Which of the following drug inhibits aggregation of platelets: September 2005

Ans. D: Aspirin Aspirin's ability to suppress the production of prostaglandins and thromboxanes is due to its irreversible inactivation of the cyclooxygenase enzyme. Cyclooxygenase is required for prostaglandin and thromboxane synthesis. Aspirin acts as an acetylating agent where an acetyl group is covalently attached to a serine residue in the active site of the PTGS enzyme. This makes aspirin different from other NSAIDs (such as diclofenac and ibuprofen), which are reversible inhibitors. Very low-dose, long-term aspirin use irreversibly blocks the formation of thromboxane A2 in platelets, producing an inhibitory effect on platelet aggregation. This anticoagulant propey makes aspirin useful for reducing the incidence of hea attacks. 40 mg of aspirin a day is able to inhibit a large propoion of maximum thromboxane A2 release provoked acutely, with the prostaglandin 12 synthesis being little affected; however, higher doses of aspirin are required to attain fuher inhibition The main undesirable side effects of aspirin are gastrointestinal ulcers, stomach bleeding, and tinnitus, especially in higher doses. In children and adolescents, aspirin is no longer used to control flu-like symptoms or the symptoms of chickenpox or other viral illnesses, because of the risk of Reye's syndrome. Tranexaemic acid, EACA and aprotinin are antifibrinolytic drug