A low molecular weight heparin compared with unfractionated heparin

Area of Science:

• Pharmacology and Toxicology
• Biochemistry and Molecular Biology

Background:

• Low molecular weight heparin (LMWH) is a derivative of unfractionated heparin with potential therapeutic advantages.
• Standard in vitro clotting assays are commonly used to assess heparin activity but may not fully reflect in vivo efficacy and safety.

Purpose of the Study:

• To compare the in vitro and in vivo activity of a 6000 dalton LMWH with unfractionated heparin.
• To evaluate the predictive value of standard clotting assays for the in vivo behavior of LMWH.

Main Methods:

• In vitro and in vivo comparative study of LMWH and unfractionated heparin.
• Assays included standard clotting tests (APTT, calcium thrombin time) and anti-Factor Xa activity.
• Subcutaneous injection was used for in vivo administration.

Main Results:

• The LMWH exhibited high and sustained in vivo activity by anti-Factor Xa assays post-subcutaneous injection.
• In vitro clotting assays showed unimpressive results for LMWH, with APTT and calcium thrombin time similar to unfractionated heparin.
• Clotting assays did not suggest a lower incidence of hemorrhagic side effects for this LMWH.

Conclusions:

• Standard in vitro clotting assays are inadequate for assessing the in vivo behavior and potential side effects of LMWH.
• Anti-Factor Xa assays provide a more relevant measure of in vivo LMWH activity.
• Further research is needed to establish appropriate assays for predicting LMWH clinical efficacy and safety.