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

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.