Why is Heparin started before starting Warfarin therapy in thrombotic disorders?

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Why is Warfarin not started directly?

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When warfarin is newly started, it may promote clot formation temporarily. This is because the level of protein C and protein S are also dependent on vitamin K activity. Warfarin causes decline in protein C levels in first 36 hours. In addition, reduced levels of protein S lead to a reduction in activity of protein C (for which it is the co-factor) and therefore reduced degradation of factor Va and factor VIIIa. Although loading doses of warfarin over 5 mg also produce a precipitous decline in factor VII, resulting in an initial prolongation of the INR, full antithrombotic effect does not take place until significant reduction in factor II occurs days later. The haemostasis system becomes temporarily biased towards thrombus formation, leading to a prothrombotic state. Thus, when warfarin is loaded rapidly at greater than 5 mg per day, it is beneficial to co-administer heparin, an anticoagulant that acts upon antithrombin and helps reduce the risk of thrombosis, with warfarin therapy for four to five days, in order to have the benefit of anticoagulation from heparin until the full effect of warfarin has been achieved.

answered Dec 11, 2014 by admin Doctor of Medicine (10,059 points)

Warfarin inhibits clotting factors 2,7,9,10 plus it inhibits protein c and s which are natural anticoagulants... So to initiate its action it takes time...while heparin acts on antithrombin 3...so given before warfarin...

answered Dec 14, 2014 by anonymous