Warfarin

What is warfarin?

Warfarin is an anticoagulant medicine. It helps treat and prevent blood clots. Coumadin and Jantoven are brand names for warfarin.

How does it work?

Blood clots may form in people who have artificial valves, irregular heartbeats (atrial fibrillation), or clotting disorders. Blood clots that form when they shouldn't can be dangerous. They can cause problems, including:

stroke when blood flow to the brain is blocked
heart attack when blood flow to the heart is blocked
deep vein thrombosis (DVT) when a blood clot forms in a vein in the legs and may travel to the lungs, causing a pulmonary embolism (PE) and blocking blood flow to the lungs.

When is it used?

Warfarin is used to treat and prevent blood clots. People with some kinds of artificial heart valves need to take warfarin. Warfarin is also used to treat heart attacks and certain kinds of stroke caused by atrial fibrillation.

What should I watch out for?

This medicine may cause you to bleed more easily or bleed longer. Because of this risk, there are some precautions that you should take:

Avoid sports and activities that may cause injury. If you fall or are injured, contact your healthcare provider right away. An injury could cause serious internal bleeding without your knowing about it.
If you need emergency care, surgery, lab tests, or dental work, tell the healthcare provider or dentist that you are taking this medicine.
Wear an ID that says that you take this medicine (such as a Medic Alert bracelet).
Call your healthcare provider if you have any serious illness, such as diarrhea, infection, or fever. These problems may change the effect of this medicine.

Warfarin is different from other kinds of medicines because its effect on your body's clotting system can change from week to week even if you keep taking the same amount of medicine. You will need to have blood tests regularly while you take this medicine. The blood test is called the PT/INR. The INR result is used to adjust the dose of warfarin. The INR is normally around 1.0 if you are not taking warfarin. For most people taking warfarin the best INR level is between 2.0 and 3.0, but you may be better off having an INR slightly higher. The desired INR depends on the condition being treated. The medicine should keep the blood just thin enough to prevent clots. If the blood is too thin, you may bleed too easily.

Many medicines interfere with the effect of warfarin, and warfarin may interfere with the effects of many other medicines. While taking warfarin it is very important to:

Tell all healthcare providers, dentists, and pharmacists that you take warfarin.
Carry a note or wear a bracelet that states you are taking warfarin.
Do not take any other medicines, including nonprescription products, vitamins, or natural remedies unless your healthcare provider approves. Warfarin can interact with aspirin, pain relievers, antibiotics, and many other medicines. The interaction may cause bleeding or other serious side effects. However, there may be some conditions for which combining a daily low dose of aspirin with warfarin may be appropriate. Talk with your healthcare provider about this. Also, do not stop taking any medicines or change the amounts you take unless you talk to your provider or pharmacist first.

Vitamin K plays an important role in forming blood clots. Warfarin works by decreasing the action of vitamin K in your body and therefore decreasing blood clots. Therefore, your diet, particularly the amount of vitamin K in your diet, may affect the way warfarin thins your blood. Eat a healthy balanced diet with about the same amount of vitamin K each day. Vitamin K is found in leafy green vegetables, some legumes, green tea, and vegetable oils. Do not make big changes in your diet, such as eating a lot more green leafy vegetables than you usually eat. Foods that have moderate to high amounts of vitamin K include Brussels sprouts, kale, green tea, asparagus, avocado, broccoli, cabbage, cauliflower, collard greens, liver, soybeans and soybean products such as soybean oil, certain other beans, mustard greens, peas (black-eyed peas, split peas, chick peas), turnip greens, parsley, green onions, spinach, and lettuce.

If you miss a dose of your medicine, take it as soon as you remember on the same day. Do not take a double dose of this medicine. Keep a record of the missed dose and report it to your healthcare provider or pharmacist at the next visit. Call your healthcare provider if you miss more than 1 dose.

Drinking too much alcohol may interfere with this medicine. Talk with your provider about this.

Keep warfarin out of the reach of children and pets.

Do not take warfarin if you are pregnant or plan to become pregnant because it can cause birth defects.

When should I call my healthcare provider?

If you are taking warfarin and have any of these side effects, contact your healthcare provider right away:

a serious fall or hard bump to the head
any unusual bruising
bleeding that does not stop, such as from a cut, from your nose, or from the vagina
dark brown or reddish-colored urine
bloody, black, or tarry stools
vomiting
coughing up of blood
fever, diarrhea, or infection
pain or swelling in your feet or legs
dizziness
trouble breathing
chest pain
unusual weakness or tiredness.