Summary
The antithrombotic efficacy of unfractionated heparin (UFH), a low molecular weight
heparin (LMWH) and a synthetic pentasaccharide (PENTA) has been compared in an animal
model for stasis thrombosis. We have also compared the relative ability of these three
agents to impair thrombin generation in vitro and in vivo, and measured their effects
on anti-Xa activity and thrombin clotting times. UFH, LMWH and PENTA all had the capacity
to impair thrombogenesis, although there were marked differences in their relative
effectiveness. Reduction of thrombin generation to 20% of control values was closely
correlated with the prevention of thrombosis after 20 minutes’ stasis, but this was
only achieved with UFH. The same dry weight dose of LMWH or PENTA reduced thrombin
generation to about half control values, and neither significantly impaired thrombus
formation after 20 minutes’ stasis. Impaired thrombin generation correlated better
than anti-Xa activity with prevention of stasis thrombosis. In this model, UFH was
clearly superior to LMWH and PENTA as an antithrombotic agent.
Keywords
Heparin - Low molecular weight heparin - Pentasaccharide - Thrombosis - Thrombin generation
