The People's Perspective on Medicine

Can You Stay in the Sweet Spot for Your Warfarin Dose?

It can be difficult to get the warfarin dose just right all the time. Even people who managed it most of the time sometimes had a dangerous deviation.

Warfarin is a classic anticoagulant that is used to prevent strokes and deep vein blood clots. Doctors know a lot about this old inexpensive drug, but they also know getting the warfarin dose just right can be difficult to manage.

Managing the Warfarin Dose Balancing Act:

Physicians at Duke University Medical Center studied the records of more than 3,700 people on warfarin. They analyzed the INR (International Normalized Ratio) values, a measurement of how well warfarin is blocking blood clotting.

Just about one-fourth of the patients in this group had at least 80 percent of their INR values within range during the first six months. About one-third of those continued to have at least 80 percent of their INR values in range for the rest of the year. For most of these patients, the target INR range was between 2 and 3.

Staying in Range Is Tricky:

Unfortunately, however, at least 36 percent of them had at least one INR reading that was far out of range during that time. A high reading signals the risk of a dangerous bleeding episode, while a low reading points to the possibility of a disabling clot.

The investigators conclude that warfarin dose stability is difficult to predict. The fact that warfarin interacts easily with many other medications as well as foods and beverages probably contributes to this problem.

JAMA, Aug. 9, 2016 

What About Other Options?

These researchers are enthusiastic about newer anticoagulants that have fewer interactions with food and do not require (or even accommodate) dosing adjustments. As a consequence, drugs such as apixaban (Eliquis), dabigatran (Pradaxa), edoxaban (Lixiama) or rivaroxaban (Xarelto) may be easier for physicians to use, but it is not yet clear that they are better for patients. They are far more expensive, and not all of them can be easily reversed if the patient starts to bleed excessively.

People faced with the need for an anticoagulant long term should have a serious discussion with the prescribing physician and participate in shared decision making. (This Medscape article has a clear explanation. Those who cannot access Medscape may also appreciate this article in Circulation, Nov. 25, 2014.) Also see Hematology, 2013

You can learn more about foods and drugs that interact with warfarin from our free Guide to Coumadin Interactions.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies. .
Coumadin Interactions
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The key to keeping the warfarin INR values within range is to stick CONSISTENTLY to your same diet. If you eat a lot of vitamin K-containing foods, then don’t change the amounts consumed erratically.

I have been on warfarin for 7 years now and do not have an issue keeping my INR between 2.1 and 2.6. I eat a whole lot of greens every week and at least one to two helpings every day as a means of regulating my body’s absorption of warfarin. I know several friends that won’t eat a salad, garden peas, or any greens “because I’m on Coumadin” and somewhere have either misunderstood a health professional’s suggestions or gotten confused by other sources of information about the interaction of vitamin-K foods and warfarin.

Several things that I don’t do is to drink a lot of green tea because it has a high concentration of vitamin K, eat more than a tablespoon of collards, or more than 10 spinach leaves. Otherwise, I don’t consciously worry about my INR getting too high, so long as I eat greens every day.

My husband has been on Warfarin for several years. Normally there’s no problem. However, a while back his numbers were off the charts. His dosage was adjusted but the numbers were more or less out of control. This went on for about 3 months with no explanation. We finally figured the mail order facility probably changed to a less reliable manufacturer because all of the sudden numbers went back to where they’d been and have stayed that way.

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