Heparin

CLASS

  • anticoagulant
  • unfractionated heparin (UFH) is a sulfated polysaccharide with a molecular weight range of 3 to 30 kDa

MECHANISM OF ACTION

  • inhibits Factors IIa and Xa
  • binds reversibly to antithrombin III
    -> has a high affinity pentasaccharide binding site which is present in ~ 1/3 of heparin molecules
    -> conformational change
    -> 1000 times more potent inhibition of  these proteases in the coagulation cascade:
  • IIa (thrombin) and Xa primarily
  • also IX and IX
  • others: XII, XIII, plasmin
  • Maximal anti-IIa activity is dependent upon the binding of heparin to both thrombin and antithrombin III — molecules <18 saccharide units lack the necessary chain length to form a bridge between the two molecules and so short chain heparin molecules have primarily anti-Xa inhibitory activity
  • also binds directly to several coagulation proteases and thereby facilitates their reaction with antithrombin III
  • UFH binds to a number of plasma proteins and which accounts for the variable intra-individual anticoagulant response

PHARMACEUTICS

  • mixture of acid mucopolysaccharides extracted from bovine lung or porcine intestinal mucosa
  • clear colourless solution of Na-heparin (1000 to 25,000IU/mL)
  • heparin calcium (25,000IU/mL)
  • MW 3,000 to 30,000

DOSE

  • IV: titrated to APTT (usually: 80 U/kg bolus then 18 U kg/h and check APTT at 6h – aiming for 60-80 seconds)
  • SC: 5000 12hrly or q8h in the obese for VTE prophylaxis

INDICATIONS

  1. prevention of venous thromboembolism
  2. priming of cardiopulmonary bypass or haemodialysis
  3. maintenance of patency of indwelling lines
  4. DIC
  5. fat embolism

ADVERSE EFFECTS

  • bleeding
  • thrombocytopaenia (HITS type 1 and 2)
  • osteoporosis

PHARMACOKINETICS

  • Absorption – SC or IV
  • Distribution -1/3 bound to antithrombin III, 2/3 bound to albumin, fibrinogen & proteases, Vd = 40-100 mL/kg
  • Metabolism – liver, renal and reticuloendothelial system
    Elimination – urine, t ½ = 2 hrs

OTHER INFORMATION

Activity can be tested by:

1. APTT
2. Anti-Xa assay
3. Activated Clotting Time [ACT]

Reasons for failure of heparin anticoagulation:

  • insufficient dose (e.g. dose error, increased protein binding, increased clearance)
  • failure can occur with infections, fever, cancer, post-operative state or other thrombophilia
  • antithrombin III deficiency
  • high Factor VIII
  • DIC
  • high clot burden

How to correct failure to anticoagulate with heparin:

  • confirm correct dose/ rate
  • consider changing to LMWH
  • consider antithrombin III concentrate (or FFP or cryoprecipitate)

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health, a Clinical Adjunct Associate Professor at Monash University, and the Chair of the Australian and New Zealand Intensive Care Society (ANZICS) Education Committee. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.