In the same year, Kamath et al3 randomized 70 patients with nonvalvular atrial fibrillation to either dose-adjusted warfarin (international normalized ratio, 2 to 3) or combination therapy with aspirin (75 mg/d) and clopidogrel (75 mg/d). Pretreatment levels of fibrin d-dimer, β-thromboglobulin, and soluble P-selectin were raised in patients with atrial fibrillation, whereas plasma prothrombin fragment 1 + 2 levels and platelet aggregation were not different from control subjects. Dose-adjusted warfarin reduced plasma levels of fibrin d-dimer, prothrombin fragment 1 + 2 and β-thromboglobulin levels, enhanced plasma levels of soluble P-selectin, and had no significant effect on platelet aggregation. Aspirin plus clopidogrel therapy made no difference to the plasma markers of thrombogenesis or platelet activation, but the platelet aggregation responses to adenosine diphosphate and epinephrine were decreased. Thus, the authors concluded that association of aspirin plus clopidogrel failed to reduce plasma indexes of thrombogenesis and platelet activation in atrial fibrillation, although some aspects of ex vivo platelet aggregation were altered. They considered that anticoagulation with warfarin may be superior to combination of aspirin plus clopidogrel as thromboprophylaxis in atrial fibrillation.