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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 TipsThe 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 MedicationsGeneric 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 EffectsThe 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:
An unusual headache or a headache that is more severe than usual may signal intracerebral bleeding. When to Call Your Healthcare ProviderIf you experience the following signs of bleeding, you should call 911 or your healthcare provider immediately:
Some simple changes to decrease the risk of bleeding while taking warfarin include the following:
Warfarin and LifestyleChanges in daily living can affect the INR. It is important to know common do’s and don’ts for warfarin therapy. PregnancyWarfarin 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 ProceduresIt 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. TravelCheck 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 MedicationsPatients 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
Wear Medical IdentificationThose 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 InformationYour 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. Written by American Heart Association editorial staff and reviewed by science and medicine advisers. See our editorial policies and staff. Which of the following laboratory values should the nurse monitor for a therapeutic effect of warfarin?International normalized ratio (INR) Rationale: The INR is used to monitor clients who are taking warfarin. Which adverse effect would the nurse include in teaching the client about niacin?Flushing. Flushing (warmth, redness, itching and/or tingling of the skin) is a common side effect of niacin therapy that may subside after several weeks of consistent NIASPAN use. Which of the following laboratory values should the nurse monitor for a therapeutic effect of warfarin?International normalized ratio (INR) Rationale: The INR is used to monitor clients who are taking warfarin.
Which adverse effect would the nurse include in teaching the client about niacin?Flushing. Flushing (warmth, redness, itching and/or tingling of the skin) is a common side effect of niacin therapy that may subside after several weeks of consistent NIASPAN use.
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