UNCONTROLLED WHEN PRINTED
Introduction
  • Utilised for prophylaxis and treatment of venous thrombosis and it’s extension, prevention pf post-operative deep vein thrombosis, pulmonary embolism and prevention of clotting in arterial and cardiac surgery.
  • Heparin is prescribed to prevent embolisms in patients with unstable angina or non-Q wave myocardial infarctions.  
Mechanism of Action
  • Antithrombin III inactivates thrombin and factor Xa.
  • Administered heparin binds reversibly to antithrombin III and leads immediately to inactivation of factors IIa and Xa.
  • Acts mainly by accelerating the rate of the neutralisation of certain activated coagulation factors by antithrombin, but other mechanisms may be involved.
  • The antithrombic effect of heparin is well correlated to the inhibition of fator Xa.
  • Prevents progression of existing clots by inhibiting further clotting.
Adverse effects
  • Increased bruising
  • Increased bleeding time
  • Increased liver enzyme readings
  • Severe affects could include internal bleeding
Precautions
Drug Interactions

Some interaction include but are not limited to:

  • Pain relief medication including aspirin as they have anticoagulation effects
  • A select few medications used for heart and circulation problems including GTN and digitalis
  • Anti-clotting medications such as Warfarin, Dectran and alteplase
Overdose
  • The median lethal dose is 5000mg/kg. It induces Heparin induced thrombocytopenia (HIT). HIT is caused by an immune response that makes platelets from clots within the vessels using coagulation factors. It can also cause arterial thrombosis, gangrene, stroke, myocardial infarction and disseminated intravascular coagulation.
  • Symptoms of an overdose include excessive prolongation of aPTT or bleeding. 
Pharmacology

Pharmacokinetics

Absorption
  • Preferred method of administration is IV however can be administered subcutaneously. IV absorption and onset is immediate peak concentration is immediate. Subcutaneous action onset is between 20-60 minutes.
Distribution
  • Heparin binds to clotting factors antithrombin and fibrinogens. Components such as lipoproteins, proteases and globulins are also sites of heparin binding. All transported through the body though the venous system.
Metabolism
  • Liver and the reticulo-endothelial system are the sites of biotransoformation.
Elimination

Pharmacodynamics

Intended activity
Therapeutic window
  • Typical half-life is 90 minutes.
  • Plasma half-life of heparin increases from:
    • 60 minutes with a 40unit/kg dose
    • 150 minutes with a 100 unit/kg dose
Duration of action
  • Action is immediate following IV administration and is effective for 3-6 hours

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