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About warfarin (coumadin)

Warfarin is a blood thinner.  It works by interfering with the function of Vitamin K.  Vitamin K is made by the liver and is a essential component of the normal clotting factors needed to clot your blood. Warfarin may be prescribed if you have a blood clot or if you have a clotting disorder, or sometimes if you have an abnormal heart rhythm (atrial fibrillation) or an implanted mechanical heart valve.

The length of time you are on warfarin varies patient to patient. Some people require warfarin for only a few months; others need lifelong treatment. This decision may be made in concert with your vascular surgeon, primary care physician, hematologist and cardiologist.

When you first start warfarin, it typically takes several days for the medication to take effect. The level in your blood stream is monitored with a blood test called protime (PT) or international ratio (INR). The goal INR is typically 2-3. During the initial start-up time, you are also started on or "bridged" with an injectable medication called Lovenox (Enoxaparin). This medication is administered by you or your family twice a day and is continued until the warfarin level is theraputic. It may also be used at times when your INR drifts too low.

When you first start warfarin, the INR may need to be checked every day or every other day. Once you reach a stable level of warfarin, it is checked less frequently (once or twice a month). Typically, you identify a lab near you where your "standing order" for the INR is kept. If you are going to be on warfarin for a while, sometimes purchasing a home monitor and doing the blood test yourself at home is a good option. Always take your warfarin at night and always have the INR drawn in the morning. That way, your lab results are available by the afternoon, so that we can adjust your level if we need to. If you are working with our office to monitor your warfarin, please make sure we have a reliable way to reach you on the days you have your INR drawn.

Side effects of warfarin include bleeding problems, rash or hives, easy bruising, nausea, flu like symptoms/fatigue, joint or muscle aches, diarrhea, gas, hair loss, and change in the sensation of taste.  Rarely, starting warfarin is associated with painful red or black sores in the skin of the legs, buttock or breasts which can lead to large open wounds (warfarin necrosis). The chances of developing this complication is mitigated by use of Lovenox to bridge the coumadin.

If you develop uncontrolled bleeding on warfarin, or if you are involved in a major trauma or suffer a head injury while taking this medication, you should seek immediate medical attention.

There are other newer oral anticoagulants which are currently being studied as alternatives to warfarin (Arixtra, Xarelto, Pradaxa). They are not yet FDA approved for all applications, but are used in some patients who cannot take warfarin.

Tips while on warfarin:

1. Talk with your doctor if you are planning to radically change your diet or if your weight has changed significantly.

2. Carry a card in your wallet or a bracelet on your wrist stating that you are on warfarin. This may be important if you are in an accident.

3. Any time a new medication is added to your regimin, ask your pharmacist or physician about potential interactions with warfarin. For example, many antibiotics interact with warfarin, and your protime may need to be checked more closely while you are on these medications.

4. If you develop spontaneous bleeding (prolonged nosebleed or bleeding from the rectum), or if you are in a major accident or suffer head injury while on warfarin, seek medical attention.

5. Take acetaminophen rather than ibuprofen, if you can. Limit the use of other medications that thin your blood while you are on warfarin. See the list to the right. 

6. Avoid high-risk activities, such as high contact sports, boxing, sky diving.

7. Get your protime checked in the morning, so that results from the blood test are available before the close of the day. 

8. Take your warfarin at the same time every day.

9. If you are anticipating any type of procedure, even dental work or an epidural, be sure to alert your treating physician and the person monitoring your coumadin. 

Some foods contain a lot of Vitamin K and will alter your coumadin levels. Our general philosophy is not to eliminate these foods entirely from your diet, but to be aware of them and to eat a consistent amount of them every day. In other words, do not binge on a salad-only diet for 2 weeks, then not eat green leafy vegetables at all for a month. Dietary concerns are especially important at times like travel, when you may be eating differently than you normally do at home. Staying in range on warfarin is vital in ensuring that the medication is working for you and also in avoiding serious bleeding complications.

 Some foods that interact with warfarin:

Apple (green)




Brussel sprouts



Collard greens, turnip greens

Garbanzo beans

Green pepper













Swiss chard


Some foods, medications, and supplements also potentiate the effects of warfarin, increasing the risk for bleeding problems:






Coenzyme Q10


Evening primrose oil



Green tea


Horse chestnut



Omega 3

Non-steroidal medications (aspirin, ibuprofen, naproxen, celebrex)


Ginkgo biloba



St John's wort


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