Makindo Medical Notes

Low Molecular Weight Heparin (LMWH): Used in both the prevention and treatment of thrombosis.
Always consult the BNF or equivalent local guidelines for precise dosing and monitoring recommendations.

Overview

• LMWH is derived from standard (unfractionated) heparin by controlled depolymerisation or enzymatic breakdown.
• Has a more predictable anticoagulant response compared to unfractionated heparin (UFH) due to its targeted anti–Factor Xa activity.
• Enables weight-adjusted dosing and can often be administered without routine laboratory monitoring in patients with normal renal function.
• Renally excreted: dose adjustment is required in renal impairment.

Mechanism of Action

• Primarily enhances the inactivation of Factor Xa via binding to antithrombin.
• Less effect on thrombin (Factor IIa) compared to UFH.
• Given subcutaneously; not reversed easily by protamine (only partial antagonism).

Cautions & Contraindications

• Conditions predisposing to bleeding:
  • Thrombocytopenia, haemophilia, severe liver failure, severe renal impairment.
  • Marked hypertension (e.g., systolic >200 mmHg or diastolic >120 mmHg).
  • Active peptic ulcer, oesophageal varices, aneurysm, proliferative retinopathy.
  • Recent organ biopsy, head/orbit/spinal surgery, recent stroke.
  • Confirmed intracranial or intraspinal bleed.
• Heparin-Induced Thrombocytopenia (HIT) or Thrombosis: history of HIT is a contraindication; requires alternative anticoagulation.

Monitoring

• Routine anti–Factor Xa assays are generally unnecessary unless:
  • Renal failure or significant renal impairment.
  • Unusual bleeding, thrombosis extension, or overdose suspected.
  • Extreme body weights (<40 kg or >150 kg) in some protocols.
• Monitor platelet count to detect HIT; a marked drop in platelets warrants urgent investigation.

Common Formulations

• Enoxaparin (US brand name: Lovenox)
• Tinzaparin
• Dalteparin (another widely used LMWH)
• Fondaparinux (synthetic Factor Xa inhibitor; not strictly an LMWH but often used similarly)

Side Effects

• Bleeding: Can be serious; protamine sulfate only partially reverses LMWH.
• Hyperkalaemia: LMWH can reduce aldosterone secretion, leading to elevated potassium levels.
• Thrombocytopenia:
  • HIT occurs in up to 5% of cases, more frequently with prolonged therapy.
  • Suspected HIT requires cessation of all forms of heparin and urgent haematology consultation.
• Osteoporosis (with prolonged use >20 weeks).