Until recently, the only OAC used was warfarin. Warfarin reduces stroke by ~60% and death by ~25% compared with no treatment. Despite its clinical efficacy, warfarin has multiple, well-known limitations, including numerous interactions with other drugs and the need for regular blood monitoring and dose adjustments. Thus, warfarin therapy may be underused or inappropriate for patients with atrial fibrillation.
In the past 10 years, novel drugs have been developed that may ultimately replace warfarin for patients with AF. The direct thrombin and factor Xa inhibitors overcome the need for routine blood monitoring, and the trial results have been encouraging overall. Three new drugs (apixaban, dabigatran, and rivaroxaban), all significantly reduce the risk of hemorrhagic stroke (bleeding into the brain) as compared with warfarin. Of the three drugs, only dabigatran at a dose of 150 mg holds the distinction of also having significantly reduced the risk of ischemic stroke (strokes caused by a blood clot) as compared with warfarin. Furthermore, the risk of particularly serious bleeding was reduced with each of the three drugs, as compared with warfarin.
Switching to a newer agent may not be necessary for the individual patient in whom the INR has been well controlled with warfarin for years. In addition, although the newer anticoagulants have a more rapid onset and termination of anticoagulant action than does warfarin, agents to reverse the effect of the drugs are still under development and are not routinely available. In addition, generic warfarin is expected to be markedly less expensive than the newer agents even after the costs associated with regular INR monitoring are considered. Thus, although the new drugs are attractive alternatives, it is likely that warfarin will continue to be used worldwide in many patients with AF.