Aspirin and Antiplatelet Medications

Aspirin for the Prevention and Treatment of Heart Attacks and Strokes (Coronary and Cerebral Vascular Disease)

Medical Author: Dennis Lee, MD
Medical Editor: Jay Marks, MD

• What is aspirin?
• What are platelets and antiplatelet medications, and how do they work?
• What is atherosclerosis?
• What is coronary heart disease?
• What is cerebral vascular disease?
• When is aspirin used for preventing and treating blood clots?
• How effective is aspirin for preventing heart attacks among healthy people?
• What are the side effects of aspirin?
• What is aspirin allergy?
• What is the optimal dose of aspirin for treating and preventing heart attacks and strokes?
• Who should be taking aspirin to prevent heart attacks and strokes?
• Who should not be taking aspirin?
• What interactions might aspirin have with other medications?
• What can be done to reduce the risk of ulcers from long-term aspirin therapy?
• What are the limitations of aspirin treatment?
• What is aspirin resistance?

What is aspirin?

Aspirin (known chemically as acetyl salicylic acid and often abbreviated as ASA) belongs to a class of medications called nonsteroidal anti-inflammatory drugs or NSAIDs. Aspirin and other NSAIDs, for example, ibuprofen (Motrin, Advil) and naproxen (Aleve), are widely used to treat fever, pain, and inflammatory conditions such as arthritis, tendonitis, and bursitis. In addition to its effects on fever, pain, and inflammation, aspirin also has an important inhibitory effect on platelets in the blood. This antiplatelet effect is used to prevent the platelets from initiating the formation of blood clots inside arteries, particularly in individuals who have atherosclerosis or are otherwise prone to develop blood clots in their arteries.

What are platelets and antiplatelet medications, and how do they work?

What are platelets?

Platelets are particles (actually remnants of cells) circulating in the blood that are necessary in order for blood clots to form. Platelets initiate the formation of blood clots by clumping together, a process called platelet aggregation. Clumps of platelets then are further bound together by a protein (fibrin) formed from clotting factors present in the blood. The clumps of platelets and fibrin make up the blood clot.

Blood clots are important because they stop us from bleeding when we get cut. However, if a blood clot forms inside an artery , it blocks the flow of blood to the tissue that the artery supplies, and that can damage the tissue. For example, a blood clot that forms in a coronary artery supplying blood to heart muscle causes a heart attack, and a blood clot that forms in an artery supplying blood to the brain causes a stroke.

What are antiplatelet agents?

Antiplatelet agents are medications that block the formation of blood clots by preventing the clumping of platelets. There are three types of antiplatelet agents: aspirin, the thienopyridines, and the glycoprotein IIb/IIIa inhibitors. These agents differ in four ways: the way in which they prevent platelets from clumping, their potency (how strongly they prevent clumping), how rapidly they work, and their cost.

How do antiplatelet agents work?

Aspirin

Aspirin prevents blood from clotting by blocking the production of thromboxane A-2, a chemical that platelets produce that causes them to clump. Aspirin accomplishes this by inhibiting the enzyme cyclo-oxygenase-1 (COX-1) that produces thromboxane A-2. While other NSAIDs also inhibit the COX-1 enzyme, aspirin is the preferred NSAID for use as an antiplatelet agent because its inhibition of the COX-1 enzyme lasts much longer than the other NSAIDs. Thus, aspirin's antiplatelet effect lasts for days while the other NSAIDs' antiplatelet effects last for only hours.

Thienopyridines

In addition to thromboxane A-2, platelets also produce adenosine diphosphate (ADP). When ADP attaches to receptors on the surface of platelets, the platelets clump. The thienopyridines, for example, ticlopidine (Ticlid) and clopidogrel (Plavix), block the ADP receptor. Blocking the ADP receptor prevents ADP from attaching to the receptor and the platelets from clumping.

Glycoprotein IIB/IIa Inhibitors

The glycoprotein IIb/IIIa inhibitors such as abciximab (Reopro) and eptifibatide (Integrilin) prevent clumping of platelets by inhibiting a different receptor on the surface of platelets, the receptor for glycoprotein IIb/IIIa. The glycoprotein IIb/IIIa inhibitors that are approved by the FDA must be given intravenously.

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