heparin

Question 1

types of heparin + moa

Answer 1

There are two main types of heparin -

1. unfractionated, ‘standard’ heparin or
2. low molecular weight heparin (LMWH).

Heparins generally act by activating antithrombin III.

Unfractionated heparin forms a complex which inhibits thrombin, factors Xa, IXa, XIa and XIIa

LMWH however only increases the action of antithrombin III on factor Xa

Question 2

differences between standard heparin + LMWH

Answer 2

Question 3

what is HIT

Answer 3

Heparin-induced thrombocytopaenia (HIT)

• immune mediated - antibodies form against complexes of platelet factor 4 (PF4) and heparin
• these antibodies bind to the PF4-heparin complexes on the platelet surface and induce platelet activation by cross-linking FcγIIA receptors
• usually does not develop until after 5-10 days of treatment
• despite being associated with low platelets HIT is actually a prothrombotic condition
• features include a greater than 50% reduction in platelets, thrombosis and skin allergy
• treatment options include alternative anticoagulants such as lepirudin and danaparoid

Question 5

what metabolic disturbance can both types cause?

Answer 5

Both unfractionated and low-molecular weight heparin can cause hyperkalaemia. This is thought to be caused by inhibition of aldosterone secretion.

Question 6

how to revrese effects of heparin

Answer 6

Heparin overdose may be reversed by protamine sulphate, although this only partially reverses the effect of LMWH.