Tranexamic acid (TXA) is administered to a trauma patient. What is its mechanism of action and critical time window for administration?
- A Inhibits thrombin formation; must be given within 6 hours of injury
- B Activates protein C to prevent coagulopathy; effective up to 12 hours after injury
- C Competitively inhibits plasminogen binding to fibrin (antifibrinolytic); maximum benefit within 3 hours; administration after 3 hours may increase mortality ✓
- D Inhibits von Willebrand factor degradation; effective only in haemophilia patients
Correct answer: C. Competitively inhibits plasminogen binding to fibrin (antifibrinolytic); maximum benefit within 3 hours; administration after 3 hours may increase mortality
Explanation
Tranexamic acid is a lysine analogue that competitively inhibits the binding of plasminogen to fibrin, thereby preventing fibrin degradation (antifibrinolytic mechanism). The CRASH-2 trial demonstrated that TXA given within 1 hour reduces death by 32%; within 1–3 hours by 20%; but administration after 3 hours was associated with increased risk of fatal haemorrhage (possibly from worsening clot lysis). It has no effect on coagulation factor activity. The WOMAN trial confirmed benefit in postpartum haemorrhage within 3 hours of birth.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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