Aspirin is only recommended for patients with lone atrial fibrillation who are younger than 65 and with no other risk factors for thromboembolism and for those who are intolerant to warfarin administration. Aspirin’s risk reduction of stroke is less than 20%. Patients with lone atrial fibrillation who are younger than 65 have a low stroke rate of approximately 1% versus patients over age 75 with one or more additional risk factors for thromboem-bolism who have a stroke rate of greater than 8%. Lone atrial fibrillation is indicated by the absence of hyperten¬sion and valvular and other heart disease.
B. New Anticoagulant: Ximelagatran
This direct thrombin inhibitor has been shown to be as effective as warfarin in preventing stroke and does not require monitoring with blood tests. The drug represents a major breakthrough for management of atrial fibrillation and control of thromboembolism. The stroke prevention with the oral direct thrombin inhibitor ximelagatran, compared with warfarin in patients with nonvalvular atrial fibrillation (SPORTIF) III and V randomized trials, studied patients at moderate risk. Patients with mitral stenosis, significant valve disease, or previous valvular heart surgery were excluded. Thus the new agent if approved should be used only in patients similar to those in the SPORTIF trials. Caution: in both trials the new drug caused substantial but usually transient increases in liver enzyme concentrations in 6% of patients. Enzyme eleva¬tions reached greater than five times the upper limits of normal in 3.4% of ximelagatran-treated patients (see the chapter Blood Clots). Hepatotoxicity limits the use of the drug and similar agents should be sought.

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