Outpatient Management of Anticoagulation Therapy
ANNE L. DU BREUIL, M.D., and ELENA M. UMLAND, PHARM.D. Thomas Jefferson University, Philadelphia, Pennsylvania
The Seventh American College of Chest Physicians (ACCP) Conference on Antithrombotic and Thrombolytic Therapy provides guidelines for outpatient management of anticoagulation therapy. The ACCP guidelines recommend short-term warfarintherapy, with the goal of maintaining an International Normalized Ratio (INR) of 2.5 ± 0.5, after major orthopedic surgery. Therapy for venous thromboembolism includes an INR of 2.5 ± 0.5, with the length of therapy determined by associated conditions. For patients with atrial fibrillation, the INR is maintained at 2.5 ± 0.5 indefinitely; for most patients with mechanical valves, therecommended INR is 3.0 ± 0.5 indefinitely. Use of outpatient low-molecular-weight heparin (LMWH) is as safe and effective as inpatient unfractionated heparin for treatment of venous thromboembolism. The ACCP recommends starting warfarin with unfractionated heparin or LMWH for at least five days and continuing until a therapeutic INR is achieved. Because patients with venous thromboembolism and cancer whohave been treated with LMWH have a survival advantage that extends beyond their venous thromboembolism treatment, the ACCP recommends beginning their therapy with three to six months of LMWH. When invasive procedures require the interruption of oral anticoagulation therapy, recommendations for bridge therapy are determined by balancing the risk of bleeding against the risk of thromboembolism.Patients at higher risk of thromboembolization should stop warfarin therapy four to five days before surgery and start LMWH or unfractionated heparin two to three days before surgery. (Am Fam Physician 2007;75:1031-42. Copyright © 2007 American Academy of Family Physicians.)
arfarin (Coumadin), unfractionated heparin, and lowmolecular-weight heparins (LMWHs) are used for the treatment ofvenous thromboembolism (VTE), the prevention of systemic embolism associated with atrial fibrillation or the use of prosthetic heart valves, and the prevention of stroke and recurrent myocardial infarction in select patients.1 The LMWHs have changed the course of outpatient anticoagulation therapy because patients no longer need to remain hospitalized for the initiation of oral therapy in acuteVTE or for bridge therapy when undergoing invasive procedures that require temporary discontinuation of warfarin. This article focuses on indications for warfarin and LMWH therapy, how to initiate therapy, therapeutic goals, troubleshooting common issues, and duration of therapy. Many of the recommendations are derived from a recent evidence-based practice guideline from
the SeventhAmerican College of Chest Physicians (ACCP) Conference on Antithrombotic and Thrombolytic Therapy.1-9 Warfarin
mechanism of action
Warfarin interferes with the cyclic interconversion of vitamin K and vitamin K epoxide and subsequent modulation of the gamma carboxylation of the terminal regions of vitamin K proteins. This results in the reduction of clotting factors II, VII, IX, and X.1Carboxylation of the regulatory anticoagulant proteins C and S also is inhibited, potentially contributing to a procoagulant effect early in therapy. Reduction of the clotting factors II, VII, and X is measured using the prothrombin time.1 Because of interlaboratory variability in the thromboplastins used to measure the prothrombin time, use of the International Normalized Ratio (INR) has become thestandard of practice, making values obtained from various laboratories comparable.
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