This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bleeding and Thrombotic Disorders, Subject name: Medicine
[{'content': 'INR in warfarin therapy is? \nSelect and explain. \nA. 1.5, B. 2.5, C. 3.5, D. 4.5', 'role': 'user'}, {'content': 'Answer: B \nExplanation: ANSWER: (B) 2.5REF: Harrison 18th ed chapter 118For most indications, warfarin is administered in doses that produce a target INR of 2.0- 3.0. An exception is patients with mechanical heart valves, where a target INR of 2.5-3.5 is recommended. Studies in atrial fibrillation demonstrate an increased risk of cardioembolic stroke when the INR falls to <1.7 and an increase in bleeding with INR values >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.', 'role': 'assistant'}]