Anticoagulation is the earliest and most widely used method in the treatment of lower extremity venous thrombosis. Anticoagulation itself cannot dissolve the formed thrombus, but it can inhibit the spread of the thrombus and cooperate with the body’s own fibrinolytic system to dissolve the thrombus, so as to achieve the purpose of treatment, and at the same time it can effectively reduce the occurrence of pulmonary embolism, which plays a pivotal role in the prevention and treatment of pulmonary embolism. Other surgical or non-surgical treatment methods should generally be accompanied by anticoagulation therapy as an adjuvant treatment. The duration of anticoagulation therapy can last for the whole course of the disease, usually 1 to 2 months, some patients can take up to 6 months to 1 year, and some even need lifelong anticoagulation. However, anticoagulation is contraindicated in the following cases: peptic ulcer, severe liver and kidney insufficiency, recent cerebral hemorrhage, post-abortion, congenital coagulation factor deficiency, etc. (1) Heparin is the most commonly used anticoagulant drug, and its anticoagulant effect is mainly through increasing the activity of antithrombin III (ATIII) to inhibit thrombosis. Heparin has a rapid onset of action, a short half-life, and a stable effect in vivo. Heparin is mainly administered by intravenous injection and deep subcutaneous fatty layer injection, and intramuscular injection is not suitable because of the risk of hematoma at the injection site. The subcutaneous deep fat layer injection method is simpler, but the concentration of heparin in the body is not easy to control precisely, and the injection site is usually chosen subcutaneously on the abdominal wall. The intravenous injection method uses micro-pump for continuous intravenous administration, which is a more ideal method of heparin administration because of its fast action, easy dose control and stable heparin concentration in the body, and easy adjustment. The specific method is to inject heparin 50mg or 6250U intravenously at one time, so that the concentration of heparin in the body can reach the peak quickly, and then heparin dilution solution (heparin 200mg or 25000U dissolved in 5% glucose saline 500ml) will be dripped continuously at 30ml/h intravenously. However, the dosage of heparin should be reduced to 20 ml/h in the following cases: those who have undergone surgery within 2 weeks; those who have had a stroke within 2 weeks; platelet count The dosage of heparin varies greatly among individuals, so the dosage of heparin should be adjusted at any time according to laboratory monitoring. The most commonly used indicator for monitoring heparin is the partial thromboplastin time. aPTT is controlled at 1.5 times the normal control or the upper limit of the normal value during the dosing period. aPTT is first tested after 6250 U of heparin is given intravenously, and then every 4-6 hours, and after stabilization, it can be tested every 12 hours. The common side effects of heparin include: A. Bleeding, the appearance of subcutaneous petechiae, petechiae during the use of the drug should be taken seriously, such as hematuria, gastrointestinal bleeding, then the drug should be reduced or stopped, bleeding in large amounts, the use of fisetin at a ratio of 1:1 intravenous injection, to counteract the anticoagulant effect of heparin. B. Thrombocytopenia, may be related to the autoimmune reaction caused by heparin in vivo, the incidence of 1% to 2%. The incidence of thrombocytopenia, which may be related to the autoimmune reaction caused by heparin, is 1%-2%, and is characterized by a decrease in platelet count and, in severe cases, widespread thrombosis in arteries and veins, resulting in death or mutilation of the patient. During the use of heparin, attention should be paid to the detection of platelet count. If thrombus spreads or new thrombus appears during the use of heparin, this complication should be considered, and the drug should be immediately discontinued and replaced by leechin or the selective antithrombin drug argatroban. c. Osteoporosis, when heparin is used for a long time, it may cause osteoporosis and even lead to vertebral or long bone fractures. (2) Low molecular weight heparin: As mentioned before, low molecular weight heparin has many superiorities over heparin. Since it mainly targets factor Xa, it is anticoagulated with a much lower risk of bleeding. With its good tissue absorption, long half-life, the method of administration becomes easier and the number of doses is reduced compared to heparin. There are several types of low molecular weight heparin available on the market, and the composition and usage of each product varies and cannot be generalized. What they all have in common is that they are mainly injected subcutaneously, once every 12 hours in case of deep vein thrombosis in the lower extremities. The use of low molecular weight heparin generally does not require laboratory monitoring, but like heparin, low molecular weight heparin can cause thrombocytopenia, and although its incidence is lower than that of heparin, testing platelet counts can help in the early detection of this complication. Since low-molecular-weight heparin is safer than heparin, it is increasingly used in clinical practice and has the tendency to gradually replace heparin. (3) Warfarin: Warfarin has been used clinically for a long time as an oral anticoagulant, and as an oral preparation, warfarin has become the drug of choice for outpatient anticoagulation therapy. Warfarin has a slow onset of action in the body, usually starting to take effect after 2-3 days of administration, so it is often used clinically together with heparin or low molecular weight heparin, and when warfarin reaches its therapeutic effect, heparin or low molecular weight heparin is discontinued. Usage: 7.5mg orally once on the first day, changed to 5mg orally once on the second day, 2.5mg/d orally on the third day, this dose is adjusted according to the prothrombin time (PT). PT is usually tested twice a week at the beginning to control the INR value to 2-3, and then changed to once a week, and gradually transitioned to once a month. The duration of warfarin in patients with lower extremity deep vein thrombosis is usually at least 2 months, and if there is a history of pulmonary embolism, the duration of warfarin can be extended to 1 year.