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Hematology Anticoagulation Pharmacology Intermediate
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Coagulation Pathways & Antidotes: Warfarin vs Heparin

EX-PRESIDENT
vs
IN-SIDE
Essential clinical cheat sheet distinguishing Warfarin (Extrinsic / PT) from Heparin (Intrinsic / aPTT).

Warfarin inhibits Vitamin K epoxide reductase (VKORC1), blocking carboxylation of factors II, VII, IX, X, Protein C, and Protein S. Heparin binds antithrombin III to accelerate neutralization of thrombin and factor Xa.

Systematic Breakdown

Warfarin

WEPT: Warfarin Extrinsic Pathway PT/INR

Warfarin affects Extrinsic pathway first (Factor VII has shortest half-life ~6h); monitored via PT / INR. Antidote: Vitamin K1 (Phytonadione) + 4-Factor PCC (Kcentra) for urgent reversal.

Heparin

Heparin = INtrinsic Pathway = aPTT

Unfractionated Heparin enhances Antithrombin III; monitored via aPTT (prolongs intrinsic cascade). Antidote: Protamine Sulfate (1 mg reverses ~100 units heparin).

Teratogen

Warfarin = Teratogen; Heparin = Safe in Pregnancy

Warfarin crosses placenta causing fetal chondrodysplasia punctata and bone deformities; Heparin is large and water-soluble (does NOT cross placenta).

Skin Necrosis

Warfarin Skin Necrosis Risk

Protein C has short half-life (~8h); starting warfarin without heparin bridge causes transient hypercoagulable state and microvascular thrombosis.

High-Yield Clinical Pearls & Exam Tips
  • Always bridge with Heparin when starting Warfarin in acute thrombosis until INR is therapeutic (2.0 - 3.0) for at least 24-48 hours.
  • LMWH (Enoxaparin) predominantly inhibits Factor Xa and does NOT require routine aPTT monitoring (use anti-Xa levels if renal failure or obesity).
Related Pharmaceuticals
Warfarin Heparin Enoxaparin Protamine Sulfate Phytonadione (Vitamin K1)
Related Clinical Conditions
Deep Vein Thrombosis Pulmonary Embolism Heparin-Induced Thrombocytopenia (HIT)
Authoritative Sources: Katzung Basic & Clinical Pharmacology 15e · CHEST Antithrombotic Guidelines

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