Warfarin, a vitamin-K antagonist, exerts its anticoagulant effects by inhibiting the production of vitamin K-dependent clotting factors.(1) Warfarin is monitored by the international normalized ratio (INR), a standardized measure of prothrombin time, which is used to determine the clotting tendency of the blood.(2) Warfarin is a high-risk medication due to its narrow therapeutic index. Subtherapeutic levels increase the risk of thromboembolism while supratherapeutic levels increase the risk of hemorrhage. The metabolism of warfarin is affected by various prescription, over-the-counter, and botanical medications, food, genetic variations, and diseases.(1)
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