Describe the pharmacology of tranexamic acid.
Tranexamic acid is a drug used to reduce bleeding in trauma or surgery. It is also used for hereditary angioedema and menstrual bleeding. It is being increasingly used in critically ill patients. As a Level B listed drug within the Primary Syllabus candidates would be expected to know it in some depth. Often basic information such as mechanism of action, pharmacokinetics and adverse effects was lacking.
|Class||Serine protease inhibitor|
|Chemistry||Monocarboxylic acid (a synthetic derivative of the amino acid lysine)|
|Routes of administration||IV, nebulised, topical, oral|
|Absorption||50% absorbed from the GI tract; bioavailability is about 30-35%. Most of it is not metabolised.|
|Solubility||pKa of 10.22; highly water-soluble, but minimally fat-soluble|
|Distribution||VOD = 0.18 L/kg; minimally protein-bound (3%, all of which is accounted for by its binding to plasminogen). After some loading (eg. several doses over 24-36 hrs), enough of it distributes to the tissues to continue having a sustained antifibrinolytic effect for many hours.|
|Elimination||95% of the dose is excreted unchanged in the kidneys; half-life is 2 hours|
|Time course of action||Relatively short-acting, very rapid onset of effect|
|Mechanism of action||Competitive inhibitor of plasminogen activation (by binding to the 5-lysine site on plasminogen). This inhibits the formation of plasmin and displaces plasminogen from the surface of fibrin.|
|Clinical effects||Prevents the breakdown of fibrin, thus maintaining clot integrity. Numerous other effects (as it also inhibits other proteases), as well as indirect effects via plasminogen inhibition (eg. on complement activation, where by reducing plasmin activity it reduces the consumption of C1 esterase inhibitor)|
|Single best reference for further information||Data sheet from medsafe.govt.nz|
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