Using Drugs to Control Clotting

Sometimes drugs are needed to keep blood from clotting too readily. If blood clots too readily, life-threatening clots may form in arteries of the heart, brain, or lungs. As a result, the risk of a heart attack, a stroke, or pulmonary embolism is increased. Several different types of drugs can help control clotting.

Antiplatelet drugs make platelets less sticky and thus less likely to clump together and block a blood vessel. The most commonly used antiplatelet drug is aspirin. Other antiplatelet drugs include clopidogrel, dipyridamole, abciximab, and tirofiban.

Anticoagulants make blood less likely to clot. Although sometimes called "blood thinners," anticoagulants do not really thin the blood. Instead, they inhibit the activity of proteins in the blood that help blood clot (clotting factors). Commonly used anticoagulants are heparin and warfarin. Heparin is injected under the skin or given intravenously for a short time, usually in a hospital. Warfarin is given by mouth, usually for a longer time after discharge from the hospital. The effects of these drugs must be closely monitored. If the dose is too high, excessive bleeding can occur. If the dose is too low, it may not prevent clots. So people who take them must have blood tests periodically. These tests measure how long blood takes to clot. The dose of the drug is adjusted on the basis of test results. A new type of anticoagulant, low-molecular-weight heparin, does not have to be monitored as much. It is injected under the skin. Lepirudin and argatroban are a new type of anticoagulant that specifically inhibits the activity of one activated clotting factor called thrombin. Thrombin helps in the formation of fibrin, an integral part of a clot. These drugs are used instead of heparin if heparin causes the platelet count to become low.

Thrombolytic (fibrinolytic) drugs can help dissolve a blood clot. Thrombolytic drugs, such as streptokinase and tissue plasminogen activator, are sometimes used when blood clots cause a heart attack or stroke. These drugs may save lives, but they also increase the risk of severe bleeding.