Low-molecular-weight heparins (LMWH)
[SH4:p511]
Examples of LMWH include:
Structure
- Derived from standard commercial-grade unfractionated heparin by chemical depolymerisation
- Approximately 1/3 of heparin in size
- MW = 4000 to 5000 daltons
Pharmacodynamics
Comparison with heparin
- Greater inhibitory effect on activated factor 10
* Anti-10a : Anti-2a = 2:1 ~ 4:1
* c.f. For heparin --> 1:1
- Lower protein-binding
--> Better bioavailability at low doses
--> More predictable response
- Better in DVT prophylaxis in high-risk patients
- Less binding to endothelial cells
--> Longer elimination half-time (4 - 5 hours)
- Therapeutic doses usually do not affect the prothrombin time and APTT
- Protamine neutralise about 65% of anti-10a activity of LMWH
Trivia
[SH4:p511]
- Pentasaccharide consists of very low MW heparin
* Elimination half-time = ~ 24 hours