening disease,” said Karen Midthun, M.D., director of the FDA’s Center for Biologics Evaluation and Research. “This product will be stored in U.S. Strategic National Stockpile to facilitate its availability in response to an anthrax emergency.”

The efficacy of Anthrasil was studied in animals because it was not feasible or ethical to conduct adequately controlled efficacy studies in humans. Rabbits and monkeys were exposed to a lethal aerosolized dose of B. anthracis spores, then treated with Anthrasil or a placebo, and evaluated for survival. Survival in anthrax-infected monkeys treated with Anthrasil ranged from 36% to 70% compared to 0% survival in the placebo group with a trend toward increased survival at higher doses of Anthrasil. Rabbits treated with a moderate dose of Anthrasil after infection exhibited 26% survival compared to 2% survival in the placebo group. Another study in rabbits showed that a combination of Anthrasil and antibiotics resulted in 71% survival compared to 25% survival in animals treated with antibiotics alone.

The results of studies in research animals provided sufficient evidence that Anthrasil is reasonably likely to benefit humans with inhalational anthrax. The FDA’s Animal Rule allows efficacy findings from adequate and well-controlled animal studies to support FDA approval when it is not feasible or ethical to conduct trials in humans.

The safety of the product was tested in 74 healthy human volunteers. The most commonly observed side effects were headache, back pain, nausea and infusion site pain and swelling.

The product is manufactured by Cangene, based in Winnipeg, Canada. It was developed with support from BARDA within HHS’ Office of the Assistant Secretary for Preparedness and Response.