Thienopyridine therapy and risk for cardiovascular events in secondary prevention.

Platelets are critical modulators of atherothrombotic events. In the acute setting, platelets are activated and aggregate on the surface of atherosclerotic plaque that has ruptured, fissured, or developed erosions. The overlying thrombus leads to sudden development of arterial luminal obstruction, inducing ischemia and cellular necrosis. Inhibiting platelet reactivity is an important therapeutic goal in patients at risk for acute cardiovascular events. The thienopyridines are potent inhibitors of platelet aggregation and block the binding of adenosine 5'-diphosphate to purinergic receptors on the surface of the platelet membrane. The thienopyridine class includes ticlopidine, clopidogrel, and prasugrel. Clopidogrel is the most intensively studied. In recent years it has become apparent that approximately 20% to 25% of patients who would be expected to benefit from clopidogrel therapy are resistant to this drug, largely due to a polymorphism in the gene for cytochrome P450 2C19. The efficacy of clopidogrel can also be reduced if patients are receiving concomitant therapy with a proton pump inhibitor such as omeprazole. Prasugrel is a third-generation thienopyridine with faster time to onset and greater consistency in inhibiting platelet activity, and it has shown superiority to clopidogrel for reducing cardiovascular events in patients with acute coronary syndromes undergoing percutaneous coronary interventions.