Makindo Medical Notes

Heparin: two main types — unfractionated (UFH) and low molecular weight heparin (LMWH).

About: Always check the BNF or equivalent for specific prescribing advice.

• Used in both prevention and treatment of thrombosis.
• Consists of polysaccharides derived from porcine gastric mucosa.

Types of Heparin

• Unfractionated Heparin (UFH)
  • A mixture of naturally occurring glycosaminoglycans; molecular weight ranges from 5,000 to 30,000.
  • Usually administered intravenously (IV).
  • Effect can be reversed by stopping the infusion and administering protamine sulphate.
• Low Molecular Weight Heparin (LMWH)
  • Produced from unfractionated heparin by controlled depolymerisation; typical molecular weight ~4,000 to 6,500.
  • Administered subcutaneously (SC), often once or twice daily depending on indication.
  • Longer half-life, and more difficult to reverse. Protamine only partially neutralises its effects.

Cautions

Use with caution in conditions or situations that increase bleeding risk or complicate heparin therapy, including:

• Thrombocytopenia, haemophilia, significant liver or renal failure.
• Severely elevated blood pressure (e.g., systolic > 200 mmHg or diastolic > 120 mmHg).
• Active peptic ulcer, oesophageal varices, aneurysm, proliferative retinopathy, recent organ biopsy.
• Recent major trauma or surgery involving the head, orbit, or spine; recent stroke.
• Confirmed intracranial or intraspinal bleeding.
• History of heparin-induced thrombocytopenia (HIT) or thrombosis.

Mechanism of Action

• All heparins bind to antithrombin III (AT III), enhancing its ability to inactivate thrombin and factor Xa, thus inhibiting coagulation.
• LMWHs also have notable anti-IIa (thrombin) activity, but are primarily known for their anti-Xa effects.

Management of Side Effects

• Bleeding:
  • Stop heparin; give protamine (full or partial reversal depending on UFH vs LMWH).
  • Consider blood product transfusion if significant blood loss.
  • Seek haematology advice if bleeding is severe or persistent.
• Heparin-Induced Thrombocytopenia (HIT):
  • Occurs in up to 5% of patients, more common with prolonged treatment.
  • Stop all forms of heparin immediately; involve haematology for alternative anticoagulation (e.g., direct thrombin inhibitors).
• Hyperkalaemia: Heparin can reduce aldosterone secretion, causing elevated potassium levels.
• Osteoporosis: Risk increases with long-term or high-dose use.