Emerging Anticoagulant Therapies for Atrial Fibrillation: New Options, New Challenges

Atrial fibrillation (AF), the most common cardiac arrhythmia, is associated with an increased risk of stroke and systemic embolism. Oral anticoagulation with vitamin K antagonists (VKAs), such as warfarin, has historically been the mainstay of long-term thromboprophylaxis in AF patients. However, although highly effective, VKAs have a number of limitations that make their use difficult and cumbersome in clinical practice. They have a slow onset and offset of action, narrow therapeutic window, marked dose-response variability, and multiple food and drug interactions, and require frequent coagulation monitoring and dose adjustments. To overcome VKA drawbacks, several new oral anticoagulants have been recently developed for use in AF, and three of them, the direct thrombin inhibitor dabigatran etexilate and the direct factor Xa inhibitors rivaroxaban and apixaban, have completed phase III trials. New agents have proven to be noninferior or superior to warfarin for AF-related stroke prevention, with similar or better safety profiles. These new drugs, with their predictable anticoagulant effect that allows for fixed dosing with no need for coagulation monitoring, have the potential to greatly simplify anticoagulation therapy for AF. Dabigatran etexilate and rivaroxaban are already approved in the United States and Europe for stroke prevention in nonvalvular AF, and dabigatran etexilate has entered current AF guidelines as an alternative to warfarin. However, some issues with new compounds are still unresolved, such as the lack of antidotes and standardized tests to measure drug activity. Active postmarketing monitoring surveillance of effectiveness and safety is required in the implementation of new anticoagulant therapies.