Paper I
2023 January (Supplementary) (2019 Scheme) · 100 marks · 180 min

Question

Heparin. (2+3+3)

Q78 marksShort Essays

Answer

Heparin is a naturally occurring sulfated glycosaminoglycan, extracted from porcine intestinal mucosa/bovine lung, and used clinically as a rapidly-acting parenteral anticoagulant.

Mechanism of action: heparin binds and potentiates antithrombin III (up to 1000-fold), which then inactivates thrombin (factor IIa) and factor Xa — unfractionated heparin inactivates both, while low molecular weight heparin acts predominantly on Xa. This prevents further clot propagation, though heparin has no direct effect on an already-formed clot.

Uses: prophylaxis and treatment of deep vein thrombosis/pulmonary embolism, acute coronary syndrome (adjunct to antiplatelet therapy), during surgery/cardiopulmonary bypass (rapid onset, reversible with protamine), pregnancy (does not cross the placenta, unlike warfarin).

Adverse effects: bleeding (the major risk, managed by dose reduction/protamine sulfate reversal), heparin-induced thrombocytopenia (immune-mediated, paradoxically prothrombotic), osteoporosis with long-term use, hypersensitivity reactions. Monitored via aPTT (unfractionated heparin); LMWH generally does not require routine monitoring given its more predictable dose-response.

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