One of the most important trials comparing anticoagulation versus antiplatelet (aspirin) therapy in patients with AFib was the Apixaban versus Acetylsalicylic Acid to Prevent Strokes in Atrial Fibrillation Patients Who Have Failed or Are Unsuitable for Vitamin K Antagonist Treatment (AVERROES) trial.[6]  This addressed the question of whether patients with AFib can ethically be enrolled in a randomized trial where for some reason the patient or the physician feels warfarin would not be the drug of choice. (The reason might have been because the patient refused warfarin or because the patient lives at a great distance and cannot be monitored on warfarin.)  All patients were randomized to either the factor Xa inhibitor apixaban or aspirin, and unsurprisingly the trial was stopped early due to the benefit and efficacy with apixaban. 

Figure 8 illustrates the other major finding of this trial, the fact that the major bleeding was nearly identical, with a relative risk (RR) of 1.18, P=0.76.  In other words, in this population apixaban and aspirin were associated with almost the same amount of major bleeding.  What Figure 8 shows is not necessarily that apixaban is safer, but rather that aspirin is not as harmless as many believe it is.  This is because there are changes in the guts of older patients that render them more susceptible to the deleterious effects of aspirin (or antiplatelet) therapy.