Unfractionated heparin exerts its anticoagulant action through which mechanism?

• A Direct inhibition of thrombin by occupying its active site
• B Inhibition of phosphodiesterase, raising platelet cAMP
• C Competitive antagonism of vitamin K epoxide reductase
• D Acceleration of antithrombin-mediated inhibition of thrombin and factor Xa ✓

Explanation

Heparin is an indirect anticoagulant: it binds antithrombin (antithrombin III) through a specific pentasaccharide sequence and induces a conformational change that accelerates antithrombin's inactivation of thrombin (IIa) and factor Xa several thousand-fold. Direct active-site inhibition defines drugs like argatroban and dabigatran. Vitamin K antagonism defines warfarin, and PDE inhibition with raised cAMP describes dipyridamole and cilostazol. Antithrombin deficiency therefore causes clinical heparin resistance.

Reference: Katzung Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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