May 9, 2000 -- A venomous snake from a humid Southeast Asian nation is the unlikely source of a new drug that appears to be able to protect people from some of the worst ravages of strokes.
Ancrod, made from the venom of the Malaysian pit viper, was discovered when doctors found that the blood of people who had been bitten by this snake did not clot normally for several days afterward.
Researcher David G. Sherman, MD, tells WebMD that patients treated with ancrod are more likely to survive the most common type of stroke with their normal abilities and functions intact. The drug also seems to cause less bleeding in the brain than other drugs used to treat stroke, says Sherman, who is professor and chief of the Division of Neurology at the University of Texas Health Science Center at San Antonio.
In the study, published in TheJournal of the American Medical Association, Sherman and colleagues looked at 500 patients with sudden ischemic stroke, which occurs when part of the brain is denied blood because something has gone wrong with its blood vessels. That something is often a tiny bit of fat or a small blood clot that lodges in one of the vessels -- and becomes the organizing point for a much bigger, more dangerous clot.
The clot-busting drug rtPA (tissue plasminogen activator) can often drill out these clots if given soon after symptoms begin, but it also increases the risk of bleeding into the brain. Sherman tells WebMD that ancrod works earlier by starving the clots of a substance called fibrinogen.
Clots don't amount to much unless they can string themselves up along a scaffolding within the blood vessel and get organized. One part of this scaffolding is made of strands of fibrin, a protein that is important in the clotting of blood. This requires fibrinogen, which becomes fibrin after a chemical reaction.
Sherman says that ancrod chops an end off of the fibrinogen molecule. That means blood levels of usable fibrinogen drop very quickly, depriving the clot of the support it needs to grow.
Patients in the study did much better if they were treated intravenously with ancrod soon after stroke symptoms began than if they were treated with an inactive saltwater solution. About 42% of the ancrod patients survived the stroke without major damage, compared with about 34% of the comparison patients. Only about 12% of the ancrod patients became severely disabled, compared with nearly 20% of the comparison patients.
In an editorial accompanying the study, Marc R. Mayberg, MD, and Anthony Furlan, MD, point out that this study was conducted mostly in community hospitals in North America. This suggests that if ancrod is approved by the FDA, it could be used in routine hospital practice and not just in university hospitals. Mayberg and Furlan are in the department of neurosurgery at the Cleveland Clinic Foundation.
Sherman tells WebMD that even ancrod will not work if it is given more than three hours after a stroke begins. "This will not help someone who had a stroke last week or last year," he says. "As with rtPA, this treatment must be given quickly, before the lasting damage is done."
The research was funded by Knoll Pharmaceutical Co., which supplied the ancrod used in the study.
Vital Information:
- A drug called ancrod, which is derived from snake venom, is an effective treatment for the most common form of stroke and prevents disability better than the current therapy.
- An ischemic stroke occurs when a blood clot in the brain prevents the delivery of oxygen to brain cells. Ancrod works by breaking up the 'scaffolding' in the blood vessels on which the clot forms.
- As with other stroke drugs, ancrod must be given within three hours after a stroke begins in order to be effective.