The Stroke-Venom Connection

Dateline: 02/11/99

A substance called ANCROD, derived from snake venom, allows stroke victims to recover their mental and physical abilities. Researchers found that more than 40% of patients who received ANCROD recovered all of their mental faculties versus more than 30% for placebo patients. The researchers hope that snake venom may provide an alternative to Tissue Plasminogen Activator (TPA) which currently is the only FDA-approved treatment for acute stokes.

ANCROD is a substance formulated from the venom of the Malayan pit viper. In previous observations, scientists had noted that the blood of people bitten by the snake failed to clot. Since stokes are caused by blood clots, researchers were hopeful that this anticoagulant might have applications in stoke victims.

The most striking difference between ANCROD and TPA is the method of administration. TPA is normally injected in a single dose, preferably in the first three hours after the onset of a stroke. ANCROD, on the other hand, is administered by IV over a 3 to 5 day period.

While TPA dissolves clots that cause strokes, ANCROD works by reducing the level of fibrinogen in the blood. Since fibrinogen is the clotting factor in the body, lower levels allow the blood to flow more freely through the blood vessels, thereby reducing the chances for clotting.

Scientists found that those patients whose fibrinogen was reduced and maintained at a target level had the most successful treatment after a stroke. The amount necessary to produce this result was determined by both the body weight of the patient and the relative amount of fibrinogen in the patient's blood. During the treatment period, the additional amount of ANCROD needed was based on the relative level of fibrinogen present in the blood at that time.

The target level was 40-70 milligrams of fibrinogen per deciliter of blood. Doctors found that if this level was maintained in the body, the patients regained their mental faculties after the stroke, had less chance of bleeding, and had less chance of another stroke during the therapy period.

Researchers hope to provide an alternative to the use of TPA. They speculate that having a wider range of treatments will benefit patients. Depending on the kind of stoke and the particular patient, one of the two could be more effective than the other.

Patients participated in a follow-up three months after the stroke. Various mental and physical tests were performed to gauge whether these patients had returned to normal and regained their mental faculties.

Researchers noted that patients who received ANCROD were more likely to have a higher risk of bleeding in the brain compared to TPA patients.

What do you think? Given the differences in treatment, do you think ANCROD has a higher risk than TPA? Do you think that other venom sources may prove useful to stroke victims? Come over to the Biology Forum and share your thoughts, opinions, and feelings.

For related information, see:

Experimental Drug Derived From Snake Venom Shows Promise In Reversing Effects Of Stroke
News release about the study.