Warfarin (Coumadin) to Prevent Strokes

Warfarin (Coumadin®) is an anticoagulant medication that interferes with the blood’s ability to clot. It is often called a “blood thinner” and is frequently prescribed for people with atrial fibrillation to prevent a stroke.1

Warfarin is the oldest oral anticoagulant available, with more than 50 years of studies attesting to its effectiveness and safety. Discovered in the 1940s by a scientist at the University of Wisconsin-Madison, it was originally used as a rat poison. It was approved as a medication in 1954 and is now widely prescribed for preventing strokes from atrial fibrillation.1

Warfarin is generally recommended for those with valvular afib (defined as a mechanical heart valve or moderate-to-severe mitral stenosis) due to direct oral anticoagulants not being well studied for those with valvular afib.2,3

Other names for warfarin include Jantoven®, Marevan®, Lawarin®, Waran®, and Warfant®.

How It Works

Your body needs vitamin K to form blood clots. Warfarin works by blocking this action, thus preventing clots that could cause a stroke. For this reason, warfarin is often referred to as a Vitamin K antagonist.

Dosage and Testing

 Unlike most drugs, there is no one-size-fits-all dose for warfarin. Instead, your doctor will decide your dose based on how you respond to it. To do so, you will have regular tests to determine how fast your blood will clot based on a scale called the International Normalized Ratio (INR). Then, your dosage will be adjusted as needed.

Ideally, afib patients should maintain an INR of between 2.0 and 3.0 (this will vary for those who have had valve replacement). Any lower, and warfarin may not prevent clots; any higher and you may have an increased risk of bleeding.

Depending on how stable your INR levels are, you will have testing done anywhere from weekly to monthly. Initially, you may have weekly INR testing; once your INR levels are stable, you may move to monthly INR testing.3

Today, testing can be done in a clinic, through a blood draw or a finger stick, or at home with a simple finger stick, much like people with diabetes test their blood sugar levels. An analysis of 22 home monitoring studies found that people were better at tracking their INR when they didn’t have to go to a clinic. As a result, the risk of stroke (and similar events) was 42 percent lower than with clinic-based testing with no increased risk of major bleeding. The risk of death also dropped by 26 percent.4

Only a small percentage of people on warfarin use home testing, yet experts say eight out of ten can use it after some education from their healthcare provider.5,6 Medicare and other insurance companies cover the cost of home testing.4

What to Know If You Take Warfarin

  • Bleeding or Discoloration. All anticoagulants increase the risk of bleeding, so report any signs of unusual bleeding to a healthcare professional immediately. In addition, pain or skin discoloration (a bruise-like rash) or sudden cool, painful, purple discoloration of the toes or front of the foot (indicating blocked blood flow to your feet) should also be reported.7
  • Vitamin K. With warfarin, take care when eating foods high in vitamin K, particularly green leafy vegetables. Doctors suggest keeping your daily intake of Vitamin K consistent so it doesn’t interfere with warfarin’s anti-clotting abilities. Vitamin K can be found in more than 1,000 foods, so there are apps and sites for tracking your vitamin K intake (search “INR tracking”). Also, limit cranberry and grapefruit intake as they can affect how well warfarin works.5
  • Medications and herbal supplements. Many common medicines, including antibiotics and some anti-anxiety medications, interact with warfarin. Herbal supplements, including ginseng, ginkgo biloba, ginger, garlic, and St. John’s wort, also interact with it. Even aspirin can be a problem. Healthcare professionals, including your pharmacist, can help you avoid potentially dangerous medication interactions.
  • Genetics. Many genes are involved in how the body metabolizes warfarin. Some people have a low tolerance for a drug, so their body takes longer to break it down, and it remains in their system longer. This is often due to certain genetic mutations. Your doctor can give you a genetic test before starting warfarin to see how you may respond to it.8
  • Activities. You may need to avoid activities or sports that could lead to injuries and take great care with activities that could lead to cuts or bleeds that may be difficult to stop. Also, let your doctor know if you have a fall as it could cause internal bleeding. Those on warfarin may also bruise easily.
  • Medical IDs. Since warfarin increases your risk of bleeding, consider wearing a medical ID to alert people that you take warfarin.
  • Surgery and procedures. It’s important to let your doctor and dentist know that you’re taking warfarin as it may increase bleeding during any kind of surgical or dental procedure. If you need surgery, your doctor may ask you to discontinue warfarin a few days before surgery to reduce the risk of uncontrolled bleeding. For emergency surgery or severe bleeding, reversal agents may be used to quickly stop the anti-clotting effects of warfarin.

A Personal Note from Mellanie

As you learned from this section, not everyone can take warfarin. Unfortunately, I was one of those who couldn’t. No matter what I did, I just couldn’t keep my INR levels stable, so I was constantly at risk of a clot or  bleeding. I also had severe bruising.

When research showed that about a fourth of people taking warfarin aren’t stable for genetic reasons, I talked with my doctor about options. We decided that a new surgery would be right for me. You can read more about my story.

Learn about the options that can now be used instead of warfarin, called Direct Oral Anticoagulants (DOACs).