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Coumadin is known as a blood thinner or anticoagulant. That means it is prescribed to prevent the formation or recurrence of blood clots. People who experience a pulmonary embolism or thrombophlebitis in their legs often receive warfarin to reduce the risk of more serious complications. When clots are feared, this medicine may lower the likelihood of a heart attack or stroke.

Coumadin works by blocking key factors necessary for normal blood coagulation. Vitamin K plays an important role in this process. Getting the right dose can be a very tricky process. Too little warfarin may not allow for adequate clot protection, but too much could lead to life-threatening hemorrhage. Like Goldilocks and the porridge it may take some experimentation to get things just right. That requires frequent blood tests for prothrombin times, especially in the early phase of treatment.

Side Effects and Interactions:

Side effects of Coumadin therapy are uncommon if the dose is appropriate and blood tests are carefully monitored. Some people have occasionally reported hair loss, skin rash, itching, nausea, fever, digestive upset, diarrhea, hepatitis, purple toes, red-orange urine, prolonged, painful erections, and mouth ulcers. Report any such symptoms to your physician promptly.

A large number of over-the-counter and prescription medications may interact with Coumadin in a dangerous way. Some drugs, including barbiturates and the anticonvulsant Tegretol (carbamazepine), can reduce the effectiveness of Coumadin and increase the risk of blood clots. Others, such as the antibiotics metronidazole (Flagyl) or co-trimoxazole (Bactrim, Septra, etc.), can increase the blood thinning potential of Coumadin and thereby raise the risk of dangerous bleeding. The drugs Nolvadex (tamoxifen) and Danocrine (danazol) can also increase susceptibility to hemorrhage when a woman is taking Coumadin.

Because aspirin also acts as an anticoagulant, though it works differently from Coumadin, it should be avoided unless your doctor specifically prescribes it and monitors bleeding time. The heart drug Cordarone (amiodarone), the ulcer drug Tagamet (cimetidine), anabolic steroids such as Anadrol-50 (oxymetholone) and antibiotics such as Biaxin (clarithromycin), erythromycin or tetracycline can also make hazardous bleeding more likely for people on Coumadin. Some individuals may also be vulnerable to increased bleeding when they take the antidepressants Paxil (paroxetine), Prozac (fluoxetine) or Zoloft (sertraline). Also beware of quinine derivatives prescribed for the heart.

Patients should be wary of taking thyroid drugs, cholesterol medications and tuberculosis medicines in combination with warfarin. Vitamins E and K could also be problematic. Consult with the prescribing physician before making any changes in the regimen. Coenzyme Q10 may counteract the benefits of warfarin. Anticoagulants such as Coumadin may pose a hazard when taken with the herb ginkgo biloba. An elderly woman on Coumadin had a hemorrhagic stroke after two months of ginkgo. If the extract of the herb hawthorn is taken together with Coumadin, careful monitoring of bleeding time (through PT and INR) is essential. The anticlotting action of the herb horse chestnut (aesculin) may interact with Coumadin to increase the risk of bleeding. This combination should be avoided.

It is possible that juniper berries may interact with Coumadin to increase the risk of bleeding. This possibility remains hypothetical. Licorice binds to serum albumin and may interact with Coumadin. The coumarins in licorice may also potentiate the action of Coumadin, possibly leading to unexpected bleeding. Despite research suggesting that ginseng might reduce platelet aggregation, the only reported interaction with Coumadin resulted in a decreased INR (international normalized ratio, a measure of blood clotting propensity). This suggests that ginseng might possibly counteract the benefit of warfarin. A red clover extract containing coumarin derivatives might in theory interact with the anticoagulant Coumadin. Close monitoring of prothrombin time or INR is advisable.

Psyllium can affect the absorption of Coumadin. To avoid this, psyllium should be taken at least an hour after Coumadin. In theory, garlic could increase the risk of bleeding in people taking anticoagulants such as Coumadin. The herb pau d’arco causes vitamin K-reversible bleeding, strongly suggesting that it would interact with Coumadin to increase the danger of hemorrhage. The anticoagulant activity of astragalus may interact with that of warfarin, increasing the risk of bleeding. This herb capsicum (cayenne) may have the potential to prolong clotting time, so people taking Coumadin should exercise caution before eating quantities of chili peppers. Cayenne also inhibits liver enzymes (CYP1A2) and thus could potentially slow the metabolism of warfarin.

In theory the coumarins in the herb chamomile might potentiate Coumadin’s effect. Careful monitoring of bleeding time (through PT and INR) are recommended if chamomile is to be used together with Coumadin. One woman was hospitalized with internal bleeding after consuming chamomile tea regularly while taking Coumadin. (CMAJ, Apr. 25, 2006) Also in theory, the herb feverfew could increase the risk of bleeding in people taking Coumadin. Because ginger inhibits prostaglandin synthesis and reduces platelet aggregation, caution should be exercised in combining it with warfarin. The combination could result in unexpected bleeding. It is not known whether the coumarins in the herb dong quai might interact with Coumadin. To be safe, any woman taking both dong quai and Coumadin should discuss this situation with her doctor and should have bleeding time (PT and INR) checked frequently, especially when starting or stopping the herb. Goldenseal reportedly limits the effectiveness of the Coumadin. As a general rule, do not take any other medication or herbs without first checking with your physician and pharmacist.

Taking the Medicine:

Although the absorption of Coumadin may be slightly slowed by food, the medicine can be taken at meal time, especially if it upsets your stomach. There are, however, certain foods that may reduce the effectiveness of this drug. Because Vitamin K can counteract the action of warfarin, it is important to get approximately the same amount of this vitamin every day. Be careful not to overdo suddenly on foods that are rich in this nutrient. These include broccoli, cabbage, spinach, collard greens, kale, brussels sprouts and lettuce. This doesn’t mean that you must avoid such healthy vegetables, but don’t suddenly increase your intake without careful monitoring of prothrombin time. (For a more complete list, see our Guide to Coumadin Interactions.) The same warning would hold if you suddenly dropped one of these from your diet completely.

Special Precautions:

Anyone taking Coumadin must monitor his body carefully. Be alert for any early warning signs of bleeding. Symptoms to watch for include bruising or red spots under the skin, red or dark urine, red, black or tarry stools, nosebleeds, or bleeding around the gums after gentle tooth brushing. Internal hemorrhaging may manifest itself in a variety of ways, including pain in joints, chest, stomach or head. Shortness of breath, difficulty breathing or unexplained swelling could indicate bleeding. Alert your physician immediately if you notice any unusual symptoms or signs of spontaneous bleeding.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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