The goal of anticoagulation therapy with warfarin () is to decrease the clotting ability of your blood so that blood clots are prevented. The most important aspect of warfarin therapy is to keep your levels within a therapeutic range. If your level goes too low, you are at risk for blood clots; if it goes too high, you’re at risk for bleeding. Many factors can affect your level. In order to provide you with the safest and most effective therapy, your health care provider needs you to act as a partner in your care. Your role is to gain knowledge about your therapy and the factors that affect it, and then use this information in your daily activities. This guide is to empower you with that information. If you have any questions or concerns about your warfarin therapy after reading this guide, please speak with your health care provider.
Warfarin (Coumadin®) is an anticoagulant. means against, and refers to blood clotting. Warfarin reduces the body’s ability to make blood clots. Your health care provider wants you to take warfarin because your body may make clots that you don’t need. These clots can cause a serious medical problem. A clot can move to another part of your body. For example, if a clot moves to your brain, it can cause a stroke.
The most common reasons for taking warfarin (Coumadin®) include:
- This is a blood clot that occurs in a deep vein. They most often occur in the legs, but can occur in other parts of your body as well.
- This is a blood clot in the lung. Most often, the blood clot starts in the leg, breaks off and travels to the lung.
- These are irregular heart rhythms that occur in the upper chambers of the heart (the atria). The atria do not empty all of the blood, which can cause the leftover blood to form clots. If a clot goes into your circulation, it can cause a stroke.
- Blood clots can form on the mechanical heart valve. If a clot forms on the valve, it can prevent the valve from functioning; or if the clot breaks off into your circulation, it can cause a stroke. People with mechanical heart valve replacements must be on warfarin therapy for life.
- Sometimes warfarin is taken after a heart attack to lower the risk of death, another heart attack or stroke.
- If a stroke is caused by a blood clot going to the brain, warfarin is used to prevent it from recurring.
- Warfarin is given to prevent a stroke from occurring.
- Some surgical procedures place a person at high risk for developing a blood clot (for example, major orthopedic surgery). Warfarin is given temporarily after the surgery to prevent a clot from occurring. Warfarin (Coumadin®) is sometimes given for reasons other than those listed. If you have any questions or don’t understand something in this information, ask your health care provider for more information.
Warfarin (Coumadin®) partially blocks the re-use of vitamin K in your liver. Vitamin K is needed to make clotting factors that help the blood to clot and prevent bleeding. Vitamin K is found naturally in certain foods, such as green leafy vegetables. Warfarin (Coumadin®) reduces the body’s ability to make blood clots. It can help stop harmful clots from forming and keeps clots from getting larger. It does not break up existing blood clots. Warfarin (Coumadin®) begins to reduce blood clotting within 24 hours after taking the drug. The full effect may take 72 to 96 hours. The anti-clotting effects of a single dose of warfarin last 2 to 5 days, but it is important for you to take your dose as prescribed by your health care provider.
Warfarin (Coumadin®) is monitored by a blood test called an INR (International Normalized Ratio).
When your INR falls within your range (for example, between 2.0 and 3.0), this means that your level is “therapeutic.” When your INR level goes below the range (for example, 1.5) this means your blood is “too thick,” and places you at risk for blood clots. In this situation, your health care provider will prescribe a higher dose of warfarin for you. If your INR goes above your range (for example, 4.5) this means your blood is “too thin,” and places you at risk for bleeding. In this situation, your health care provider will prescribe a lower dose of warfarin.
Because warfarin (Coumadin®) affects each person differently, some people will be on small doses of warfarin and some will be on very large doses. Some people will achieve their appropriate INR quickly and others more slowly. Many factors can affect your INR level including a change in diet, a change in medications, the onset of a new illness or having to stop your warfarin for a procedure.
When you first start taking warfarin (Coumadin®) the INR level tends to fluctuate up and down until the correct dose is found that keeps your INR level stable. It is therefore to get your INR level checked frequently. In general, when you first start warfarin you will need to get your INR level checked 2 to 3 times a week for the first two weeks, then one to two times a week for two weeks, then every other week, and then once a month. This may vary, depending on how your INR levels are. If the INR level becomes stable quickly, you will go for blood tests less often; if the INR level does not become stable, you will need to go for blood tests more often.
When your INR level is too high or too low, you often will not feel any symptoms. This is why it is to get your INR blood tests done regularly!
Warfarin belongs to a category of drugs known as “narrow range of effectiveness” drugs. This means that there is a very narrow range where the drug is considered therapeutic. For most indications, the INR range is 2.0 to 3.0. For people with mechanical heart valve replacements and certain other conditions, the range is 2.5 to 3.5. These ranges are general recommendations. Your health care provider might prescribe a different range, depending on your particular condition.
Warfarin (Coumadin®) interacts with of drugs including prescription and non-prescription (over-the-counter) drugs. Drug interactions can cause your INR to go too high (placing you at risk for bleeding) or cause your INR to go too low (placing you at risk for blood clots). Examples of some drugs that interact with warfarin are given below. The list is by no means all-inclusive. It is just to give you an idea of some of the more common drugs that interact with warfarin. It is for you to check with your health care provider before starting, changing or stopping any drug, whether it be prescription or over-the-counter. If you need to be on a medicine that is known to interact with warfarin, it does not mean that you cannot take it. It does mean that you will need to get your INR monitored more closely when you start the new medicine.
