[Novel oral anticoagulants (NOAC)]

Novel oral anticoagulants (NOACs), a direct thrombin inhibitor (TDI), and direct factor Xa inhibitors (Xa-INHs) have mainly been used for prevention of stroke associated with atrial fibrillation in place of warfarin. DTI obstructs tenase by inhibiting thrombin generated in the initial phase and feedback to the amplification phase of cell-based coagulation reactions. Xa-INHs inhibit factor Xa activity in the prothrombinase complex of the propagation phase. Since the half-life of NOACs is in the approximate range of 8-14 hours, there are peak and trough periods in the blood concentrations of these agents. During the trough period, a small amount of thrombin is generated and plays a physiological role. The antithrombotic effect of NOACs is exerted during the peak period in combination with the effects of physiological coagulation inhibitors (PCIs) such as antithrombin in the trough period. Endothelial cells are the site for action of PCIs, such that it is important that they remain in a good state for effective anticoagulation by NOACs within the lesions. In a meta-analysis of NOACs vs. warfarin treatment, the former significantly reduced stroke or systemic embolic events by 19% as compared with warfarin, due mainly to a reduction in hemorrhagic stroke, while NOAC administration also significantly reduced intracranial hemorrhage by 52%.