Heparin

• Definition: Naturally occurring anticoagulant glycosaminoglycan produced mainly by mast cells.

• Function: Potentiates antithrombin III, which inactivates clotting factors IIa (thrombin) and Xa, preventing fibrin formation.

• Normal plasma concentration: ~0.1–0.2 µg/mL.

• Therapeutic use: Intravenous or subcutaneous administration for prevention/treatment of deep vein thrombosis (DVT), pulmonary embolism, and during cardiac surgeries.

• Key point: Immediate onset of action when given IV; reversed by protamine sulfate.