Question
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- (a) Explain the mechanism of action, uses and adverse effects of Aspirin. ( 4 mark(s)
- (b) Briefly describe Low molecular weight Heparin. 4 mark(s)
Answer
a) Aspirin — mechanism, uses, adverse effects Mechanism: irreversibly acetylates and inhibits cyclooxygenase (COX-1 and COX-2), blocking prostaglandin and thromboxane A2 synthesis. At low doses, this predominantly and durably suppresses platelet thromboxane A2 (platelets cannot resynthesize COX), giving an antiplatelet effect; at higher doses, COX inhibition throughout the body gives analgesic, antipyretic, and anti-inflammatory effects. Uses: analgesia, antipyresis, anti-inflammatory use (at high dose), antiplatelet prophylaxis (low dose — secondary prevention of MI/stroke). Adverse effects: GI irritation/peptic ulceration, increased bleeding risk, hypersensitivity/bronchospasm in aspirin-sensitive asthmatics, Reye’s syndrome (avoided in children with viral illness), salicylism/toxicity in overdose.
b) Low molecular weight heparin Fragments of unfractionated heparin with a shorter chain length, giving a more predictable dose-response, longer half-life (permitting once/twice-daily subcutaneous dosing), and no need for routine aPTT monitoring. Mechanism: binds antithrombin III and predominantly inactivates factor Xa (comparatively less effect on thrombin/IIa than unfractionated heparin, since it is too short to bridge thrombin and antithrombin simultaneously). Uses: prophylaxis/treatment of deep vein thrombosis and pulmonary embolism, acute coronary syndrome, and safe use in pregnancy. Adverse effects: bleeding, lower incidence of heparin-induced thrombocytopenia than unfractionated heparin; protamine only partially reverses its effect.