UPDATE 1-Drug helps monkeys, rabbits survive anthrax -study

* Human Genome Sciences says drug safe in humans

* May add new defense against key biological weapon

* Studies to be used for FDA marketing approval

By Julie Steenhuysen

CHICAGO, July 8 (Reuters) - An experimental antibody treatment helped rabbits and monkeys survive a deadly dose of anthrax bacteria and proved safe in humans, too, researchers at Human Genome Sciences (HGSI.O) said on Wednesday.

The treatment, ABthrax or raxibacumab, works by preventing toxins produced by anthrax bacteria from causing cell damage and death.

It is designed to work with antibiotics to improve the chances of survival in people infected with anthrax, a deadly bacteria that is a top choice as a biological weapon because it can be made into a fine, airborne powder.

"This adds an important new treatment to the arsenal of things we can use in treating anthrax," Sally Bolmer, a company researcher whose study appears in the New England Journal of Medicine, said in a telephone interview.

Anthrax is a common disease of animals and people can catch it by inhaling the spores, getting them on the skin or ingesting them.

Quick treatment with antibiotics easily cures the infection but, by the time people develop symptoms, it is usually too late as the bacteria has pumped toxins into the body. ABthrax is designed to latch onto the toxins and disable them.

"This is a different mechanism of action than antibiotics, which have been the mainstay of treatment," Bolmer said.

'VERY SIGNIFICANT'

Bolmer said 44 percent of rabbits and 64 percent of monkeys that got a single shot of raxibacumab survived anthrax exposure that was 200 times the average lethal dose.

"That's a very significant survival benefit. In other areas of medicine like cardiovascular disease, an improvement in mortality of 1 or 2 percent is considered medically important," she said.

The company also tested the treatment in 300 healthy people who got single or double doses or raxibacumab and found it caused no serious side effects.

Bolmer said rare side effects such as headache, pain at the injection site and mild itching were about the same in people who got raxibacumab and in those who got a placebo treatment.