1, why patients with atrial fibrillation need anticoagulation therapy The main danger of atrial fibrillation is thrombosis and embolism. In order to reduce the incidence of atrial fibrillation embolism need to take anticoagulant drugs, which is a very important part of atrial fibrillation treatment. Clinically, patients are scored according to their risk of embolism, with warfarin for high-risk patients and oral aspirin or no medication for low-risk patients. These risk factors include: previous history of embolism, transient ischemic attack, age ≥75 years; heart failure or moderate to severe cardiac systolic insufficiency (left ventricular ejection fraction ≤40％), hypertension, diabetes mellitus, female, age 65-74 years, and vascular disease. The more risk factors, the greater the risk. In addition, the patient’s risk of bleeding should also be evaluated, and if the patient’s risk of bleeding is too great he should not take warfarin. 2, which patients taking warfarin bleeding risk patients before taking warfarin to understand their risk of bleeding. Factors associated with a high risk of bleeding on antithrombotic drugs include: hypertension, abnormal liver/kidney function, stroke, history of bleeding or bleeding tendency, unstable INR (International Normalized Ratio, an indicator of coagulation), age >65 years, use of antiplatelet or non-steroidal anti-inflammatory drugs, and alcoholism. If a patient has ≥3 of these risk factors, the risk of bleeding is higher, and such patients taking antithrombotic drugs (either warfarin or aspirin) need to be reviewed carefully and regularly. 3, taking warfarin anticoagulation need to be noted because many foods and drugs can have an effect on the anticoagulant effect of warfarin, so patients with atrial fibrillation taking warfarin must regularly review INR on an outpatient basis. usually recommended to take the medication at night, the first outpatient review is after 3 days of taking the medication, after which the dose is adjusted according to the results of the review and the next review time is decided. The INR should be reviewed once a week when you start taking warfarin and once a month after the INR has stabilized. If you are taking drugs that affect warfarin or have changed your diet, you should review your INR and adjust your warfarin dosage. In addition, warfarin is generally not taken at the same time as aspirin, which can increase the risk of bleeding. 4. Optimal target value of INR Since low levels of INR have a high risk of stroke and high levels of INR increase the risk of bleeding, warfarin anticoagulation means that the INR needs to be adjusted to achieve a balance between the two. Clinical trials in Europe and the United States have demonstrated that anticoagulation at an intensity of INR 2.0 to 3.0 is effective in preventing stroke events, reducing the annual incidence of stroke from 4.5% to 1.5% and reducing the relative risk by 68%, without significantly increasing the risk of cerebral hemorrhage. If the INR was below 2.0, there were fewer bleeding complications but significantly less thrombosis prevention; with an INR above 4.0, there was less thrombosis but significantly more bleeding complications. However, there is evidence that intracranial hemorrhage associated with warfarin is 4.06 times higher in Asians than in Caucasians. A domestic study has looked at the optimal range of INR in the Chinese population and the results suggest that maintaining an INR of 2.0 to 2.5 may be more appropriate for the Chinese population. However, more evidence is needed on the optimal anticoagulation strength of warfarin in Chinese. 5, how to make warfarin dose adjustment When the drug is first started, warfarin dose adjustment should be based not only on the measured value of INR, but also on the trend of INR changes. Generally, on the 5th day after the application of warfarin, if the INR has a rising trend, but has not yet reached the lower limit of the therapeutic target, it should be noted that the dose needs to be reduced if necessary. It should be noted that the INR does not change until several days after warfarin dose adjustment, so dose adjustment should not be too frequent. If the INR of a patient taking warfarin for a long period of time is measured several times the result lies steadily outside the target range. Patients with high INR fluctuations are most likely to have thromboembolism or bleeding complications, and these patients should be reminded to pay attention to the diet These patients should be reminded to maintain a stable intake of vitamin K, take their medication as prescribed, and monitor their INR regularly. If a patient taking warfarin has had a recent fluctuation in INR, below the target range of 0.2 or above the target range of 0.4, the reasons for INR fluctuations should be sought, including: laboratory measurement errors, failure to take medication as prescribed, temporary application of medications that interact with warfarin, a large fluctuation in dietary intake of vitamin K or a change in health status. If the cause of INR fluctuations is not found, the warfarin dose should be changed and the INR should be readjusted, and the measurement should be repeated within 2 weeks. Warfarin dose adjustment is based on the magnitude of the INR deviation from the target range and the patient’s previous response to warfarin dose adjustment. In most cases warfarin is increased or decreased by 5％ to 20％ too large a change, such as more than 1/3 of the original dose, and the INR may be overkill. What’s more, patients need to be reminded that the dose must be adjusted under the supervision of a doctor when they start taking warfarin, because warfarin can vary in anticoagulation strength between different people or even the same person in different states, and if patients adjust the dose themselves, it can increase the risk of complications. 6, factors that may affect the efficacy of warfarin Common drugs that can increase the anticoagulant effect of warfarin include: amiodarone, propafenone, morethizide, omeprazole, cimetidine, erythromycin, ofloxacin, ciprofloxacin, cephalosporin, metronidazole, paracetamol, aspirin, etc. Common drugs and foods that can reduce the anticoagulant effect of warfarin include barbiturates, rifampin, cyclosporine A, and foods rich in vitamin K (see Table 3). Atenolol and metoprolol have almost no effect on warfarin. You should be aware that the above mentioned drugs or foods are not inadmissible, but should be eaten on a relatively regular daily basis in the diet, and new drugs should be reviewed in a timely manner. The adjusted warfarin dose in the context of the same food and drug is reliable.