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Warfarin and other VKAs: Dosing and adverse effects

Russell D Hull, MBBS, MSc
David A Garcia, MD
Section Editor
Lawrence LK Leung, MD
Deputy Editor
Jennifer S Tirnauer, MD


Warfarin and other vitamin K antagonists (VKAs, also called coumarins; eg, acenocoumarol, phenprocoumon, fluindione) are used in a variety of clinical settings. Their use is challenging because their therapeutic range is narrow and dosing is affected by many factors including genetic variation, drug interactions, and diet. Time spent with a prothrombin time (PT)/international normalized ratio (INR) above the therapeutic range increases the risk of bleeding, and time spent below the therapeutic range increases the risk of thromboembolic complications, which these agents were administered to prevent. Nevertheless, these agents have a large body of clinical experience and are highly effective in reducing the risk of venous and arterial thromboemboli in many settings.

The general principles underlying the clinical use of VKAs, including their complications and laboratory monitoring, will be reviewed here.

Management of bleeding or supratherapeutic INR in patients receiving warfarin is discussed separately. (See "Management of warfarin-associated bleeding or supratherapeutic INR" and "Reversal of anticoagulation in warfarin-associated intracerebral hemorrhage".)


Indications for vitamin K antagonists (VKAs) are presented in separate topic reviews:

Atrial fibrillation – (See "Atrial fibrillation: Anticoagulant therapy to prevent embolization".)


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Literature review current through: Sep 2016. | This topic last updated: May 31, 2016.
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