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Snake Venom May Help Treat Stroke

Updated:
CHICAGO (AP) — A blood-thinning drug derived from the venom of the Malayan pit viper can reverse symptoms in stroke victims, researchers reported today in the Journal of the American Medical Association.

However, other research suggests that if doctors wait too long to administer the drug, it might kill the patient.

The experimental treatment follows the discovery that blood failed to clot in people bitten by the snake. Scientists figured the venom could be used as an anticoagulant to help stroke victims who have a clot that is blocking blood flow to the brain.

In a study of 500 stroke patients, 42 percent who were given the drug ancrod within three hours after the onset of symptoms regained significant functioning vs. 34 percent of those who got a placebo. The two groups had similar death rates three months after treatment.

The study was led by Dr. David Sherman, a neurologist at the University of Texas Health Science Center in San Antonio, and was conducted in the United States and Canada.

The promising results led ancrod's manufacturer, BASF Pharma, to launch a separate European study to see if it would also work within six hours of symptoms. But the three-month death rate in the ancrod patients was higher than in a placebo group and the study was halted in March.

Linda Mayer, spokeswoman for BASF Pharma's U.S. subsidiary, Knoll Pharmaceutical Co., said deaths were ``minimally higher'' in the ancrod patients. The company is analyzing data from both studies and has not yet applied for federal approval of ancrod for stroke treatment, Mayer said.

Sherman said ancrod should still be considered a promising potential treatment, and stroke experts not involved in the study agreed.

Ancrod is similar to the clot-buster TPA, the only federally approved drug for strokes. TPA dissolves clots, while ancrod lowers blood levels of fibrinogen, a substance that can help form clots. That allows blood to flow more freely.

Both drugs are given intravenously. TPA, like ancrod, has a three-hour treatment window.

About 700,000 Americans have strokes each year. Many end up with paralysis, impaired speech and other debilitating effects. Until the recent use of TPA, there was little doctors could do to treat strokes once symptoms such as numbness and difficulty speaking appeared.

TPA, like ancrod, has also been linked with more deaths after the three-hour window, said Dr. John Marler, associate director for clinical trials at the National Institute of Neurological Disorders and Stroke. He said the studies underscore how critical very early treatment is.

Ancrod may be slightly less likely to produce bleeding in the brain, a potentially fatal complication, said Dr. Thomas Brott, a neurologist with the Mayo Medical School in Jacksonville, Fla., and a member of the American Heart Association's stroke council. In Sherman's study, 5 percent of ancrod patients had brain hemorrhaging vs. 2 percent of the placebo group.

``It may be possible to fine-tune ancrod to make it even safer than it was in the study,'' Brott said.

BASF Pharma keeps a colony of snakes in Germany and milks them regularly to extract the venom. Sherman said the company has not succeeded in making a synthetic version so far.

In an editorial in the journal, Drs. Marc R. Mayberg and Anthony Furlan of the Cleveland Clinic Foundation said they are not convinced ancrod has any clear advantage over TPA but could be another drug at doctors' disposal.

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On the Net: http://www.nlm.nih.gov/medlineplus/stroke.html

BASF Pharma: http://www.knoll.de

JAMA: http://jama.ama-assn.org
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