What should be the target INR in a patient on warfarin therapy?
For most indications, warfarin is administered in doses that produce a target INR of 2.0- 3.0. An exception is patients with mechanical hea valves, where a target INR of 2.5-3.5 is recommended. Studies in atrial fibrillation demonstrate an increased risk of cardio embolic stroke when the INR falls to 4. Warfarin interferes with the synthesis of the vitamin K-dependent clotting proteins, which include prothrombin (factor II) and factors VII, IX, and X. Like all anticoagulants, the major side effect of warfarin is bleeding. A rare complication is skin necrosis. Warfarin crosses the placenta and can cause fetal abnormalities. Consequently, warfarin should not be used during pregnancy. Dabigatran etexilate, an oral thrombin inhibitor, and rivaroxaban, an oral factor Xa inhibitor are new oral anticoagulants.
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