To the Editor: Patients may require long term anticoagulation for reasons that commonly include deep vein thrombosis, pulmonary embolism or atrial fibrillation.1 In these circumstances, heparin is commonly used for bridging and is discontinued after the effects of warfarin result in a therapeutic international normalisation ratio. It takes approximately 5 days for this to occur because warfarin inhibits the production of vitamin K‐dependent clotting factors II, VII, IX and X.2 The time to therapeutic anticoagulation is a reflection of the half‐lives of the circulating clotting factors and the time for them to diminish from the plasma. This has been our mindset for decades from the perspective of warfarin use.
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- 1. Holbrook A, Schulman S, Witt DM, et al. Evidence‐based management of anticoagulant therapy: antithrombotic therapy and prevention of thrombosis, 9th ed: American College of Chest Physicians evidence‐based clinical practice guidelines. Chest 2012; 141: e152S–e184S.
- 2. Kovacs MJ, Rodger M, Anderson DR, et al. Comparison of 10 mg and 5 mg warfarin initiation nomograms together with low‐molecular‐weight heparin for outpatient treatment of acute venous thromboembolism. A randomized, double‐blind, controlled trial. Ann Intern Med 2003; 138: 714–719.
- 3. Dubois V, Dincq AS, Douxfils J, et al. Perioperative management of patients on direct oral anticoagulants. Thromb J 2017; 15: 14.
- 4. Mueck W, Stampfuss J, Kubitza D, et al. Clinical pharmacokinetic and pharmacodynamic profile of rivaroxaban. Clin Pharmacokinet 2014; 53: 1–16.
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