Thursday, 7 October 2010

MRCP revision battle 26.6: Heparin

Heparin comes in 2 'flavours':
  1. low molecular weight heparin (AKA dalteparin/fragmin, enoxaparin/clexane, tinzaparin) 
  2. unfractionated (AKA 'heparin')

So what are the differences?
  • molecular weight
    • LMW heparin, as the name suggests, has a lower molecular weight - 5000 compared to unfractionated heparin's 13000
  •  half life
    • LMW heparin has a longer half life than unfractionated heparin
  •  mechanism of action
    • LMW heparin inhibits factor Xa but has little effect on antithrombin
    • unfractionated heparin binds antithrombin
  • affect on aPTT
    • LMW heparin has little effect on aPTT
    • unfractionated heparin prolongs aPTT
  • side effects
    • both can cause osteoporosis and thrombocytopenia but the risks are greatest with unfractionated heparin
  • reversibility
    • unfractionated heparin can be fully reversed by protamine
    • LMW heparin cannot be fully reversed by protamine

A side effect of protamine to be aware of is hypotension.

HIT (=heparin induced thrombocytopenia) is a potentially serious side effect of heparin use which will be covered tomorrow.

With that to look forward to lets shake on to the last battle of the day, essential tremor...