Heparin: Mechanism of Action
Heparin is an anticoagulant that prevents blood clot formation and is used to treat or prevent deep vein thrombosis, pulmonary embolism, and atrial fibrillation.
Anticoagulants inhibit clot formation through distinct mechanisms: VKA-mediated factor depletion, direct thrombin/Xa inhibition, or antithrombin-III activation.
How It Works
Anticoagulants act at different points in the coagulation cascade. Warfarin (VKA) inhibits VKORC1, depleting active vitamin K required for γ-carboxylation of factors II, VII, IX, X and proteins C and S. DOACs: apixaban, rivaroxaban, edoxaban directly inhibit Factor Xa; dabigatran directly inhibits thrombin (Factor IIa). Heparins (unfractionated and LMWH): bind antithrombin III, accelerating its inhibition of thrombin and Factor Xa by ~1,000-fold. LMWHs (enoxaparin, dalteparin) have more predictable pharmacokinetics and higher Xa:IIa inhibition ratio than unfractionated heparin.
Receptor / Target Profile
- •VKORC1 (vitamin K epoxide reductase complex 1) — warfarin target
- •Factor Xa — apixaban, rivaroxaban, edoxaban, enoxaparin, dalteparin
- •Thrombin (Factor IIa) — dabigatran, unfractionated heparin (indirect via antithrombin)
- •Antithrombin III — heparin/LMWH co-factor; catalytic activation accelerates ~1,000×
- •CYP2C9, VKORC1 — genetic variants determining warfarin dose requirements
Pharmacokinetics
Onset of Action
Warfarin: 2–5 days to therapeutic INR; DOACs: anticoagulant effect within 1–3 hours; IV heparin: immediate; LMWH: 3–5 hours (subcutaneous)
Half-Life (t½)
Warfarin: 36–42 hours; Apixaban: 12 hours; Rivaroxaban: 5–9 hours; Dabigatran: 12–17 hours; Enoxaparin: 4–7 hours; IV heparin: 30–90 minutes
DOACs: oral bioavailability 50–80% (dabigatran ~6% — prodrug dabigatran etexilate); renal elimination 25–80% (dabigatran ~80%). Warfarin: ~100% oral bioavailability; narrow therapeutic index (INR 2–3). DOACs do not require routine monitoring.
Conditions Treated with Heparin
Questions about your medication?
Our AI Symptom Checker analyses your symptoms and suggests the most likely diagnoses — including relevant medications.
Use AI Symptom Checker →