Aspirin is an antiplatelet drug, inhibiting the cyclooxygenase activity of platelet prostaglandin H synthase-1 and almost complete
suppressing platelet capacity to generate the prothrombotic and proatherogenic thromboxane A2. Antiplatelet therapy with aspirin
reduces the risk of serious vascular events by about a quarter in patients who are at high risk because they already have occlusive vascular
disease. However, the inhibition of thromboxane-dependent platelet function by aspirin is effective for the prevention of thrombosis, but
is also associated with excess bleeding, although the absolute increase in major gastrointestinal or other major extracranial bleeds is an
order of magnitude smaller. For secondary prevention of vascular events, the benefits of aspirin therapy substantially exceed the risks.
Therefore, aspirin is a cornerstone of antithrombotic therapy in acute coronary syndromes, in chronic ischemic heart disease and in percutaneous
coronary intervention. On the other hand, the role of aspirin in primary prevention remains uncertain and it is still debated, because
the absolute risk of vascular complications is the major determinant of the absolute benefit of antiplatelet prophylaxis and the reduction
in vascular events needs to be weighed against any increase in major bleeds.
Future data from ongoing studies will help us to identify people at high vascular risk who take advantage from aspirin therapy for primary
prevention or will indicate if specific category of high risk patients, like patients with diabetes, could be better protected from an increase
in the frequency of aspirin administration.