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Tareq Abadl: Heparin vs Warfarin
Tareq Abadl/LinkedIn
Feb 2, 2026, 17:08

Tareq Abadl: Heparin vs Warfarin

Tareq Abadl, Medical Laboratory Specialist and Director of the Blood Bank at Dr. Abdelkader Al-Mutawakkil Hospital, shared a post on LinkedIn:

“Heparin vs Warfarin – Anticoagulant Therapy.

Both Heparin and Warfarin are blood thinners used to prevent or treat clots, but they differ greatly in mechanism, onset, route, monitoring, and safety.

HEPARIN

  • What it is

• Fast-acting injectable anticoagulant

  •  Mechanism of action

• Enhances Antithrombin III
• Inhibits Thrombin (Factor IIa) and Factor Xa

(• Result: immediate prevention of clot extension)

     • Onset and duration

• IV: immediate
• Subcutaneous: 1–2 hours
• Short half-life (~1–2 hours)

  • Route

• IV or Subcutaneous

  •  Monitoring

• aPTT

      • Main uses

• Acute DVT / PE
• Acute coronary syndromes
• Peri-operative anticoagulation
• Bridging to warfarin
• Safe anticoagulation in pregnancy

  • Important points

• Does NOT cross placenta
• Preferred in pregnancy
• Used mainly for acute settings

  • Major adverse effects

• Bleeding
• Heparin-Induced Thrombocytopenia (HIT)
• Osteoporosis (long-term use)

  •  Antidote

• Protamine sulfate

WARFARIN

  • What it is

• Oral anticoagulant
• Vitamin K antagonist

  • Mechanism of action

• Inhibits Vitamin K epoxide reductase
• Decreases synthesis of clotting factors: II, VII, IX, X
• Also reduces Protein C & Protein S initially

(• Result: delayed anticoagulant effect)

  •  Onset

• 36–72 hours (delayed)

  •  Route

• Oral

  • Monitoring

• INR
Target INR usually 2–3

  • Main uses

• Long-term anticoagulation
• Atrial fibrillation
• Mechanical heart valves
• Chronic DVT / PE prevention
• Stroke prevention

  •  Important points

• Crosses placenta
• Teratogenic
• Contraindicated in pregnancy
• Requires frequent INR monitoring
• Many food & drug interactions

  • Major adverse effects

• Bleeding
• Skin necrosis (early due to Protein C depletion)
• Purple toe syndrome
• Fetal warfarin syndrome (if used in pregnancy)

  • Antidote

• Vitamin K
• PCC or FFP for severe bleeding

Key Differences (Exam Favorite)

Heparin

  1. Immediate action
  2. Injectable
  3. Acts via Antithrombin III
  4.  Monitored by aPTT
  5. Safe in pregnancy
  6. Short half-life
  7.  Used for acute cases

Warfarin

  1.  Delayed action
  2. Oral
  3. Blocks vitamin K factors
  4. Monitored by PT / INR
  5. Unsafe in pregnancy
  6.  Long half-life
  7. Used for chronic therapy

 Bridging Therapy (Very Important)

  • Heparin is started first
  • Warfarin added simultaneously
  • Heparin stopped only after INR becomes therapeutic

Reason:
Warfarin initially reduces Protein C to temporary hypercoagulable state

Relationship Between Heparin and Warfarin and Coagulation Tests (PT and aPTT)

Heparin primarily affects the Intrinsic pathway by enhancing Antithrombin III and inhibiting Thrombin and Factor Xa.
• This leads to prolongation of aPTT.
• PT is usually normal.

Warfarin primarily affects the Extrinsic pathway, especially Factor VII, by inhibiting vitamin K–dependent clotting factor synthesis.
• This leads to prolongation of PT and elevation of INR.
• aPTT is usually normal or only mildly prolonged.

High-yield exam rule:

Heparin to aPTT
Warfarin to PT / INR”

 

Tareq Abadl: Heparin vs Warfarin

More posts from Tareq Abadl on Hemostasis Today.

Anticoagulant Therapy Anticoagulation Antithrombin III Health Hematology Hemostasis Hemostasis News Hemostasis Today Heparin Tareq Abadl Warfarin
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