Why does warfarin need to be monitored?

When trying to decide which testing device or IDTF service to use, you may want to consider:

• The advice or recommendation of your physician or anticoagulation clinic, based on their experience and knowledge.
• The experience of other patients and their satisfaction with their home monitoring device and the educational and support services provided to them by the manufacturer and/or distributor.
• The amount of blood needed for the test strip.
• Ease of use associated with operating the instrument or testing device.
• Weight of the instrument may matter to you, especially if you travel frequently.

If you are on warfarin and are interested in checking your INR with a home monitoring device, you should discuss your options with your healthcare provider. Your healthcare provider will need to 1) write a prescription for the device 2) be available to instruct you in dosage adjustments and 3) remain medically responsible for your anticoagulation management.Once a prescription has been written that directs you to self-test your INR, you can speak with your doctor or your insurance company for guidance about where to obtain your device and how to get started.

You also can get similar guidance from a POC device manufacturer or an Independent Diagnostic Testing Facility (IDTF) or distributor that provides patient services connected to at-home INR testing. Most of these IDTFs will require that your doctor send them your self-testing prescription, as well as your relevant medical information, to enroll you in their service.

IDTFs can play a valuable role in your self-testing efforts, as they can help you verify your insurance or Medicare coverage, provide training to help improve your self-testing skills, help manage your testing results, and ensure that your test results routinely reach your healthcare professional.

Below is an alphabetical listing of several different device manufacturers, IDTFs, and patient services that you can explore for more information and guidance:

Acelis Connected Health

Acelis Connected Health, an Abbott Company, provides an end-to-and service for PT/INR management with support for both patients and their physicians. You can learn more about Acelis Connected Health and their service by reading the frequently asked questions that appear on their website here.

Advanced Cardio Services

Advanced Cardio Services is an IDTF that provides a home anticoagulation testing and monitoring service to help reduce the risk of potential complications associated with long-term warfarin therapy or out-of-range INR levels. You can learn more about INR self-testing through this service by reading the frequently asked questions that appear on their website here.

CoaguChek® and CoaguChek® Patient Services

CoaguChek® and CoaguChek® Patient Services is a service of Roche Diagnostics. Roche Diagnostics manufactures and sells a broad spectrum of diagnostic equipment and supplies, including the CoaguChek® XS device for INR self-testing. To learn more about this company’s INR self-testing devices and patient home-testing services, you can begin by reading the information that appears on their CoaguChek® Patient Services website here.

mdINR

mdINR is a Lincare company, and an IDTF that provides equipment and services for patients who perform INR at-home self-testing. You can learn more about their services by reviewing the frequently asked questions posted to their website here.

RCS (Remote Cardiac Services)

RCS is an IDTF that supports the INR self-testing needs of clinicians and patients. You can learn more about INR self-testing through this service by reading the frequently asked questions that appear on their website here.

Remote INR™ by BioTel® Heart

Remote INR™ by BioTel Heart® (formerly CoaguChek® Patient Services) provides the convenience and quality to implement a successful self-testing anticoagulation program for patients and physicians. For more information about this company’s patient home-testing services, and to review the frequently asked questions that appear on their website, click here.

Warfarin (brand names Coumadin 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 heart attack, stroke, deep vein thrombosis or pulmonary embolism. Because warfarin interferes with the formation of blood clots, it is called an anticoagulant (PDF). 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 protime (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 (see graphic below).

Difference Between Brand-Name and Generic Medications

Generic drugs are supposed to have the same dosage, therapeutic effects, route of administration, side effects, and strength as the original drug. The U.S. Food and Drug Administration requires that all generic drugs be as safe and effective as brand-name drugs.

Generic drugs are often less expensive than their brand-name counterparts, because the generic manufacturers have not incurred the expenses of developing and marketing a new drug. In the United States, trademark laws do not allow generic drugs to look exactly like the brand-name drug; however, the generic drug must have the same active ingredients. In the case of Coumadin (a brand-name product) and warfarin (a generic product), the manufacturers attempted to keep the colors consistent with the strength of the pills. The goal is to allow the patient to identify the color-coded dose and prevent mix-ups or errors. Therefore, if the color or dose of the dispensed tablet appears different from the pill taken previously, the patient should immediately notify the dispensing pharmacist or healthcare provider.

In 2006, the Food and Drug Administration issued a public health advisory to healthcare professionals and consumers that U.S. prescriptions filled abroad may give patients the wrong active ingredient for treating their health condition. Some FDA–approved products have the same brand names as drug products marketed outside the United States but contain completely different active ingredients. Therefore, patients who fill U.S. prescriptions abroad, either when traveling or online, need to maintain caution and vigilance. We advise U.S. residents against purchasing drugs at foreign Internet pharmacies. Foreign drugs may use identical or potentially confusing brand names for products with active ingredients that differ from U.S. drugs. Warfarin has many foreign brand names (Table 1). Patients who do fill prescriptions abroad should ensure the accuracy and quality of the medication dispensed.

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 forgotten, call your healthcare provider for advice.

Foreign Brand Names for Warfarin

Side Effects

The major complications associated with warfarin are clotting due to underdosing 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:

• Severe headache, confusion, weakness or numbness
• Coughing up large amounts of bright red blood
• Vomiting blood
• Bleeding that will not stop
• Bright red blood in stool
• Fall or injury to the head
• Headache that is severe or unusual

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

• Use a soft-bristle toothbrush
• Floss with waxed floss rather than unwaxed floss
• Shave with an electric razor rather than a blade
• Take care when using sharp objects, such as knives and scissors
• 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.

Common Do's and Don'ts

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 (brand name Advil) and naproxen (brand name Aleve), 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. This means an average of one to two drinks per day for men and one drink per day for women. (A drink is one 12 oz. beer, 4 oz. of wine, 1.5 oz. of 80-proof spirits, or 1 oz. of 100-proof spirits). 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. Download our quick reference guide to foods that are high and low in Vitamin K. (PDF)

Wear Medical Identification

Those who require long-term warfarin should wear a medical alert bracelet, necklace, or similar alert tag at all times. If an accident occurs and the person is too ill to communicate, a medical alert tag will help responders provide appropriate care. The alert should include a list of major medical conditions and the reason warfarin is needed, as well as the name and phone number of an emergency contact.

Where to Get More Information

Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no 2 patients are exactly alike, and recommendations can vary from 1 person to another, it is important to seek guidance from a provider who is familiar with your individual condition.