Effect of acetaminophen and salicylate on aspirin-induced inhibition of human platelet cyclo-oxygenase.

Recent studies have shown that salicylic acid, a metabolite of aspirin, effectively competes for the same site on the platelet cyclo-oxygenase enzyme. In the present investigation we have evaluated the effect of salicylate and acetaminophen on aspirin induced inhibition of cyclo-oxygenase and platelet function. Results of our studies show that both drugs at equimolar concentrations had no inhibitory effect on aspirin induced blockage of cyclo-oxygenase or platelet function. Even at higher concentrations acetaminophen failed to protect cyclo-oxygenase or prevent inhibition of platelet function by aspirin. Salicylate at concentrations above 5 mM effectively blocked the inhibition of cyclo-oxygenase activity and platelet aggregation in response to arachidonate.