12/17/2012 -

A first-of-its-kind countermeasure has been approved by the U.S. Food and Drug Administration (FDA) to treat the most lethal form of anthrax.

Raxibacumab, created by Rockville, Md.-based Human Genome Sciences, was approved for use after laboratory tests showed that animals treated with the antibodies were more likely to survive anthrax exposure, the FDA announced on Friday.

Untreated inhalational anthrax has a 90 percent mortality rate, but deaths from anthrax can be reduced to around 75 percent if antibiotics like doxycycline and ciprofloxacin are startedwithin 48 hours of exposure.

Antibiotics kill the anthrax bacteria in the body but raxibacumab works by neutralizing the toxins created by the bacteria. The FDA thinks it could reduce the mortality rate even further.

Raxibacumab is a monoclonal antibody, a protein that “closely resembles a human antibody that identifies and neutralizes foreign material,”according to the FDA.

In studies using rabbits, 82 percent survived exposure to inhalational anthrax after being treated with raxibacumab. Only 65 percent survived using antibiotics alone. In another study, 64 percent of monkeys treated with raxibacumab survived.

All of the surviving animals developed their own toxin-neutralizing antibodies.

Raxibacumab is the first anthrax anti-toxin developed underProject Bioshield, an initiative authorized by President George W. Bush to develop and stockpile countermeasures for a nuclear, biological, or chemical attack.

It’s also the first monoclonal antibody approved under the FDA’s Animal Efficacy Rule, which allows animal studies when it’s not feasible or ethical test on people. Adequate efficacy trials for raxibacumab wouldn’t be possible in humans because of its rarity and lethality, the FDA says.

“Our nation took a monumental step forward today in preparing for the health impacts of bioterrorism,” said Department of Health and Human Services Assistant Secretary Nicole Luriein a statement. “This newly approved drug prevents the harmful effects of anthrax toxins and thus raises the likelihood that people who become infected with anthrax will recover.”

Earlier this year, GlaxoSmithKline acquired Human Genome Sciences and in October the company told government officials that it would becutting more than 100 employees.

The approval of raxibacumab will have no impact on those plans, a spokesman said by e-mail.

image:CDC Public Health Image Library - Under a very high magnification of 31,207X, this scanning electron micrograph depicted spores from the Sterne strain of Bacillus anthracis bacteria.