What Are the Rules in the Monitoring of Oral Anticoagulants?
Warfarin is rapidly absorbed after oral administration. However, anticoagulant effects are delayed until the nor-mal clotting factors are replaced by the decarboxylated vitamin PC-dependent clotting factors. The delay may range from 2 to 7 days or even more according to the dosage. During the initial 24-48 h of oral anticoagulant therapy, an early prothrombotic effect may result from reduction of protein C activity which is linked to its short half-life. Factors VII (the most rapidly inhibited factor, e.g. 2 h after an oral loading dose), IX and X respond slowly to the effects of warfarin, whereas hypoprothrombinemia is usually induced in 36-72 h. Because the half-life of warfarin is about 2.5 days, the effect on coagulation may last for 4-5 days. Different laboratory tests are available for measuring the biologic activity of oral anticoagulants. The most commonly used test is the one-stage prothrombin time (PT), which is sensitive to reductions in factors II, VII and X. The interpreta
