Clinical trials in the 1990s demonstrated that antithrombotic therapy, especially warfarin, can prevent strokes in trial participants who have chronic atrial fibrillation (AF). Because most trial participants were younger than age 80, the safety and benefits of prescribing antithrombotic therapy to very elderly patients have been controversial. Clarifying the safety and benefits for octogenarians is important because the risk of stroke, the prevalence of chronic AF, and the occurrence of adverse events from anticoagulation increase with age.
In a recent review article, Brian F. Gage, M.D., M.Sc., of the Washington University School of Medicine, and colleagues at the University of Washington and the University of California at Davis use the case of an otherwise healthy 80-year-old man who has AF and hypertension—conditions that increase the risk of stroke—to clarify the risks and benefits of prescribing warfarin in the very elderly. They estimate that this patient has a 4 percent stroke risk without warfarin therapy and a 3 to 4 percent risk for hemorrhage with warfarin, and that warfarin is likely to prolong survival by about 0.1 quality-adjusted life-year more than aspirin would. However, this latter estimate is sensitive to the risk of hemorrhage and the patient's preferences.
Compared with aspirin, warfarin would reduce his stroke rate by 2 percent per year and increase his risk of major hemorrhage by 2 to 3 percent per year. After discussing these risks, the patient understands that stroke is usually much more debilitating then hemorrhage, and he chooses to take warfarin and undergo regular blood monitoring (via international normalized ratio [INR] testing).
Based on several prior studies, the researchers conclude that the optimal INR for patients who have nonvalvular AF is at least 2.0; the optimal INR remains controversial, especially in an 80-year-old patient, but they choose a target INR of 2.5. Because advanced age is associated with lower steady-state warfarin dose requirements, many experts initiate warfarin therapy with an initial dose of 2 to 4 mg rather than a higher dose. A reasonable plan is to check the INR of outpatients two to four times during the first week of warfarin therapy and twice during the second week. The time between INR tests should be increased gradually as a steady-state response (optimal thinness of blood) is achieved.
See "Warfarin therapy for an octogenarian who has atrial fibrillation," by Dr. Gage, Stephan D. Fihn, M.D., M.P.H., and Richard H. White, M.D., in the March 20, 2001 Annals of Internal Medicine 134, pp. 465-474.