Over the past 6 decades, warfarin has proven efficacious in reducing stroke risk in patients with atrial fibrillation and reducing the risk of recurrent venous thromboembolism in patients with acute deep vein thrombosis or pulmonary embolism. However, there have been multiple challenges with using warfarin including delayed onset of action, need for bridging and monitoring as well as many drug-drug and drug-food interactions. Hence, long years of research have led to the development of direct oral anticoagulants. Of the 4 direct oral anticoagulants currently approved by the Food and Drug Administration, 1 is a direct thrombin inhibitor (dabigatran) and the other 3 are direct factor Xa inhibitors (apixaban, rivaroxaban and edoxaban). Direct oral anticoagulants have been found to be at least as effective as warfarin with fewer bleeding complications. This paper provides an overview of the evolution of anticoagulation therapies and an extensive literature review of the new direct oral anticoagulants.
KEY WORDSanticoagulation, direct oral anticoagulant, bleeding n INTRODUCTIONIn the 1920s, cattle in Canada and the northern United States suffered from severe internal bleeding that was associated with diet. It was discovered that spoiled sweet clover hay (Melilotus alba and Melilotus officinalis) contained a hemorrhagic factor, a coumarin compound that was isolated and named dicoumarol, that reduced the activity of prothrombin.1,2 A related derivative, warfarin, was initially used as a rodenticide and eventually moved to clinical application. Warfarin acts as an inhibitor of vitamin K epoxidase reductase, which catalyzes the reduction of oxidized vitamin K.3 The latter is essential for the carboxylation of coagulation proteins for factors II, VII, IX, and X. 4,5 Based on multiple clinical trials, warfarin was proven to reduce stroke risk in patients with atrial fibrillation (AF) and to reduce recurrent venous thromboembolism (VTE) after the initial event.6 However, warfarin has multiple pitfalls including delayed therapeutic onset, interindividual variability in anticoagulant effect, significant drug-drug and drug-food interactions, dietary restrictions, and an increased need for monitoring. 4,7 Research to develop more convenient new anticoagulation therapies with better efficacy and fewer side effects has been ongoing for decades. Based on their mechanism of action, the direct oral anticoagulants (DOACs) can be divided into 2 groups: direct thrombin (factor IIa) and direct FXa inhibitors. 4 The effects of DOAC are seen within a few hours of ingestion, generally require no monitoring, and have fewer drug-drug interactions when compared with warfarin. Furthermore, they have been proven to be at least as effective as warfarin with fewer bleeding complications. 8,9 The Food and Drug Administration (FDA) has approved idarucizumab as a specific antidote to dabigatran and is currently considering andexanet alfa as a reversal agent for the available anti-Xa agents. This paper will review the novel anticoagulant ther...