A Patient’s Guide to Taking Coumadin/Warfarin  

SIR RUN RUN SHAW HOSPITAL SCHOOL OF MEDICINE ZHEJIANG UNIVERSITY

Introduction

Warfarin (brand names Coumadin, Marevan and Jantoven) is a prescription medication used to prevent harmful blood clots from forming or growing larger. Beneficial blood clots prevent or stop bleeding, but harmful blood clots can cause a stroke, heart attack, deep vein thrombosis, or pulmonary embolism. Because warfarin interferes with the formation of blood clots, it is called an anticoagulant. Many people refer to anticoagulants as “blood thinners”; however, warfarin does not thin the blood but instead causes the blood to take longer to form a clot.

How Does Warfarin Work?

The formation of a clot in the body is a complex process that involves multiple substances called clotting factors. Warfarin decreases the body’s ability to form blood clots by blocking the formation of vitamin K–dependent clotting factors. Vitamin K is needed to make clotting factors and prevent bleeding. Therefore, by giving a medication that blocks the clotting factors, your body can stop harmful clots from forming and prevent clots from getting larger.

Monitoring and Dosing Tips

The goal of warfarin therapy is to decrease the clotting tendency of blood, not to prevent clotting completely. Therefore, the effect of warfarin must be monitored carefully with blood testing. On the basis of the results of the blood test, your daily dose of warfarin will be adjusted to keep your clotting time within a target range.

The blood test used to measure the time it takes for blood to clot is referred to as a prothrombin time test, or prothrombin time (PT). The PT is reported as the International Normalized Ratio (INR). The INR is a standardized way of expressing the PT value. The INR ensures that PT results obtained by different laboratories can be compared. It is important to monitor the INR (at least once a month and sometimes as often as twice weekly) to make sure that the level of warfarin remains in the effective range. If the INR is too low, blood clots will not be prevented, but if the INR is too high, there is an increased risk of bleeding. This is why those who take warfarin must have their blood tested so frequently.

Unlike most medications that are administered as a fixed dose, warfarin dosing is adjusted according to the INR blood test results; therefore, the dose usually changes over time. Coumadin/warfarin pills come in different colors, and each color corresponds to a different dose. Warfarin must be taken exactly as prescribed. Never increase or decrease your dose unless instructed to do so by your healthcare provider. If a dose is missed or you take more than intended, call your healthcare provider for advice.

Side Effects

The major complications associated with warfarin are clotting due to under-dosing or bleeding due to excessive anticoagulation. The most serious bleeding is gastrointestinal or intracerebral. Excessive bleeding can occur in any area of the body, and patients taking warfarin should report any falls or accidents, as well as signs or symptoms of bleeding or unusual bruising, to their healthcare provider. Signs of unusual bleeding include bleeding from the gums, blood in the urine, bloody or dark stool, a nosebleed, or vomiting blood. An unusual headache or a headache that is more severe than usual may signal intracerebral bleeding.

When to Call Your Healthcare Provider

If you experience the following signs of bleeding, you should call 911 or your healthcare provider immediately:

Ø  Severe headache, confusion, weakness, or numbness

Ø  Coughing up large amounts of bright red blood

Ø  Vomiting blood

Ø  Bleeding that will not stop

Ø  Bright red blood in stool

Ø  Fall or injury to the head

Ø  Headache that is severe or unusual

Some simple changes to decrease the risk of bleeding while taking warfarin include the following:

Ø  Use a soft-bristle toothbrush

Ø  Floss with waxed floss rather than un-waxed floss

Ø  Shave with an electric razor rather than a blade

Ø  Take care when using sharp objects, such as knives and scissors

Ø  Avoid activities that have a risk of falling or injury (e.g. contact sports)

Warfarin and Lifestyle

Changes in daily living can affect the INR. It is important to know common do’s and don’ts for warfarin therapy

Pregnancy

Warfarin is not recommended during pregnancy. A woman who becomes pregnant or plans to become pregnant while undergoing warfarin therapy should notify her healthcare provider immediately.

Surgery/Dental and Other Medical Procedures

It is important to tell all your healthcare providers that you are taking warfarin. If you are having surgery, dental work, or other medical procedures, you may need to stop taking warfarin.

Travel

Check with your healthcare provider if you expect to travel. While traveling, it is important to carry your medication with you at all times. Do not put medication into checked baggage.

Warfarin Interacts with Other Medications

Patients who take warfarin should consult with their healthcare provider before taking any new medication, including over-the-counter (nonprescription) drugs, herbal medicines, vitamins, or any other products. Many medications can alter the effectiveness of warfarin, resulting in an INR that is either too high or too low. Some of the most common over-the-counter pain relievers, such as ibuprofen (multiple brand names) and naproxen (multiple brand names), enhance the anticoagulant effects of warfarin and increase the likelihood of harmful bleeding.

Warfarin Interacts with Alcohol and with Certain Foods

Alcohol

Alcohol intake can affect how the body metabolizes warfarin. Patients undergoing warfarin therapy should avoid drinking alcohol on a daily basis. Alcohol should be limited to no more than 1 to 2 servings of alcohol occasionally. The antiplatelet effect of alcohol increases the risk of major bleeding, even if the INR remains within the target range.

Foods

Some foods can interfere with the effectiveness of warfarin. The most important point to remember is to eat what you normally eat and not to make any major changes in your diet without contacting your healthcare provider.

Vitamin K

Eating an increased amount of foods rich in vitamin K can lower the PT and INR, making warfarin less effective and potentially increasing the risk of blood clots. Patients who take warfarin should aim to eat a relatively similar amount of vitamin K each week. The highest amount of vitamin K is found in green and leafy vegetables such as broccoli, lettuce, and spinach. It is not necessary to avoid these foods; however, it is important to try to keep the amount of vitamin K you eat consistent.