1.Why do oral antithrombotic drugs need to be monitored? Antithrombotic treatment is often needed after thrombotic diseases or vascular surgery. Warfarin is the most commonly used oral anticoagulant drug, which is an antagonist of vitamin K. After oral administration, it achieves the purpose of antithrombotic by interfering with the carboxylation of vitamin K-dependent coagulation factors II, VII, IX and X, so that these coagulation factors cannot be activated and can only stay in the precursor phase. But in the human body to stop thrombus formation is another important physiological function to prevent bleeding disorders, and excessive inhibition can lead to bleeding disorders. Therefore, the use of anticoagulant drugs must be controlled at a reasonable intensity, to the extent that it can prevent intravascular thrombosis without spontaneous bleeding, which requires accurate monitoring. 2.Why should INR be monitored? Since the coagulation factors inhibited by warfarin mainly function in the exogenous coagulation system, the activity of the exogenous coagulation system should be monitored, and in clinical practice the effect of anticoagulation is mainly reflected by monitoring the prothrombin time (PT). PT assay is performed in vitro by adding reagents similar to tissue factor to plasma to initiate exogenous coagulation system and observing the time of plasma clotting. Because the procoagulant activity of the reagents used in the PT assay varies, the same plasma tested with different reagents yields different PT values, which makes comparison impossible. To solve this problem, a clinically standardized PT is used, the International Normalized Ratio (INR), which is derived by a complex calculation using the formula INR=PTRISI, where ISI is the International Sensitivity Index, representing the procoagulant activity of the prothrombin reagent, and PTR is the ratio of the subject’s PT to the normal plasma PT. The standardized PT (INR) is used to reflect the effect of anticoagulation, so that the same plasma using different sensitivity reagents gives the same result, which is convenient for clinical comparison. 3.How to adjust the dose of warfarin according to INR? The initial dose of warfarin for Chinese is recommended to be 2.5-3mg once daily, with a target INR of 2.0-3.0 depending on the condition, and the target INR can be adjusted down to 1.6-2.5 for elderly people older than 75 years old and for patients at high risk of bleeding. If the INR is below 1.5, increase the dose by 1/4 tablet per day, if the INR does not change much from the basal level, increase the dose by 1/2 tablet per day, if the INR does not reach the standard but is above 1.5, do not increase the dose temporarily and wait for the result of INR measurement on day 7. Therefore, the INR should be monitored three times during the first week of oral warfarin, and then once a week until the fourth week. After the INR has reached its target value and stabilized (two consecutive times within the target range of treatment), the INR should be checked every 4 weeks. If a high or low INR is encountered, the timing of the next INR observation should be determined based on the INR value and the dose adjustment of warfarin. Although warfarin is safe when used properly, it is best not to use it until the physician has mastered its use, especially in places where monitoring conditions are not available. There are also some hospitals that use warfarin in a fixed small dose without monitoring INR, this method should not be advocated, some experiments have shown that this method is not effective and not absolutely safe. 4.What factors affect INR? Warfarin is metabolized by the liver in the body, so patients with reduced liver function need to reduce the dosage of warfarin; the metabolites of warfarin are excreted by the kidneys, but the metabolites have no anticoagulant activity, so patients with renal insufficiency do not need to reduce the dosage of warfarin. There are also many factors, such as diet, other diseases and other drugs can affect the anticoagulant effect of warfarin, that is, affect the INR. for example, green leafy vegetables contain more vitamin K, after eating a large amount can reduce the anticoagulant effect of warfarin, while broad-spectrum antibiotics inhibit intestinal flora, so that the body vitamin K content decreases, will increase the efficacy of warfarin; anti-platelet drugs can have synergistic effects with warfarin, bleeding side effects Increase; chloral hydrate, hydroxybacterium, methanesulfonate urine, etc. can replace plasma protein, so that the concentration of plasma warfarin increases, the anticoagulant effect is enhanced; salicylate, metronidazole, cimicifugine, etc. can inhibit liver drug enzymes to reduce the metabolism of warfarin, so that its anticoagulant effect is enhanced. Therefore, in order to maintain the stable anticoagulation strength of warfarin, patients must pay attention to the application of related drugs, and should also maintain the relative balance of diet, so as to ensure the safety and effectiveness of warfarin anticoagulation therapy.