Low-molecular-weight heparins (LMWH)

[SH4:p511]

Examples of LMWH include:

• Enoxaparin
• Dalteparin

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