Atrial fibrillation (AF) confers a 4.5% risk of stroke per year. The risk of stroke increases with various risk factors and until recently, warfarin has been the gold standard of thromboembolism prophylaxis in AF for many years. The dosage of warfarin requires regular adjustment dependent on the INR, to keep within a narrow therapeutic range of 2.0- 3.0.
The INR can be altered by concomitant drugs, foods and alcohol and requires inconvenient blood monitoring. Underanticoagulation places patients at risk of stroke, whilst over-anticoagulation confers significant bleeding risk. Consequently approximately half who would benefit from oral anticoagulation do not have it prescribed.
Novel oral anticoagulants with predictable pharmacokinetics and improved efficacy and safety profiles are currently being developed for stroke prevention in AF. Three novel oral anticoagulants have just completed Phase III trials for stroke prevention, all with impressive results; the direct thrombin inhibitor, dabigatran and the oral factor Xa inhibitors, rivaroxaban and apixaban.