Human Genome Sciences has announced the results of two pivotal animal efficacy studies, which showed the life-saving potential of the human monoclonal antibody drug Raxibacumab ( ABthrax ), as well as the results of human safety studies, which supported the use of Raxibacumab in the event of life-threatening inhalation anthrax disease.

The results have showed that a single dose of Raxibacumab was highly effective as a treatment for inhalation anthrax in both rabbits and monkeys. Raxibacumab acts quickly to provide a significant survival benefit to animals showing clinical signs of disease caused by exposure to a dose of aerosolized anthrax spores that was approximately 200 times the median lethal dose.
The safety profile shown in healthy human volunteers provides support for use of Raxibacumab in the clinical setting of immediately life-threatening inhalation anthrax disease.

Raxibacumab represents a new way to address the anthrax threat. While antibiotics can kill the anthrax bacteria, they are not effective against the deadly toxins that the bacteria produce. Raxibacumab targets anthrax toxins after they are released by the bacteria into the blood and tissues. In an inhalation anthrax attack, people may not know they are infected with anthrax until the toxins already are circulating in their blood, and it may be too late for antibiotics alone to be effective.

Anthrax infection is caused by a spore-forming bacterium, Bacillus anthracis, which multiplies in the body and produces lethal toxins. Most anthrax fatalities are caused by the irreversible effects of the anthrax toxins. Research has shown that the bacteria produce protective antigen, the key facilitator in the progression of anthrax infection at the cellular level. After protective antigen and the anthrax toxins are produced by the bacteria, protective antigen binds to the anthrax toxin receptor on cell surfaces and forms a protein-receptor complex that makes it possible for the anthrax toxins to enter the cells. Raxibacumab blocks the binding of protective antigen to cell surfaces and prevents the anthrax toxins from entering and killing the cells.

Source: Human Genome Sciences, 2009

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