Heparin/low molecular weight heparin and tissue factor pathway inhibitor.

Tissue factor pathway inhibitor (TFPI) is the factor Xa (FXa)-dependent coagulation inhibitor. TFPI is released to the blood after injection of heparin or low molecular weight heparin (LMWH). The post-heparin anticoagulant effect is caused by this release of TFPI. Free TFPI has higher affinity for heparin than TFPI which is associated with lipoproteins. Heparin increases the rate of inactivation of FXa and of tissue factor-F VIIa by TFPI. Immunoblocking of TFPI reduces the anticoagulant effect of heparin in blood activated by tissue factor considerably. Both antithrombin and TFPI participate in the anticoagulant effect induced by heparinization of blood or plasma.