Introduction
There are two main types of heparin - unfractionated, 'standard' heparin or low molecular weight heparin (LMWH).
Mechanism of action
Heparins generally act by activating antithrombin III. Unfractionated heparin forms a complex which inhibits thrombin, factors Xa, IXa, XIa and XIIa.
Adverse effects
Adverse effects of heparins include:
- bleeding
- thrombocytopenia - see below
- osteoporosis and an increased risk of fractures
- hyperkalaemia - this is thought to be caused by inhibition of aldosterone secretion
Monitoring
The anticoagulant effect of heparin is monitored by the activated partial thromboplastin time (APTT)