Aspirin and other platelet-aggregation inhibiting drugs.

The biochemistry of platelets is surprisingly complex, and offers the opportunity for numerous platelet-aggregation inhibiting ("antiplatelet") drugs to interfere with different aspects of their metabolism and function. Thus, aspirin inhibits platelet aggregation by irreversibly inactivating cyclo-oxygenase, a key enzyme in platelet prostaglandin metabolism, while the other nonsteroidal anti-inflammatory drugs and sulphinpyrazone cause reversible and dose-dependent inhibition of the same enzyme. Dipyridamole can inhibit both platelet adhesion and aggregation by raising the platelet cyclic AMP level through phosphodiesterase inhibition. The use of aspirin, sulphinpyrazone, and dipyridamole as antithrombotic agents has now been extensively evaluated. In general, treatment with these drugs has been more likely to prevent arterial than venous thromboembolism, and aspirin or the combination of aspirin and dipyridamole has been more effective in this respect than has sulphinpyrazone. Recent evidence strongly suggests that aspirin reduces the risk of non-fatal myocardial infarction in patients with unstable angina, and that the administration of aspirin in combination with dipyridamole significantly improves graft patency after aortocoronary bypass. Aspirin also appears to reduce the likelihood of stroke or death in men with transient cerebral ischaemic attacks.