The onset of action of warfarin: Since the onset of action of warfarin depends on the significant decrease of the synthesized thrombinogen (factor II) in the body, and the half-life of factor II is 72 hours, so it takes at least 3 days for oral warfarin to really take effect, and the maximum effect time of anticoagulation is 72-96 hours, and the maximum effect time of antithrombosis is 6 days, therefore, heparin or low-molecular heparin should be preferred for those who need anticoagulation urgently. Generally, after the anticoagulant effect of full dose of heparin has appeared, then warfarin is used for long-term anticoagulation therapy. At the same time, its efficacy can be stabilized only after 5-7 days of administration, and the adequacy of the maintenance dose can be judged only after 5-7 days of observation. Monitoring the initial dose of warfarin: Increasing the initial dose of warfarin does not accelerate the clearance of synthesized factor II, but the high dose may lead to hypercoagulability and even thrombosis in the initial phase due to the reduced synthesis and rapid clearance of protein C and protein S. Therefore, the initial dose of warfarin is 5mg-10mg, currently recommended to be 3mg in China. if rapid anticoagulation is needed, heparin can be given at the same time, and the two overlap for at least 4 days, and heparin is discontinued after 2 days of reaching the treatment standard. The starting dose should be reduced for warfarin-sensitive patients, the elderly, and those with a high risk of bleeding. The absorption, pharmacokinetics and pharmacodynamics of warfarin are influenced by food, genetics, and disease status, so the safety of treatment should be ensured by monitoring prothrombin time (PT) and international normalized ratio (INR) after administration. Be aware of bleeding due to warfarin: Warfarin overdose is prone to bleeding and is closely related to INR, with an increased risk of bleeding at INR>4 and a dramatic increase at INR>5. In case of anticoagulation overload, INR over range and high risk bleeding tendency, warfarin needs to be reduced or discontinued, and the INR should be monitored to reduce to the target range before starting the application from a small dose. If the patient has a high-risk bleeding tendency and the INR needs to be brought down to normal within 24 hours, vitamin K1 may be given orally at 1 mg to 2.5 mg. Emergency correction should be done by slow sedation of vitamin K 15 mg to 10 mg (>30 min, 4 hours required to restore coagulation after sedation). When there is severe bleeding or INR>20, vitamin K110mg, fresh plasma and prothrombin complex can be applied slowly by sedation. High doses of vitamin K1 can cause warfarin resistance and warfarin should be reintroduced with concurrent administration of heparin until the patient regains sensitivity to warfarin. Pay attention to monitoring the international normalized ratio: Warfarin should be monitored daily at the beginning of treatment, and after stabilization for at least 2 days the drug may be given 2 to 3 times a week until the fourth week. Studies have shown that warfarin has the highest incidence of bleeding within 6 to 12 weeks of treatment initiation, and it is best to check weekly. Even in those with a stable INR, the dose should not be taken between monitoring periods for more than 4 to 6 weeks.