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Warfarin INR Goals

⭐Test your knowledge and check your answers on the second slide!

Let’s talk warfarin INR goals 🤓⁠

💊 Warfarin is a vitamin K antagonist that requires INR (international normalized ratio) monitoring due to its narrow therapeutic index. Dosing is affected by many factors including diet, drug interactions, genetics, and close INR monitoring is required to decrease the risks of bleeding and/or clotting.⁠

🤔 Overall, direct oral anticoagulants (DOACs) are now recommended over warfarin in the majority of clinical situations unless there is a compelling reason for them to on warfarin such as valvular atrial fibrillation, severe renal dysfunction, patient costs, or close therapeutic anticoagulation monitoring required.⁠

🔑 Key points about INR monitoring:⁠

-Baseline INRs are recommended prior to initiating warfarin therapy⁠
-Warfarin requires overlap or ‘bridging’ with heparin or LMWH for 5 days and until INR is within goal for 24 hours (TIP: warFARin takes a long time to achieve full anticoagulation so think FAR into the future compared to other anticoagulants)⁠
-Changes in the INR is typically seen 2-3 days after administration of the dose (TIP: a physician I use to work with always said Jesus rose on the 3rd day and so will your INR 😅)⁠
-Prior to making a dose adjustment, assess for any missed doses, drug interactions, dietary intake or supplements, documentation of bleeding, or other changes that can affect the INR⁠

How many of the INR goals did you get correct? TIP is to memorize the outlier – the majority of the time, the INR goal is 2-3 except in high-risk patients such as those with mechanical valve replacements in the MITRAL position (goal is higher 2.5-3.5)⁠

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Warfarin Factor Half-Lives

Warfarin is an oral anticoagulant most frequently used to control and prevent thromboembolic events. ACCP recommends that patients newly started on warfarin be bridged with LMWH or unfractionated heparin for 5 days AND until therapeutic INR is achieved. 🌟High-yield fact🌟 The presence of a therapeutic INR does not confer protection from clot formation and expansion during the first few days of warfarin therapy, so if your patient’s INR is 2.0 on day 3, it is recommended to continue bridging until day 5. This recommendation is based on the fact that the anticoagulant activity of warfarin depends on the clearance of functional clotting factors already present in the body. Warfarin works by inhibiting new clotting factors from forming but requires that the old factors be cleared from the body. The clearance of these clotting factors is determined by their half-lives. The earliest changes in the International Normalized Ratio (INR) are typically noted 24 to 36 hours after a dose of warfarin is administered. These changes are due to the clearance of functional factor VII, which is the vitamin K–dependent clotting factor with the shortest half-life (6 hours: after 3-5 half-lives or 24-36 hours it will be eliminated from the body). The factor with the longest half-life, prothrombin or factor II, will take 5 days to clear from the body, hence why we need to bridge for at least 5 days AND until therapeutic INR is achieved.

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Warfarin Factors

This is a high-yield question that is often asked on exams and clinical rotations.  This mnemonic helps you remember which vitamin K-dependent factors warfarin affects. ⁠ Warfarin, brand name Coumadin, is an anticoagulant that acts by inhibiting the synthesis of vitamin K-dependent clotting factors, which include Factors II, VII, IX, and X, and the anticoagulant proteins C and S.⁠

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