A comparative study of recombinant hirudin and standard heparin in the Wessler model

The in vitro anticoagulant activity of recombinant desulphated hirudin (HBW 023) and its antithrombotic activity in a rabbit venous stasis model were assessed in comparison to unfractionated heparin (UH). The specific activity of r-hirudin in rabbit plasma is similar to that of unfractionated heparin on a weight basis when using the whole blood clotting time or APTT, while it was five times more potent according to the thrombin clotting time (TCT). Forty-eight (6x8) anaesthetized New Zealand male rabbits were randomized to receive HBW 023 (12.5, 25, 50, 100, 200, 400 micrograms.kg-1), standard heparin (90 micrograms.kg-1) or placebo. Five minutes after administration of the drug, the experimental thrombosis was induced by an injection of glass activated overnight human serum into the marginal vein of the ear and ligation of the jugular vein (Wessler model). The jugular vein was removed after 10 min stasis and examined by a researcher unaware of the treatment administered. In the Wessler stasis model the fresh thrombus weight and a score as well as the circulating level of r-hirudin using a chromogenic substrate assay were used to determine the inhibitory effect of the drug. Highly significant inverse correlations were found between fresh thrombus weight and the injected doses as well as r-hirudin plasma levels. The ID50 which was the dose of the drug that induced a complete inhibition of thrombosis in 50% of the dose group tests was about 200 micrograms.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)