Which one of the following statements is not true about NSAIDSs?
Ans. is 'c' i.e., Duration of action of aspirin is primarily related to pharmacokinetic clearance of the drug form the body Since Aspirin irreversibly inhibits the cyclooxygenase enzyme, its duration of action depends on the rate of synthesis of fresh enzyme.All other NSAIDs are reversible inhibitor of cyclo-oxygenase and thus their duration of action is related to their pharmacokinetic clearance from the body.NSAIDS possess a single mode of action which is to block prostaglandin synthesis by inhibiting the enzymes of the cyclooxygenase pathway i.e. Cox - 1 and Cox - 2.Platelets are especially susceptible to prolonged aspirin mediated, irreversible inactivation of cyclo oxygenase because they have little or no capacity for protein biosynthesis (as they are none nucleated) and thus they cannot regenerate the cyclo oxygenase enzyme as nucleated cell.In practical terms, this means that a single dose of Aspirin will inhibit the platelet cyclo oxygenase for the life of the platelet {8-11 days). A daily dose of Aspirin as small as 40 mg is sufficient to produce this effect.Aspirin (acetyl salicylic acid), is de acetylated in the liver to salicylic acid. In contrast to aspirin, salicylic acid has no acetylating capacity, so it cannot inhibit cyclo oxygenase.The ability of platelets to be inhibited by such low doses of aspirin is related to the presystemic inhibition of cyclo oxygenase in the portal circulation before aspirin is de acetylated to salicylate in die liver.Also know,The antiplatelet action of Aspirin is due to acetylation of cyclo oxygenase. This will prevent both thromboxane A2 and prostacyclin (PGI2) production.Therapeutic interest in antithrombotic effect of Aspirin has centred on separating its action on thromboxane A2 and prostacyclin formation and this can be achieved by using a low dose.Thus 75-100 mg/day of Aspirin is sufficient to abolish synthesis of thromboxane - A2 without significant impairment of prostacyclin formation.
Acetyl salicylic acid is an irreversible inhibitor of COX enyzme
Salicylic acid reduces in vivo synthesis of prostaglandins
Duration of action of aspirin is primarily related to the pharmocokinetic clearance of the drug from the body
Anitplatelet effect of low-dose aspirin is related to presystemic COX inhibition
Prostaglandins