Drugs that prevent the coagulation, or clotting, of blood. Although they’re often called “blood thinners,” anticoagulants don’t dilute the blood—they increase the amount of time it takes for blood to form a clot by interfering with the cascade of reactions that causes clotting. They are used to prevent and/or treat a number of conditions, including deep vein thrombosis (clotting in the deep veins of the legs, pelvis, or arms), pulmonary embolism (when a traveling clot cuts off the blood supply to part of the lungs), heart attacks, strokes, and clotting in people using dialysis machines or those with a replacement heart valve.
Clotting is an essential part of the healing process, closing up wounds so that you don’t bleed to death. However, clots can be dangerous if they form in areas where the inner linings of blood vessels have been damaged (which can be caused by stresses such as smoking, high blood pressure, or high blood glucose levels) or in places where blood pools, such as in the atria (the upper chambers of the heart) when the heart’s contractions don’t completely empty them of blood. These clots may narrow blood vessels (restricting blood flow) or a piece of the clot may break off and travel through the circulatory system until it blocks off a blood vessel, leading to problems like stroke and heart attack. People with diabetes are at increased risk for atrial fibrillation, an irregular heartbeat that can allow blood to pool and clot in the atria. Anticoagulant therapy may be recommended to reduce the risk of stroke for people with atrial fibrillation.
Anticoagulants inhibit the production of thrombin (an enzyme, or catalytic molecule, that helps in the formation of fibrin) and the formation of fibrin (the material that makes up the matrix of clots). The main varieties of anticoagulants include heparin, low-molecular-weight heparins such as dalteparin (brand name Fragmin) and enoxaparin (Lovenox), and coumarins (vitamin K antagonists) such as warfarin (Coumadin) and dicumarol. Heparin and low-molecular-weight heparins are given by injection and are usually used as short-term therapy. Coumarins, which are mostly pills (warfarin is also available as an injection), are used for longer-term therapy.
A person’s dose of an anticoagulant must be carefully adjusted to a level that’s just high enough to be effective without unduly increasing the risk of bleeding problems. Because of this, if you are prescribed an anticoagulant, you will need to have your prothrombin time (the time it takes for a sample of your blood to clot) tested frequently in your doctor’s office or at a laboratory when you start taking it. After a suitable dose has been determined, these tests will be scheduled about once a month.
Anticoagulants can increase the risk of bleeding. You may require medical attention if you notice unexpected bruising, dizziness, tiredness, chills, severe or long-lasting skin rash, stomach pain, unusually heavy menstrual periods, black stools, or any unusual bleeding.
Changes in your diet (especially your intake of foods rich in vitamin K such as vegetable oils, legumes, and leafy green vegetables), drinking alcohol, or coming down with a cold or diarrhea can all affect the activity of an anticoagulant.
A number of drugs can also affect the action of anticoagulants. Acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen (Advil, Motrin, and others), and naproxen (Aleve, Naprosyn) can increase the risk of bleeding problems when taken with an anticoagulant. Supplements containing herbs such as feverfew, garlic, ginger, ginkgo, and ginseng have also been shown to augment the effects of some anticoagulants. Vitamin supplements containing vitamin K or vitamin E should also be used with caution.
Tell your physician of all prescription medicines, over-the-counter drugs, and herbal products you are taking before starting anticoagulant therapy. If you start taking an anticoagulant, you will also need to keep the physician monitoring your anticoagulant therapy apprised of any changes in the doses of drugs you already take or of any new medicines you are prescribed by other physicians.