Evidence for an antithrombotic effect of Dicumarol.

By the technique of serum-induced thrombosis, the effect of Dicumarol in depressing serum thrombotic accelerator (STA) activity was employed as a measure of the antithrombotic action of this drug in dogs. A significant antithrombotic effect, unassociated with hemorrhage, was achieved at levels of prothrombic activity below 15% of the control values. The antithrombotic effect of Dicumarol, as distinct from the anticoagulant effect, was demonstrable only after a latent period of approximately 1 week or more, unless massive doses of the anticoagulant were administered. No clear-cut correlation was evident between depression of STA activity and depression of any coagulation factor singly or in combination known to be affected by Dicumarol. The data reported in this communication represent the first demonstration that Dicumarol may inhibit in vivo thrombus formation (as distinct from in vitro clot formation) mediated exclusively through activation of the intrinsic clotting system.