Acetylsalicylic acid (ASA) - How much, how often, and when? A clinical-pharmacological perspective.

The dose of acetylsalicylic acid (ASA) commonly used in the prevention and treatment of arteriosclerotic angiopathies is equal to or less than 100 mg daily. This choice of dose is predominantly based on molecular-pharmacological findings showing an inhibition in synthesis of the prothrombotic thromboxane (TXB2) and an irreversible inhibition in blood platelet aggregation. However, an analysis of ASA dose-effect relationships for doses of 50 - 500 mg (PO and IV) shows that doses of ASA up to 100 mg daily produce only a small or moderate inhibition in collagen/epinephrine-induced platelet aggregation and have no significant effect on the important platelet factors, PF3 and PF4. Doses of ASA 300 - 500 mg, on the other hand, inhibit platelet aggregation almost completely and, in addition, produce a 50 - 70% inhibition in PF3 and PF4 lasting at least 24 hours. There is also evidence that doses of ASA above 100 mg daily markedly inhibit thromboxane synthesis for up to 24 hours and that doses of 500 mg daily produce a clinically relevant inhibition in platelet adhesion to vessel walls for up 72 hours and prevent procoagulatory shape changes for up to 12 hours. These findings suggest that a dose of ≥ 300 mg at intervals of 2 - 3 days would be more appropriate for primary and secondary prophylaxis of arteriosclerotic angiopathies and that the benefit-risk ratio would be greater because of the increased availability of mucoprotective prostaglandins, PGI2 (prostacyclin) and the gastroprotective, PGE2. Our viewpoint, predominantly based on findings with biomarkers, could serve as a basis for further randomized controlled studies.