You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Which of the following agents should not be used for oral anticoagulation in high risk patients with atrial fibrillation and explain in detail?
Oral anticoagulation in high-risk patients with AF includes vitamin K antagonists or the newer anticoagulants such as thrombin inhibi- tors (dabigatran) or factor Xa inhibitors (rivaroxaban, apixaban), but not antiplatelet agents (aspirin and clopidogrel), which have substantially less effect. Ref Harrison 20th edition pg 1456