Abstract: The present disclosure refers to a method and compositions for reducing the occurrence of thrombosis or thromboembolism in a patient identified as being at risk thereof, the method comprising administering to the patient a therapeutically effective amount of one or more anticoagulant selected from the group consisting of unfractionated heparin, a low molecular weight heparin, a heparinoid, fondaparinux, idraparinux, and combinations thereof, and antithrombin III (ATIII).