Scientists in a U.S.-funded study said an experimental anthrax treatment from Human Genome Sciences Inc. increased survival in animals infected with the deadly disease. This led them to believe that the drug, a human monoclonal antibody called raxibacumab, might safely cure anthrax poisoning in humans.

In an article published today in the New England Journal of Medicine, researchers said although antibiotics can kill the anthrax bacteria, they are not effective in killing the toxins produced by the bacteria and raxibacumab, specifically targets those toxins once they enter the bloodstream.

The researchers explained that often after an anthrax attack people may not know they are infected until the toxins are circulating in their blood, and it may be too late for antibiotics to be effective.

Sally Bolmer, senior vice president of development and regulatory affairs at Human Genome Sciences Inc., and lead researcher said, "This drug strengthens America's arsenal against bioterrorism that would work in the face of antibiotic-resistant anthrax bacterium."

She explained that the drug works differently than antibiotics. "It [also] acts more quickly than vaccines. So, it is complementary to both of those," Bolmer said.

"If we administered it at the time the animals were exposed to anthrax or even waited until their symptoms developed, we could improve survival in rabbits and monkeys," she said.

The government-funded study although intended for humans was conducted on monkeys due to prohibitions on infecting human subjects with anthrax.  According to the U.S. Centers for Disease Control and Prevention, after the 2001 anthrax attacks, when mailed letters containing anthrax spores caused 22 infections and five deaths, U.S. health officials are trying to stockpile treatments. 

James Davis, executive vice president for Human Genome Sciences said, “We believe the government is very interested in continuing to build its supply of this product, and we are optimistic we will get additional orders.”

Human Genome a Rockville, Maryland-based company as part of a $165 million contract with U.S. Biomedical Advanced Research and Development Authority, announced in 2006 recently completed delivery of 20,000 doses of the drug, also known as Abthrax, to the U.S. Strategic National Stockpile for emergency use.

Bolmer said approval of the drug by the U.S. Food and Drug Administration is pending. Human Genome will use the study results to seek U.S. regulatory approval for Abthrax and the company hopes to gain that clearance in late 2009 or early next year Davis said. 

The researchers said raxibacumab improved survival rates for monkeys by 64 % and nine of the 14 monkeys given the drug were still alive 28 days after exposure to inhaled anthrax, while all 12 monkeys who received a placebo died.

The study also reported that Abthrax improved survival in rabbits with inhaled anthrax by 44%. After 14 days, eight of 18 rabbits were still alive, compared with none of the 18 rabbits who received a placebo. The researchers said animals were intentionally exposed to anthrax in doses that were as much as 200 times the amount shown to cause death. 

The researchers said the drug was also tested in 333 healthy humans to determine how they responded to therapeutic doses equivalent to those given to the animals though the humans were not exposed to anthrax in the study. The only one serious adverse event possibly tied to the drug that was reported, was a case of cholecystitis, an inflammation usually associated with gallbladder stones which doctors said was more likely caused by the patient’s underlying medical condition rather than the drug,.

The study found based on animal research that a single dose of Abthrax would provide at least 95 % of human’s sufficient levels of the drug in their blood for 28 days.