Medication Safety: Blood Thinners
Coumadin and other blood thinners are life-saving medications. Here are things you should know about this treatment.

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Picture of pharmacist looking at prescription bottle Medication Safety: Blood Thinners

There are many possible reasons your doctor might prescribe an anticoagulant or blood thinner.

You may be at risk for a blood clot if you have had a heart attack or stroke, or have atrial fibrillation or heart valve replacement.

You may need to take blood thinners if you've just had surgery or if you've recently had a blood clot in your leg (deep vein thrombosis, or DVT), or your lung (pulmonary embolism).

Blood's ability to clot is a normal and necessary body process. Clotting keeps you from bleeding too much if you are injured. But sometimes your blood clots too easily or a clot doesn't break down normally. Blood clotting problems can be inherited (genetic) or be due to another condition, such as cancer.

Use of blood thinners is often life-saving and is needed to prevent serious health complications, but it can also have significant risks. Since blood thinners affect your blood's ability to clot, it will usually take longer for the blood to form a clot. Although this effect is critical to prevent life-threatening blood clots, it can also leave you at risk for bleeding too much.

To assure your safety while taking blood thinners, you must be careful to avoid injury and, when appropriate, get frequent blood tests to monitor the effect of the blood thinner on your blood. It is important to note that not all blood thinners require frequent blood testing.

How do blood thinners work?
Blood thinners work by blocking substances, such as clotting factors, and other substances in the blood that are needed to form a clot. This keeps new clots from forming and existing clots from getting bigger. Even though they are sometimes called blood thinners, they do not actually thin the blood.

Warfarin and heparin are the two main anticoagulant medicines. You take warfarin (Coumadin) as a pill. Heparin is given intravenously (through the vein) or as a shot. Both require close monitoring with blood tests. However, a number of new medications are coming on the market which do not require the kind of monitoring that is needed for warfarin.

What kind of monitoring do I need?
If you take warfarin (Coumadin), you need to a have test called prothrombin (pro-time or PT). The results of the test are usually reported as an "INR" (international normalized ratio). This is a method to make results standard among labs using different methods.

For this test, a small sample of blood is taken and tested to see how long it takes your blood to clot. Your doctor may adjust your dose of blood thinners based on these results.

When you first start taking warfarin, you may need a daily test as your doctor adjusts your dose. Once a target INR is reached, less frequent testing will usually be needed.

How long will I need to take warfarin?
How long you take anticoagulants depends on the reason for its use and your overall condition. For example, if you have a genetic blood clotting disorder or an ongoing risk for heart attack or stroke, you may need to take them for the rest of your life. In other cases, you may take an anticoagulant after surgery for a period of days or weeks.

In some cases, doctors use other drugs called antiplatelet drugs to help prevent the risk of clots. These drugs include aspirin, dipyridamole (Persantine) or clopidogrel (Plavix). They block platelets, which are needed to form clots. These medicines don't require as much monitoring as warfarin or heparin, but they don't work as well to prevent clots. A number of new anticoagulants are being studied, and a few, such as dabigitran (Pradaxa) and rivaroxaban (Xarelto), have come on the market that don't require the close monitoring that is needed for warfarin. The medical community is currently in the process of learning how to best use these new medications.

Do anticoagulants interact with other medications?
Many other medications, vitamins and herbal supplements can interact with anticoagulants. It's especially important not to take aspirin or medicine that contains aspirin while on an anticoagulant, unless specifically recommended by your doctor.

Tell your doctor about all the prescription and over-the-counter medicines, vitamins and herbal supplements you take. It may help to make a list and bring it with you when you see your doctor.

Do I need to change my diet?
Foods that contain vitamin K are a special concern if you are taking warfarin. Beef, pork liver, broccoli, kale, spinach and other leafy greens, chickpeas, green tea and soybean products can work against the warfarin.

Talk to your doctor about your diet before you take warfarin. You may be able to keep eating these foods as long as you are consistent in how much you consume day to day. Don't make any major changes in your diet after you start the warfarin.

What activities should I avoid?
Be very careful to avoid getting cut when you use a knife or scissors. Avoid contact sports or recreational activities that may lead to bruising or other injury, especially head injury. Doctors also suggest using an electric razor instead of a razor blade, and soft toothbrushes. Report any unusual bleeding to your doctor right away.

Illness can also interfere with your Coumadin/warfarin therapy. If you have fever or the flu, call your doctor. Also contact your doctor if you develop diarrhea.
By Louis Neipris, MD, Contributing Writer
Created on 01/09/2009
Updated on 06/01/2012
  • American Society of Hematology. Blood detectives discussion guide.
  • American Heart Association. What are anticoagulants and antiplatelet agents?
  • American Heart Association. Anticoagulation
  • Agency for Healthcare Research and Quality. Blood thinner pills: Your guide to using them safely.
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