News Release

Research suggests no difference in morning versus evening dosing for warfarin

The effect of warfarin administration time on anticoagulation stability (INRange): A pragmatic randomized controlled trial

Peer-Reviewed Publication

American Academy of Family Physicians

Patients taking warfarin to reduce the risk of stroke and pulmonary embolisms are often advised to take the medication in the evening. But does time of day really matter? A new study shows evidence that morning versus evening dosing has insignificant bearing on how long the drug provides the most benefit for preventing adverse health events. Two hundred and seventeen adults who regularly used warfarin in the evenings were randomized to the trial, with about half switching to morning medication use for seven months. Researchers measured the effectiveness of the drug by tracking the proportion of time that patients spent outside of the range for maximum effectiveness of the drug. Therapeutic changes did not significantly differ for patients who switched to morning administration. The clinical research team concluded that the time of day a patient takes the medicine has no effect on the stability of warfarin's anticoagulant effect. Patients should take warfarin whenever regular compliance would be easiest.


The Effect of Warfarin Administration Time on Anticoagulation Stability (INRange): A Pragmatic Randomized Controlled Trial
Scott R. Garrison MD, PhD, et al
University of Alberta, Department of Family Medicine, Edmonton, Alberta, Canada

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