Aspirin and Platelets

Once the relevance of platelets to thrombosis came to be generally accepted, pharmacologists and others began to take an interest in platelet active drugs. The initial search was for drugs that would affect platelet stickiness but the development of the aggregometer, and the very much more reproducible measurements that this gave, greatly facilitated research on drug effects.

O’Brien, a pathologist in Portsmouth, was active in this field from the early 1960’s, and now, aged 80 years, he is still working on platelets!

O’Brien reported the platelet effects of a large range of drugs, including several salicylates. (16) He judged however that the doses of most of the drugs he tested which would be sufficient to significantly alter platelet function, would probably be lethal.17 An effect of aspirin on platelets was first described by Morris in 1967.18

O’Brien and others immediately took this up and showed that reductions in the dose of aspirin, down to 150 mg lost none of the platelet anti-aggregant effects.(19) It was also shown that the effect of a single dose is detectable on platelet aggregation for a period of days - in fact, for up to ten days by which time all the affected platelets have been replaced. (20)