EFFECTS OF LOW-DOSE ASPIRIN ON IN-VITRO PLATELET-AGGREGATION IN THE EARLY MINUTES AFTER INGESTION IN NORMAL SUBJECTS

Aspirin interferes with platelet aggregation by inhibiting the metabol ism of arachidonic acid to thromboxane A(2). Although both high- and l ow-dose aspirin therapies are effective for secondary prophylaxis in p atients with atherosclerotic vascular disease, the acute response to l ow-dose aspirin therapy is controversial. Eighteen volunteer subjects ingested 81, 162, or 324 mg of aspirin in a longitudinal crossover stu dy design. Initial doses were randomly assigned and dosing intervals w ere separated by 2 weeks. Platelet aggregation in response to 0.9 mM a rachidonic acid was measured at baseline, 15, 30, 60, and 90 minutes a fter ingestion. Thromboxane B-2 production was assayed on simultaneous ly obtained samples after stimulation with arachidonic acid. The media n inhibition of aggregation was 97%, 97%, and 97% 15 minutes after ing estion of 81, 162, and 324 mg, respectively. Four subjects had <20% in hibition 15 minutes after ingesting 81 mg, but all 4 had >90% inhibiti on after 30 minutes. Thromboxane B-2 production declined by >93% in al l subjects at each dose. There was no difference between doses in inhi bition of thromboxane B-2 production.