Warfarin

Warfarin (Coumadin® and Jantoven®) is an anticoagulant medication or “blood thinner” you take to prevent and treat blood clots that can lead to a stroke or heart attack. Warfarin slows down your blood’s ability to clot. This helps keep unwanted clots from forming inside your blood vessels or heart when you have certain medical conditions or don’t walk or move around for a long time.

If you have a blood clot, warfarin keeps the clot from getting larger. It may also prevent a piece of the clot from breaking off and traveling to your lungs, brain or heart.

How does warfarin work?

Warfarin works by interfering with part of your body’s clot-making process. It stops an enzyme from activating vitamin K. Some of your body’s clotting factors need vitamin K to do their part in the process of making a clot.

How much of the drug warfarin should I take?

Your healthcare provider will prescribe a specific dosage strength. But you may take a different dose based on the results of frequent blood tests. The dose usually ranges from 1 milligram (mg) to 10 mg.

You can buy warfarin as a tablet in many different shapes, sizes and colors. Each tablet color represents a different strength. All companies that make warfarin follow the same color code for the different strengths of their tablets. But the size and shape of the tablets may differ from one company to the next.

Each tablet has its strength stamped on one side. It also has an indent across the tablet so you can break it in half if your provider adjusts your dose.

Warfarin tablets (Coumadin® and Jantoven®)

What is warfarin approved for?

You may take warfarin if you’ve had a blood clot before or if you’re at risk now because you have atrial fibrillation (AFib) or atrial flutter. You may also take it if you had a heart valve replacement.

Warfarin uses include the prevention and/or treatment of blood clots that:

• Are in a vein and then travel elsewhere (venous thromboembolism or VTE)
• Usually happen deep in your leg (deep vein thrombosis or DVT)
• Start in a vein and travel to your lung (pulmonary embolism or PE)
• Block a blood vessel in your brain (stroke)
• Are in the arteries that supply blood to your heart and cause a heart attack
• Are in the left ventricle of your heart
• Are in your arteries due to antiphospholipid syndrome

How should I take this drug?

Instructions for taking warfarin include:

• Take your dose of warfarin once a day at the same time of day.
• Take warfarin before or after eating.
• If you miss a dose, take it as soon as you remember, unless it’s closer to the time of your next scheduled dose.
• Don’t take two doses at the same time unless your healthcare provider tells you to.
• If you forget to take warfarin two or more days in a row, call your provider. They may need to change your dose. (Never change the dose yourself without calling your provider first.)
• Consider using a pillbox to help you remember to take your medication or checking off every day on a calendar after you take your dose.
• Refill your prescription one week before your supply runs out to avoid missing a dose.
• Store warfarin away from heat, moisture or direct sunlight.

What blood tests will I need while I’m on warfarin?

A provider will need to check your blood with a prothrombin time (PT or protime) test. They can use these results to calculate the international normalized ratio (INR). The INR helps a provider monitor how fast your blood is clotting. The results tell them if they need to adjust your dose.

You can get the blood tests at a lab or anticoagulation clinic. You usually need to do the PT test one or more times a week to once a month. Follow your provider’s instructions for how often you need to get blood tests and when to adjust your daily warfarin dose. If you’re planning a trip, talk with your provider about using another lab for your blood tests while traveling.

What can interfere with how warfarin works?

Other medications may increase or decrease warfarin’s anticoagulant effect. You might need to get blood tests more often when you stop, start, increase or decrease the dose of medications that are likely to affect the way warfarin works. You may need a different dose of warfarin, too.

Talk to your healthcare provider who manages your warfarin if you have any changes in your other prescription medications.

Changing your eating habits may mean that you’ll be getting more or less vitamin K in the foods you eat. If you change your eating habits, your provider may want to check your blood more frequently to see how warfarin is working.

You need vitamin K for normal blood clotting. But large changes in the amount of vitamin K in your meals can change the way warfarin works. If you eat foods high in vitamin K (like spinach and leafy greens), it’s important to eat the same amount of these foods from week to week.

Other things that can affect how warfarin works and how well your blood clots include:

• Nonprescription medicines like aspirin or NSAIDs
• Illness
• Herbal products, natural remedies or nutritional supplements
• Grapefruit, pomegranate, mango and cranberry products

What are the side effects of warfarin?

Bleeding is the most common side effect. It can appear as any of several different symptoms. Call your provider if you notice any of the following signs of bleeding:

• More weakness or tiredness than usual, or paleness
• Bleeding from cuts that won’t stop after applying pressure for 10 minutes
• Bleeding from the nose, gums or ears
• Menstrual bleeding (period) that’s heavier or lasts longer than normal
• Unusual color in your pee (dark brown) or poop (red, black or tarry)
• Bruises that appear for unknown reasons
• Blood appearing when you cough or vomit (which may look like coffee grounds)
• Unusual pain, swelling or headache (or severe headache)
• Dizziness or altered mental status
• Stroke symptoms
• Difficulty breathing

How can I lower my bleeding risk while taking this drug?

Ways to limit your bleeding risk while taking warfarin include:

• Be careful when using razors, scissors and knives.
• Avoid climbing to tall heights that could lead to a fall.
• Get medical care right away if you fall or hit your head.
• Use a soft toothbrush. Brush and floss gently to keep your gums from bleeding.
• Check with your provider before starting any sports program or physical activity.
• Talk with your provider if you’re having surgery or dental work.

Does warfarin pass into breast milk?

No, warfarin doesn’t pass into breast milk. You can take warfarin if you breastfeed. Talk with your provider if you become pregnant, are planning to be or want to use birth control.

What’s known about warfarin and overdose?

If you have too much warfarin in your system, your healthcare provider will have you stop taking it. Then, they’ll give you vitamin K (or other blood products). You may receive this by mouth or through an IV in your arm.