Heparin is needed in the initial treatment of venous thromboembolism. Warfarin can be commenced on the day of diagnosis and heparin must be continued for 5 days or until the international normalized ratio (INR) is greater than 2.0 for 2 consecutive days, whichever is the longer.
Low molecular weight heparins (LMWH) have largely replaced unfractionated heparin. Their much more predictable anticoagulant response combined with high bioavailability after subcutaneous injection means that the dose can be calculated by body weight and given subcutaneously without any monitoring or dose adjustment. Their widespread use has enabled most patients with deep vein thrombosis to be managed as outpatients, and this is also increasingly the case for uncomplicated pulmonary embolism.
Particular issues—(1) in patients with cancer, giving LMWH for the first 6 months of long-term anticoagulant therapy has been shown to be superior to switching to a vitamin K antagonist; (2) high-dose loading regimens of warfarin are unnecessary and may increase the risk of overanticoagulation and bleeding; (3) warfarin for venous thromboembolism and atrial fibrillation should be given with a target INR of 2.5 (range 2.0–3.0); for patients with prosthetic heart valves the target INR is usually greater; (4) indefinite anticoagulation is required for patients with atrial fibrillation or a mechanical heart valve; for venous thromboembolism a careful clinical decision is required regarding duration of treatment; (5) for patients with atrial fibrillation and other risk factors for stroke, the superior efficacy of warfarin as compared to aspirin makes it the treatment of choice; (6) if warfarin needs to be stopped for surgery, full-dose heparin does not have to be given perioperatively unless the risk of thromboembolism is high, and warfarin can be continued in patients having dental extractions; (7) new oral anticoagulants specifically targeting thrombin or factor Xa have been developed and are likely to replace warfarin for many indications over the next decade.
Chapter. 4427 words. Illustrated.
Subjects: Cardiovascular Medicine
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