Antithrombotic and Bleeding Effects of a New Synthetic Direct Thrombin Inhibitor and of Standard Heparin in the Rabbit

Abstract

SummaryThis study reports on (he anticoagulant, antithrombotic and bleeding effects of a new synthetic direct thrombin inhibitor (SDTI) in comparison with standard heparin (SH). The anticoagulant effect was determined with the thrombin clotting time (TCI) and the activated partial thromboplastin time (APTT). SDTI was more potent than SII in prolonging the TCT, but as potent as SH in prolonging the APTT. The antithrombotic effect was determined using a modified Wessler model in the rabbit, either 30 min after a continuous IV infusion of increasing doses or at various times after a single SC injection (20 mg/kg). After continuous IV infusion of 187 μg/kg/h of SDTI and of 60 μg/kg/h of SH, significant thrombus prevention effects were obtained (59 and 57% respectively). Increasing the dose of SDTI up to 3000 μg/kg/h did not significantly impiove the antithrombotic effect. After SC injection, a significant antihrombotic effect was observed for 12 h with SDTI but for more than 24 h with SH. The bleeding effect was studied using the rabbit ear model 15 min after a continuous infusion of 7.5 and 15 mg/kg/h: the amounts of blood loss were dose-dependent and comparable for SDTI and SH. These studies also indicated that SDTI possesses a considerable shorter half-life in comparison with SH. Accordingly, the ex vivoconcentrations generated after continuous IV infusion or SC injection of the same dose were higher for SH than for the SDTI.