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What Is Warfarin?

Warfarin is the generic version of an anticoagulant (blood thinner) medicine that helps stop blood clots from forming. If blood clots do form, warfarin can keep them from growing larger. Warfarin is often called a “blood thinner,” but it does not thin your blood. Instead, it makes your blood take longer to clot.

What Is Warfarin Used For?

Warfarin prevents blood clots from forming inside your blood vessels or heart. The medication also keeps existing clots from getting larger and may stop existing clots from breaking off and traveling elsewhere in your body. Your provider may prescribe warfarin if you have a blood clot or are at risk for developing a blood clot.

Providers also prescribe warfarin for other conditions, such as the following:

How Does Warfarin Work?

Your liver uses vitamin K to make proteins called clotting factors. They make your blood clot when you’re cut or injured. Warfarin prevents your liver from using vitamin K. Therefore, you don’t have as many clotting factors, and your blood takes longer to clot.

Warfarin does not dissolve clots. Instead, it keeps them from getting bigger. Your body will break down the clot naturally over time. Warfarin also helps reduce the risk of new clots.

Eliquis vs. Warfarin

Warfarin is a long-acting medication. You will need to take it for several days before it slows your blood’s clotting ability. Eliquis is a faster-acting medicine and becomes effective within 24 hours. Instead of blocking vitamin K, Eliquis blocks an enzyme that encourages blood clotting. Your provider will recommend a medication based on your symptoms and condition.

How Is Warfarin Administered?

You take warfarin as a tablet. The tablets come in various shapes, and the color indicates the strength of the dose. For example, 1 milligram tablets are pink, 5 mg tablets are peach, and 10 mg tablets are white. All drug manufacturers use these color guidelines.

If you have swallowing difficulties, you may crush warfarin tablets. Mix the powder with water or soft food before eating it.

Warfarin & INR

You won’t be able to tell if warfarin is working based on how you feel. Instead, your provider will use a blood test to determine how effective the medicine is. The International Normalized Ratio (INR) measures how long your blood takes to clot and is a way to measure the effect of warfarin. Your provider will use your INR blood test to adjust your dose if necessary.

When you start taking warfarin, you’ll have an INR test at least twice a week. Eventually, you will be able to test less frequently. However, you may need additional testing if you have changes in your medications, diet, or overall health condition.

Normal INR on Warfarin

Before someone starts warfarin, the INR is usually around 1.0. While everyone is different, most people should have an INR between 2 and 3. This means it takes 2–3 times longer for your blood to clot than if you weren’t taking warfarin.

How to Adjust Warfarin Dose Based on INR

Your INR can change for many reasons. If it’s too high, you are at risk of excessive bleeding. If it’s too low, you could develop new blood clots. Some people change their warfarin dose on their own using INR results provided by a lab. However, most people report INR results to their provider, who will recommend a dosage change to achieve their goal.

What Is a Dangerous INR Level on Warfarin?

Any INR above your goal range increases your risk of bleeding problems. If your INR is high, your provider may have you stop taking warfarin temporarily or eat foods high in vitamin K, like leafy green vegetables, to adjust your level.

Warfarin Diet

Foods that include vitamin K can counteract warfarin’s effectiveness. While you don’t have to stop eating these foods, you should try to eat the same amount each week. In fact, a consistent amount of Vitamin K in the diet could actually help keep the INR level stable. Sudden changes in your diet could spark a change in your INR. This means if you have more dietary Vitamin K your INR could go down, and if you have less dietary Vitamin K your INR could go up.

Foods that contain high amounts of vitamin K include the following:

  • Broccoli
  • Cabbage
  • Greens (collard, mustard, turnip)
  • Kale
  • Spinach

Be sure to read labels, as some processed foods contain added vitamin K. Meal replacement products like Boost, Ensure, Premier, Carnation Instant Breakfast, and SlimFast may contain high amounts of vitamin K.

Warfarin Side Effects

Many people take warfarin for years with no complications. Bleeding is the most common side effect of warfarin. While taking warfarin, you may experience certain side effects:

  • Bleeding gums when you brush your teeth
  • Bleeding longer if you cut yourself
  • Easy bruising
  • Menstrual periods that are heavier or longer than usual
  • Nosebleeds

Serious side effects that require medical attention include:

  • Bleeding from a cut that won’t stop even after applying pressure
  • Blood in urine or stool
  • Bruises that appear for no reason or become large and painful
  • Nosebleeds that last longer than 10 minutes
  • Numbness in your arms or legs
  • Severe headache
  • Sudden loss of vision or blurred vision

Why Choose University of Utah Health?

Our Thrombosis Service helps you monitor and manage your warfarin dose. Expert pharmacists and internal medicine doctors recommend dose adjustments based on your INR. We are also an Anticoagulation Center of Excellence and offer patients the highest level of care.

How to Refer a Patient to the Thrombosis Clinic

U of U Health providers can refer patients to the Thrombosis Service. Send referrals via the patient’s electronic health record. To learn more, please call 801-213-9150.