Examples

Warfarin is taken in pill form.

Heparin can be given through a vein (intravenously) or by injection into fatty tissue (subcutaneously).

How It Works

Although anticoagulants are often called blood thinners, they do not really thin blood. Warfarin prevents the production of certain proteins that are necessary for blood to clot. Heparin and newer low-molecular-weight heparins interfere with the complex process of blood clot formation. Heparin and warfarin prevent new clots from forming and may prevent existing clots from getting larger. They do not break up clots.

Why It Is Used

These medicines are given only after it is certain that a person is not having a hemorrhagic stroke, which is caused by bleeding in the brain. Anticoagulants should only be used when a blood clot is suspected of causing the stroke or transient ischemic attack (TIA).

Treatment with heparin followed by warfarin is often recommended for people whose TIA or stroke was likely caused by a clot formed in the heart. Heparin often is used first (up to 2 days after the stroke) because it can be given quickly into a vein (intravenously), and it has an immediate effect on clotting. Warfarin is used long-term after heparin use is ended.

Heparin may be used if a person is having repeated TIAs or when TIA symptoms seem to be getting worse. This indicates that a blood clot may be getting bigger or that a plaque is unstable, and quick-acting anticoagulants are needed.

Most people with atrial fibrillation should take warfarin to lower their risk for stroke. One exception is people younger than 65 who have atrial fibrillation without any other risk factors for stroke.

People with active stomach ulcers, severe liver or kidney disease, or a history of falls probably should not take an anticoagulant.

How Well It Works

Anticoagulants are effective at preventing the formation of clots in people who have specific heart problems—such as atrial fibrillation—that make clot formation more likely. Warfarin has been shown to greatly reduce the risk of TIA and stroke in people who have atrial fibrillation.

Side Effects

Side effects of anticoagulants include:

• Serious bleeding in the brain, which may result in death.
• Bleeding from ulcers or growths in the digestive system.
• Serious bleeding in other areas of the body.
• The toes turning purple or blue. This is rare and may occur in the first few days of treatment with warfarin because circulation is being affected by the drug.

If you are taking an anticoagulant, call your doctor immediately if you have signs of bleeding, including:

• Blood in urine, or burgundy-colored or tarry stools.
• Bleeding from the nose or gums, or spitting up blood.
• New or increased vaginal bleeding.
• Frequent, severe bruising or tiny red or purple spots on the skin.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Anticoagulants are not as effective as carotid endarterectomy surgery in preventing stroke for people who have significant hardening and narrowing of the carotid arteries (more than 70% of the artery is blocked by plaque buildup).¹

Because anticoagulants increase your chance of bleeding, you need to have regular blood tests to monitor blood-clotting time while taking these medicines. Some safety tips when taking anticoagulants may be helpful, such as taking your medicines at the same time each day and watching for signs of bleeding.

It is important that you know what to do if you miss a dose of anticoagulant.

Anticoagulants should not be given within 24 hours of treatment with tissue plasminogen activator (t-PA).

Do not start or stop taking any medicines or supplements unless you have talked with your doctor. Many different medicines and supplements affect how well warfarin works.

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