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®.
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.
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
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).