· Anti-platelet drugs (such as Plavix®, Ticlid®)
· Diabetes drugs
· Gastrointestinal drugs
· Gout treatment drugs
· Lipid-lowering drugs
· Thyroid drugs
· Antifungal drugs
· Cimetidine (Tagamet)®
· Ranitidine (Zantac)®
· Vitamin C (Greater than 500 mg per day)
· Vitamin E (Greater than 400 IU per day)
· Multivitamins containing Vitamin K
· Glucosamine & Chondroitin
· Coenzyme Q10
Herbal medicines can also cause dangerous drug interactions with warfarin (Coumadin®). Keep in mind that just because an herbal product is advertised to be does not necessarily mean it is . Below is a list of herbal products known to interact with warfarin. The list is not all-inclusive. If you want to take an herbal supplement, it is that you contact your health care provider before taking it.
· Aloe Gel
· Aniseed Angelica (Dong Quai)
· Asa Foetida
· Bladder Wrack (Fucus)
· Black Cohosh
· Black Haw
· Buchu Boldo
· Chamomile (German & Roman)
· German Sarsaparilla
· Ginkgo Biloba
· Green Tea
· Passion Flower
· Pau d’arco
· Red Clover
· St. John’s Wort
· Sweet Clover
· Sweet Woodruff
· Tonka Beans
· Wild Carrot
· Wild Lettuce
Warfarin (Coumadin®) interacts with vitamin K in your diet. Vitamin K is necessary in the blood clotting process. Food sources with the highest amount of vitamin K include dark green leafy vegetables. These foods are heart healthy, they are high in lutein, which improves vision, and high in fiber, which is good for the gastrointestinal tract. The recommendation is to keep your diet . This means that you should eat the same amount of vegetables from week to week. Do not eat many dark green leafy vegetables one week, and then none the following week. As long as you maintain a consistent amount of vitamin K in your diet, the warfarin will balance with it. If your vitamin K intake fluctuates, your INR level will fluctuate. Remember, just because a vegetable is green does not mean it is high in vitamin K. It is only the green leafy vegetables that are high in vitamin K.
· Greens (collard greens, turnip greens, mustard greens)
· Lettuce (except iceberg lettuce, which is low in vitamin K)
· Brussels sprouts
· Cauliflower (although it is white, it is in the same family as broccoli)
· Green beans
Many dietary supplements contain vitamin K. Examples of these products include Ensure, Boost and Carnation Instant Breakfast. The fact that these products contain vitamin K does not mean you should not use them. As with diet, keep your vitamin K intake consistent. If you have never used these products but would like to start, contact your health care provider. You will need to get your INR level monitored more closely when you start them.
Which vitamins are safe to take when you are taking warfarin (Coumadin®)? Below is a list of some of the most common vitamins and their effect on the INR level:
- No effect on the INR level
- Up to 500 mg per day will have no effect on the INR. Doses greater than 500 mg may lower the INR level
- Up to 400 IU per day will have no effect on the INR. Doses above 400 IU may increase the INR level
- Most multivitamins contain small amounts of vitamin K. It is OK to take them, but as with diet, be consistent in taking them every day to prevent your vitamin K intake from fluctuating. If you are not using multivitamins but would like to start, contact your health care provider. You will need to get your INR level monitored more closely when you start them.
alcohol in moderation (up to 2 drinks per day) will have little effect on the INR level. Excess alcohol intake will elevate the INR level because both the alcohol and the warfarin (Coumadin®) are metabolized through the liver. If you have a problem with excessive alcohol intake and are taking warfarin, please speak with your health care provider. This lethal combination may place you at serious risk of a bleeding event.
The most serious side effect of warfarin (Coumadin®) is bleeding. To lower the risk of bleeding, be sure to get your INR level monitored regularly. Monitor yourself for:
- Bleeding of gums when you brush your teeth
- Vomiting blood
- Blood in your urine
- Bowel movements that look red or black
- Unusual bruising
- Cuts that do not stop bleeding
- Excessive bleeding when you get your menstrual period or unexpected bleeding from the vagina
- Headache, dizziness or weakness
- Unusual pain or swelling
If you develop bleeding (for example, a nosebleed or bleeding from the gums that stops within a few minutes) contact your health care provider. You will need to get your INR level checked.
If you develop bleeding (for example, vomiting blood or a nosebleed that won’t stop) . This could be a sign of a serious problem.
If you are involved in any kind of (for example, a car accident or falling down and hitting your head on the pavement), . You will need to be checked for internal bleeding.
- Hair loss: Hair loss is an infrequent side effect of warfarin therapy and is reversible.
- Rash: If you develop a rash after starting warfarin therapy, notify your health care provider.
- Pregnancy: If you become pregnant or are planning to become pregnant, notify your health care provider. Warfarin (Coumadin®) is dangerous to the unborn baby and should not be taken during pregnancy.
- Avoid any activity or sport that may result in a traumatic injury.
- You may find that if you get a cut or scratch it may bleed longer than when you were not taking warfarin. Just apply pressure to the area. It should stop within a few minutes.
- You may find that you bruise easier than when you were not on warfarin. Try to be careful!
Adapted from: Your Guide to Coumadin®/Warfarin Therapy, AHRQ Pub. No. 08-0028-A Revised August 2008.