Anticoagulants are medications that prevent the coagulation, or clotting, of blood. Normally, coagulation is a good thing, since it keeps us from bleeding to death when we scrape our knees, but there are times when it is most emphatically a Bad Thing™.

Coagulation is the process of clot, or thrombus, formation. When it occurs in the normal process of hemostasis, stopping the bleeding from a wound, hemostasis is survival positive. Lack of coagulation is what causes hemophiliacs to bleed excessively from minor injuries.

However, thrombi can wreak havoc on the body in certain situations. When there is stasis of the blood, like in prolonged immobility, thrombi can form in the veins without any injury having occurred. These thrombi are attached to the wall of the blood vessel, but they can break loose. If this happens, the veins carry this clot (or cluster of clotlets) back to the heart, along with all the other returning blood. When the clot gets to the heart, it can get lodged in the lungs (pulmonary embolism) or in the coronary arteries (heart attack), although heart attacks usually occur when a clot forms in a narrowed section of a coronary artery (as opposed to a floating clot). In atrial fibrillation, clots may form in the heart, and may travel from the left ventricle to the brain (stroke). This is usually not considered good.

There are conditions that predispose people to thrombus formation, such as atrial fibrillation, and there are situations, such as open heart surgery or dialysis, when clotting would be VERY VERY BAD. Anticoagulants are used to prevent thrombus formation in these situations, and also when the patient has had thrombotic problems in the past.

When anticoagulants are used, the patient's bloodwork must be monitored closely, to ensure that the patient is not in danger of excessive bleeding. Patients must also be warned not to take salicylates or any other medications that have anticoagulant side effects unless prescribed.


Brand/Generic Drug Names

ardeparin, Lovenox/enoxaparin, heparin, lepirudin, Coumadin/warfarin
Common uses
deep vein thrombosis, pulmonary embolism, myocardial infarction, open-heart surgery, disseminated intravascular coagulation, atrial fibrillation with embolization, transfusion, dialysis
interfere with blood clotting by preventing clot formation
Class contraindications
hemophilia, leukemia with bleeding, peptic ulcer disease, thrombocytopenic purpura, blood dyscrasias, acute nephritis, subacute bacterial endocarditis
Class precautions
alcoholism, elderly, pregnancy
increased anticoagulation: salicylates, steroids, NSAIDs
Adverse Reactions
hemorrhage, agranulocytosis, leukopenia, eosinophilia, thrombocytopenia, diarrhea, rash, fever
Additional Information
Assess PT/PTT daily; hematocrit, platelets and occult blood every 3 mos
Assess vitals, watch for bleeding gums, petechiae, ecchymosis, melena, hematuria
Administer at same time each day to maintain blood levels
Do not massage injection site or aspirate
Evaluate therapeutic response: decrease in deep vein thrombosis
Date of most recent Update
August 05, 2002
Further information is available in the writeup for the specific name(s) of this medication class