Coumadin is a brand name for warfarin, an anticoagulant drug that thins the blood and helps prevent blood clots from forming. It blocks the ability of vitamin K to activate several clotting factors, which are the proteins in blood that cause it to clot. This reduces the risk of strokes, heart attacks and blood clots in the legs and lungs. The dose of warfarin is determined by a blood test called the International Normalized Ratio, or INR, which measures how fast the blood clots.
The most common complication of warfarin use is bleeding, which may be life-threatening. The risk of bleeding is highest during the first few months after starting the drug, but bleeding can occur at any time. Each year, about one to three out of every 100 individuals taking warfarin develop major bleeding requiring a blood transfusion or hospitalization. Bleeding in the brain, the most serious complication, occurs in one to five per 1,000 people per year. At least half of brain hemorrhages due to warfarin are fatal, and people who survive them often have long-term disabilities.
An excessive dose of warfarin, reflected by an INR value above the target range, is the most important predictor of bleeding. Certain health problems increase the INR and the anticoagulant effect of warfarin and may cause bleeding. For example, sick patients with poor nutrition often become vitamin K deficient, which increases the anticoagulant effect of warfarin and the risk of bleeding. A prior history of bleeding, especially from the stomach or intestines, is also a risk factor for bleeding.
People with high blood pressure, stroke, cancer, kidney or liver problems, those who experience frequent falls and those who abuse alcohol are more likely to develop bleeding problems on warfarin. People older than 65 are more sensitive to the effects of warfarin and have a higher risk of bleeding, especially in the brain.
The use of aspirin or anti-inflammatory medications such as ibuprofen increases the risk of major bleeding, particularly from the stomach and upper digestive tract. Other medications and herbal supplements, including many antibiotics as well as fish oil and ginko biloba, interact with warfarin to increase its anticoagulant effect. Genetic factors also can increase sensitivity to warfarin. People with these genetic differences usually require lower doses and have a higher risk of bleeding, especially during the first several weeks of treatment.
Easy bruising and prolonged bleeding from minor cuts and injuries are common side effects of warfarin. Extensive large bruises, especially without a known cause, or bleeding that takes an unusually long time to stop indicate an excessive warfarin effect. Nosebleeds, bleeding gums, and heavy menstrual periods are other common types of bleeding.
Experiencing red or black tarry stool, or red or dark brown urine, vomiting blood or coffee ground-like material, and coughing up blood are signs of major bleeding that require immediate medical attention. Pain and swelling in any area of the body, weakness, dizziness, difficulty breathing and severe headache may be signs of serious bleeding that are not immediately obvious. Bleeding is most common after trauma but may occur without an obvious cause at any site in the body.
Bleeding on warfarin occasionally reveals a previously unrecognized problem. For example, blood in the stool may be due to a previously unsuspected colon cancer.
The treatment of bleeding depends on the site, severity and INR value. Minor bleeding is usually controlled by temporarily stopping warfarin and counteracting its effect with small doses of vitamin K. Patients with major bleeding require urgent treatment with vitamin K, which can be infused through a vein. Transfusing plasma, which is the liquid part of blood, replaces the clotting factors depleted by warfarin. Special products that contain high concentrations of activated clotting factors also can be used to rapidly stop bleeding.
To reduce the risk of bleeding, warfarin should be taken exactly as instructed at the same time each day. The INR test must be performed regularly, especially after a change in warfarin dose. It is important to eat a balanced diet with a consistent daily amount of green vegetables such as broccoli, asparagus, spinach and lettuce, which are rich in vitamin K. Changes in dietary vitamin K will affect the anticoagulant effect of warfarin.
Your health care provider should be informed of any changes in medications or use of herbal products. A short course of antibiotics may dramatically increase the effect of warfarin and require a dose adjustment.
Avoid sports and activities with a high risk of injury while taking warfarin, and wear medic alert identification. It is especially important to take precautions to avoid head trauma. Inform all your health care providers that you are taking warfarin. To prevent excessive bleeding, warfarin is usually stopped before surgery or other invasive medical procedures. Online educational resources provide detailed information about food and medication interactions with warfarin and prevention of bleeding.
- "Thrombosis and Haemostasis"; Bleeding with Anticoagulation Therapy; Gualtiero Palareti & Benilde Cosmi; Volume 102; 2009
- "Journal of Thrombosis and Haemostasis"; Bleeding in Patients Using Vitamin K Antagonists; Marcel Levi; Volume 7 (Suppl. 1); 2009
- "Chest"; Pharmacology and Management of the Vitamin K Antagonists; Jack Ansell, et al.; Volume 133; 2008