Heparin is one of the most important anticoagulant drugs used in clinical medicine. It plays a vital role in the prevention and treatment of blood clots, especially in emergency and hospital settings. Because of its rapid action, heparin is widely used in cardiology, surgery, intensive care, and dialysis units.
This article explains what heparin is, how it works, its types, clinical uses, dosage, adverse effects, and key precautions, in a simple and student-friendly way.
What Is Heparin?
Heparin is a parenteral anticoagulant that prevents the formation and extension of blood clots. It is a naturally occurring glycosaminoglycan obtained from animal tissues such as porcine intestinal mucosa.
Unlike oral anticoagulants, heparin acts immediately when given intravenously, making it ideal for acute thrombotic conditions.
Classification of Heparin
Heparin is broadly classified into two main types based on molecular weight.
| Type | Full Form | Key Feature |
|---|---|---|
| Unfractionated Heparin (UFH) | — | Rapid action, requires monitoring |
| Low Molecular Weight Heparin (LMWH) | e.g., Enoxaparin | Predictable effect, less monitoring |
Mechanism of Action of Heparin
Heparin works by enhancing the activity of antithrombin III, a natural anticoagulant in the body.
Step-by-Step Mechanism
1. Heparin binds to antithrombin III
2. This complex inactivates:
- Thrombin (Factor IIa)
- Factor Xa
Key Exam Line
Heparin does not dissolve existing clots; it prevents clot extension and formation of new clots.
Types of Heparin Explained
1. Unfractionated Heparin (UFH)
- Large molecular size
- Given IV or subcutaneously
- Requires aPTT monitoring
- Short half-life
- Antidote available (protamine sulfate)
2. Low Molecular Weight Heparin (LMWH)
1. Smaller fragments of heparin- Enoxaparin
- Dalteparin
Clinical Uses of Heparin
Heparin is used in both preventive (prophylactic) and therapeutic settings.
Major Indications
- Deep vein thrombosis (DVT)
- Pulmonary embolism (PE)
- Acute coronary syndromes (MI, unstable angina)
- During cardiac surgery and bypass
- Hemodialysis
- Prevention of clotting in IV lines (Hep-lock)
Heparin Dose and Administration
Routes of Administration
- Intravenous (IV)
- Subcutaneous (SC)
⚠️ Heparin is never given intramuscularly due to bleeding risk.
General Dosing (UFH)
| Indication | Typical Dose |
|---|---|
| Acute thrombosis | IV bolus + infusion |
| Prophylaxis | Low-dose SC |
| Dialysis | Weight-based dosing |
Dose is adjusted based on aPTT levels.
Monitoring of Heparin Therapy
For UFH
- Activated Partial Thromboplastin Time (aPTT)
- Target: 1.5–2.5 times normal
For LMWH
- Routine monitoring not required
- Anti-Xa levels in special cases (pregnancy, renal failure)
Adverse Effects of Heparin
Common Side Effects
- Bleeding
- Bruising at injection site
- Thrombocytopenia
Serious Complications
Heparin-Induced Thrombocytopenia (HIT)
- Immune-mediated reaction
- Low platelet count with paradoxical thrombosis
- Requires immediate discontinuation
Others
- Osteoporosis (long-term use)
- Hyperkalemia (rare)
Contraindications of Heparin
Heparin should be avoided or used with caution in:
- Active bleeding
- Severe thrombocytopenia
- Recent brain or eye surgery
- Hemophilia or bleeding disorders
- Uncontrolled hypertension
Antidote for Heparin
Protamine Sulfate
- Specific antidote for unfractionated heparin
- Given intravenously
- Neutralizes heparin by forming an inactive complex
Heparin vs Warfarin (Quick Comparison)
| Feature | Heparin | Warfarin |
|---|---|---|
| Route | IV / SC | Oral |
| Onset | Immediate | Delayed |
| Monitoring | aPTT | INR |
| Use | Acute | Chronic |
| Antidote | Protamine sulfate | Vitamin K |
Special Precautions
- Avoid IM injections
- Monitor for bleeding signs
- Use caution in renal impairment (LMWH)
- Regular platelet count monitoring
Storage and Handling
- Store at room temperature
- Protect from light
- Use only under medical supervision
High-Yield Exam Points
- Rapid-acting anticoagulant
- Acts via antithrombin III
- Antidote: protamine sulfate
- Does not cross placenta (safe in pregnancy)
- Causes HIT
FAQs About Heparin
1. What is heparin mainly used for?
Heparin is used to prevent and treat blood clots, especially in conditions like DVT, pulmonary embolism, and heart attacks.
2. Can heparin dissolve existing clots?
No. Heparin prevents further clot formation and extension, but does not dissolve existing clots.
3. Why is aPTT monitored with heparin?
aPTT helps ensure the dose is therapeutic but not excessive, reducing bleeding risk.
4. Is heparin safe in pregnancy?
Yes. Heparin does not cross the placenta and is considered safe in pregnancy.
5. What is heparin-induced thrombocytopenia?
It is a serious immune reaction causing low platelets and increased clot risk.
6. Why is heparin not given intramuscularly?
IM injection can cause severe bleeding and hematoma formation.
7. What is the difference between UFH and LMWH?
UFH requires monitoring and has a short half-life, while LMWH has predictable action and fewer monitoring needs.
8. What is the antidote for heparin?
Protamine sulfate is the specific antidote for unfractionated heparin.
