Aspirin (ASA), the most commonly used antiplatelet agent, prevents stroke recurrence among patients with a recent stroke or transient ischemic attack (TIA). In a meta-regression analysis of placebo controlled trials of ASA therapy for secondary stroke prevention, the relative risk reduction for stroke was estimated at 15% (95% CI, 6% to 23%) . However, clinical and laboratory evidence demonstrates diminished or no response to ASA in some patients that is called ASA resistance. This situation has been reported to be independently associated with an increased risk of adverse cardiovascular events: ASA resistance is associated with increased clinical severity and stroke infarct volume in acute stroke patients, increased the rate of recurrent stroke and other vascular events, and is also linked with short and long term mortality in these patients .
