Overview
Heparin is a naturally occurring anticoagulant that prevents the formation and extension of blood clots. It is a glycosaminoglycan that enhances the activity of antithrombin III, which inactivates thrombin and other clotting factors. Heparin sodium is the most commonly used form, administered parenterally for rapid anticoagulation in various clinical settings.
Mechanism of Action
Heparin binds to antithrombin III (AT III), causing a conformational change that accelerates its inhibition of thrombin (Factor IIa) and Factor Xa. This prevents the conversion of fibrinogen to fibrin and inhibits thrombus formation and extension. Heparin's anticoagulant effect is immediate upon intravenous administration.
Indications
- Prophylaxis and treatment of venous thrombosis and pulmonary embolism
- Prevention of clotting during cardiac and vascular surgery
- Prevention of clotting in extracorporeal circulation (e.g., hemodialysis, cardiopulmonary bypass)
- Treatment of acute coronary syndromes (unstable angina, myocardial infarction)
- Prevention of clotting in indwelling catheters
Dosage
Dosage is highly individualized based on patient weight, indication, and monitoring of activated partial thromboplastin time (aPTT) or anti-Xa activity. Typical initial IV bolus: 80 units/kg, followed by continuous infusion of 18 units/kg/hour. Subcutaneous administration: 5,000 units every 8-12 hours for prophylaxis. Adjust based on laboratory monitoring.
Contraindications
- Hypersensitivity to heparin or pork products
- Active major bleeding
- Severe thrombocytopenia
- Uncontrolled hypertension
- Recent or planned surgery of the eye, brain, or spinal cord
- Subacute bacterial endocarditis
Side Effects
- Bleeding (most common)
- Heparin-induced thrombocytopenia (HIT)
- Elevated liver enzymes
- Local reactions at injection site
- Osteoporosis with long-term use
- Hypersensitivity reactions
- Alopecia
- Skin necrosis
Interactions
- Oral anticoagulants (warfarin) - increased bleeding risk
- Anti-platelet drugs (aspirin, clopidogrel) - increased bleeding risk
- Thrombolytics (alteplase) - increased bleeding risk
- NSAIDs - increased bleeding risk
- Digoxin, tetracyclines, nicotine - may decrease heparin effect
- Antihistamines, digitalis, tetracyclines - may interfere with anticoagulant monitoring