February 2026
M	T	W	T	F	S	S
	1
2	3	4	5	6	7	8
9	10	11	12	13	14	15
16	17	18	19	20	21	22
23	24	25	26	27	28

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

Immediate action
Injectable
Acts via Antithrombin III
Monitored by aPTT
Safe in pregnancy
Short half-life
Used for acute cases

Warfarin

Delayed action
Oral
Blocks vitamin K factors
Monitored by PT / INR
Unsafe in pregnancy
Long half-life
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