Clopidogrel prevents platelets (substances in the blood) from clustering. This helps to prevent blood from forming blood clots. Clopidogrel is used in the prevention and treatment of heart attack, stroke, blood clots, and acute coronary syndrome. Clopidogrel is used to prevent strokes and heart attacks in persons who are at high risk. In one large study, clopidogrel was more effective than aspirin in reducing heart attacks. The frequency of side effects of clopidogrel was similar to aspirin; however, stomach and intestinal bleeding probably occurs less often with clopidogrel than with aspirin.
Clopidogrel works by preventing a natural substance called ADP from binding to its receptors on platelets. ADP is one of the chemicals in the body that cause platelets to clump together and start the process of blood clotting. As clopidogrel stops ADP from binding to platelets, it reduces the likelihood of clots forming in the blood. A blood clot that forms inside the blood vessels is known as a thrombosis and can be dangerous, as it can cause a blockage that cuts off the blood supply to an organ. A blockage in the arteries supplying blood to the heart or brain can cause a heart attack or stroke. A blockage in the blood vessels in the extremities, eg legs, may result in gangrene. Blood clots and blockages mainly result from a build up of atherosclerosis on the inside of blood vessels. Atherosclerosis is a build up of cholesterol and fat cells that narrows the blood vessels and makes their interiors rough and bumpy. This makes it more difficult for blood to flow through the vessels, and increases the likelihood of clots forming in the vessels.
Clopidogrel inhibits platelet function by selectively blocking ADP-induced platelet aggregation and is metabolized by the liver to an active form. The action of clopidogrel appears to be permanent in that there is still antiplatelet activity for seven to ten days after the medication has been stopped. Clopidogrel is an anti-platelet drug, that is, a drug that inhibits the ability of platelets to clump together as part of a blood clot. It is similar to ticlopidine (Ticlid) in chemical structure and in the way it works. Unlike ticlopidine, clopidogrel does not cause serious reductions of white cells in the blood and, therefore, routine blood testing to determine if the white blood cell count is low is not necessary during treatment. The risk of heart attacks and strokes (which usually are caused by blood clots) is increased in patients with a recent history of stroke or heart attack and patients with peripheral vascular disease. (Peripheral vascular disease is the same as atherosclerotic arterial disease or "hardening" of the arteries in which the arteries become narrowed. It frequently occurs in the legs and often causes claudication or pain in the legs upon walking).