Cumulative antiplatelet effect of low‐dose enteric coated aspirin

Abstract

Enteric coated aspirin (ECA) at doses of 325–1300 mg is an effective alternative to regular aspirin for inhibition of platelet activity while avoiding gastric irritation. The objectives of this study were to determine: (1) the lowest chronic dose of ECA providing effective inhibition of platelet activities, (2) the time course of the inhibition, and (3) the reappearance of platelet cyclo-oxygenase activity. Seven subjects were studied before and after seven daily doses of 40–325 mg ECA. Serum thromboxane (TX) B₂ levels indicated that the lowest dose of ECA resulting in greater than 90% inhibition of platelet cyclo-oxygenase was 80 mg/d. Platelet aggregation and ATP release in response to collagen (1 μg/ml) and arachidonic acid (1 mM) were abolished and bleeding times were prolonged from 6.1 ± 1.5 min to 9.7 ± 2.8 min (mean ± SD, P2 had decreased by approximately 60% and was suppressed by more than 90% after four doses. Recovery of platelet cyclo-oxygenase activity after a single 80 mg dose of ECA was delayed for 48–72 h indicating that aspirin reached the systemic circulation. We conclude that chronic inhibition of platelet activity may be achieved in a cumulative manner with 80 mg ECA/d.