The higher rates of bleeding episodes encountered in patients treated with rivaroxaban may be ascribed to the fact that rivaroxaban slightly prolongs prothrombin time and partial thromboplastin time [20,21], while apixaban is a highly selective factor Xa (FXa) inhibitor of both free and bound FXa, as well as prothrombinase, independent of antithrombin III for the prevention and treatment of thromboembolic diseases [22]. This evidence concerns the gene F2 and Thromboembolism.