Effects of ZK-807834, a novel inhibitor of factor Xa, on arterial and venous thrombosis in rabbits

Inhibition of factor Xa (FXa) may interrupt thrombus progression. This study compared the antithrombotic activity of a novel FXa inhibitor, ZK- 807834 [MW, 527 D; K(i) (human FXa), 0.11 nM], with recombinant tick anticoagulant peptide [rTAP; MW, 6,685 D; K(i), (human FXa) = 0.28 nM], and DX-9065a [MW 445 D, K(i) (human FXa), 40 nM] in rabbits with arterial thrombosis induced by electrical vascular injury. ZK-807834 also was compared with low molecular weight heparin (LMWH; MW, 5,500 D) during venous thrombosis induced by placing a copper wire and threads in the vena cava. Inhibitors were administered as an i.v. bolus and 2-h infusion. Total dosages of ZK-807834, ≥0.7 μmol/kg (n = 18); rTAP, ≥1 μmol/kg (n = 18); or DX- 9065a, ≥11 μmol/kg (n = 18) decreased the incidence of arterial thrombotic occlusion compared with control animals (p < 0.05). However, five of six animals given the lowest effective dosage of rTAP and four of six animals given DX-9065a bled from a surgical incision >5 min, but only two of six animals given ZK-807834 bled >5 min. Venous clot weights were reduced compared with controls for dosages of ZK-807834 ≥0.007 μmol/kg (n = 36) or LMWH ≥0.2 μmol/kg (n = 18). Prothrombin time (PT) and activated partial thromboplastin time (aPTT) were unchanged from baseline at the minimally effective dose of ZK-807834, whereas aPTT was increased twofold at the effective dose of LMWH. Thus ZK-807834 may be useful to attenuate thrombosis at lower dosages and with less perturbation of system c hemostasis compared with available agents.