Snake Venom Extract Fights Stroke

An experimental drug derived from the venom of the feared Malayan pit viper shows promise for the treatment of stroke, an analysis of six studies involving over 4,000 stroke victims suggests.

The drug, known as Viprinex, may double the time window during which victims can be treated following the onset of symptoms, researchers say.

The drug, also known by the generic name ancrod, is designed to help people who suffer an acute ischemic stroke, the most common type. It occurs when blood flow to an area of the brain is compromised by a blood clot. This leads to the death of brain cells and brain damage.

Currently, the clot-buster t-PA can be used for ischemic stroke, but time is of the essence: It has to be administered in the first three hours after symptoms strike.

Research suggests Viprinex can be given up to six hours out, says study head Bart M. Demaerschalk, MD, an assistant professor of neurology at the Mayo Clinic in Scottsdale, Ariz.

"By expanding the window beyond three hours and up to six hours, Viprinex would hopefully expand the number of people that can be treated for acute ischemic stroke," says American Stroke Association spokesman Ralph Sacco, MD.

Sacco, director of the stroke service at Columbia-Presbyterian Medical Center in New York, was not involved with the research, presented here at the American Stroke Association's International Stroke Conference 2007.

Venom Milked From Vipers on Snake Farm

Viprinex packs a triple punch against stroke, preventing new clots from forming, breaking down existing clots, and thinning out the blood, thereby improving blood flow to the brain.

It was discovered when doctors found that the blood of people who had been bitten by the Malayan pit viper did not clot normally for several days afterward.

Now, biotech researchers milk the venom from vipers raised on a snake farm in Germany, Demaerschalk says.

"Using their hands, they put a little pressure on the jaw and it squirts out," he tells WebMD. "Ancrod is extracted and purified from the venom."

Slight Reduction in Risk of Death, Disability

For the new analysis, Demaerschalk and colleagues combed the medical literature for studies comparing the venom extract to placebo in ischemic stroke victims.

Results showed that 44% of people treated intravenously with Viprinex died or were severely disabled, vs. 47% of those who were injected with an inactive saline solution -- a difference so small it could have been due to chance.

Demaerschalk says the results may have been skewed by inclusion of trials that allowed people to be treated beyond the six-hour window from symptom onset. One study allowed people to be treated up to two days out.

Just 1% of those given placebo suffered brain bleeds, compared with nearly 5% of those on Viprinex.

But Demaerschalk says this "is not necessarily worrisome," as the risk of brain bleeds with tPA "is even larger, about 6%."

The bottom line, he and Sacco agree, is that further study is needed before the drug is ready for prime time.

Two large studies pitting the venom extract against placebo in over 1,000 people within six hours of symptom onset should offer results within a few years, Demaerschalk says.

SOURCES: International Stroke Conference, Feb. 7-9, 2007, San Francisco. Bart M. Demaerschalk, MD, assistant professor of neurology, Mayo Clinic, Scottsdale, Ariz. Ralph Sacco, MD, spokesman, American Stroke Association; director, stroke service, Columbia-Presbyterian Medical Center, New York City