tailieunhanh - JUST THE FACTS IN EMERGENCY MEDICINE - PART 8

Định lượng được hướng dẫn bởi tỷ lệ chuẩn hóa quốc tế (INR), có nguồn gốc từ thời gian prothrombin (PT), INR mong muốn thường là giữa 2,0 và 2,5. Khởi đầu của kháng đông xảy ra sau khi 3 đến 4 ngày. • Warfarin cũng ảnh hưởng đến protein | 412 SECTION 16 HEMATOLOGIC AND ONCOLOGIC EMERGENCIES ANTITHROMBOTIC AGENTS ORAL ANTICOAGULANT Warfarin inhibits vitamin K-dependent clotting factors II VII IX X . Dosing is guided by the international normalized ratio INR derived from the prothrombin time PT the desired INR is usually between and . Onset of anticoagulation occurs after 3 to 4 days. Warfarin also affects proteins C and S and for 24 to 36 h there may be a hypercoagulable effect this is minimized by a starting dose of 5 mg day. In situations where immediate anticoagulation is critical a heparin product should be used until an adequate INR is achieved. Warfarin is contraindicated in pregnancy. PARENTERAL ANTICOAGULANTS Unfractionated heparin forms a complex with antithrombin III ATIII which inhibits factors IXa and Xa. Body weight-based IV dosing is recommended typically 70 to 80 U kg IV bolus followed by IV infusion at 15 to 18 U kg h. Therapy is monitored by the activated partial thromboplastin time aPTT the therapeutic range is to times the normal value. Low-molecular-weight LMW heparin fractions enoxaparin dalteparin and ardeparin are derived from unfractionated heparin. These agents are effective when administered SC once to twice daily. LMW heparin is used for both prophylaxis and treatment. Enoxaparin is FDA-approved for the prophylaxis of deep venous thrombosis DVT and for treatment of DVT with or without pulmonary embolism PE non-Q-wave myocardial infarction MI and unstable angina. For DVT PE and unstable angina enoxaparin 1 mg kg SC bid or dalteparin 100 IU kg SC bid may be used. The heparins and danaparoid may be used in pregnancy. LMW heparins and danaparoid produce minimal elevation in prothrombin time PT or aPTT laboratory monitoring is not routinely necessary except in renal failure where anti-Xa activity can be measured. PLATELET ACTIVATION BLOCKER Aspirin blocks the enzyme cyclooxygenase which results in inhibition of platelet activation. The in hibitory effect is .