Recombinant Human FVIIa Reduces Heparin and Low Molecular Weight Heparin (LMWH)-Induced Bleeding in Rats. (2005)

Abstract Recombinant human FVIIa (rFVIIa, NovoSeven, Novo Nordisk A/S) is approved for treatment of bleeding in hemophilia patients with inhibitors. Recent data indicate that rFVIIa is useful in other bleeding conditions. Heparin and low molecular weight heparin (LMWH) are widely used for anticoagulant management of venous thromboembolic events. Both agents can however cause uncontrollable bleeding. While protamine can reverse the anticoagulant effect of heparin no effective antidote for LMWH is currently available. We have tested if rFVIIa was capable of reducing the bleeding caused by either heparin or LMWH in a rat tail bleeding model. We pre-treated rats with a single dose of either heparin (Heparin, Leo; 200 IU/kg; i.v.) or LMWH (tinzaparin; Innohep, Leo; 500 IU/kg; i.v.), which significantly prolonged total bleeding time following tail transection (table 1). Similarly, blood loss increased significantly by pre-treatment with heparin and tinzaparin (table 2). rFVIIa, intravenously injected 5 minutes after induction of tail bleeding in doses of 5, 10 and 20 mg/kg (n=8), dose-dependently reduced bleeding time of the heparin-induced bleeding, reaching statistical significance at 20 mg/kg (table 1). In accordance, blood loss decreased significantly by treatment with 10 and 20 mg/kg rFVIIa (table 2). A similar response was seen in the tinzaparin pre-treated animals with a dose-dependent decrease in bleeding time (table 1), and a significant decrease in blood loss at 10 and 20 mg/kg rFVIIa (table 2). Table 1. Total bleeding time (s) Group Heparin 200 IU/kg (n=8)# Tinzaparin 500 IU/kg (n=9)# Data are analyzed using Mann-Whitneys U-test (A-B) or Kruskall-Wallis test with Dunn’s post-test (B-E). Asterisks indicate statistical significance at: *: p<0.05; **: p<0.01 and ***: p<0.001. #observation period 1800 s. A: No anticoagulant 293 ± 68 542 ± 180 B: Anticoag.+Vehicle 1668 ± 83 ***vs. A 1800 ± 0 ***vs. A C: Anticoag.+5 mg/kg rFVIIa 1194 ± 182 1732 ± 45 D: Anticoag.+10 mg/kg rFVIIa 1023 ± 230 1483 ± 152 E: Anticoag.+20 mg/kg rFVIIa 448 ± 66 **vs. B 1038 ± 206 *vs. B Table 2. Blood loss (nmol hemoglobin/ml) Group Heparin 200 IU/kg (n=8)# Tinzaparin 500 IU/kg (n=9)# Data are mean ± SEM. Data are analyzed after log transformation using Student’s t-test (A-B) or one-way ANOVA with Bonferroni’s post-test (B-E). Asterisks indicate statistical significance at: *: p<0.05; **: p<0.01 and ***: p<0.001. #observation period 1800 s. A: No anticoagulant 4.2 ± 4.0 4.9 ± 4.9 B: Anticoag.+Vehicle 53 ± 19 **vs. A 151 ± 37 ***vs. A C: Anticoag.+5 mg/kg rFVIIa 10.6 ± 5.6 32.3 ± 10.3 D: Anticoag.+10 mg/kg rFVIIa 0.73 ± 0.34 **vs. B 7.7 ± 2.8 ***vs. B E: Anticoag.+20 mg/kg rFVIIa 4.0 ± 1.9 *vs. B 22.6 ± 9.4 *vs. B This study illustrates the pharmacological effect of rFVIIa in the presence of heparin and LMWH and the results indicate that rFVIIa may be an effective way to treat heparin and LMWH induced bleeding, however the dose requirements are specific for the rat and cannot be extrapolated to other species. Future studies will investigate the hemostatic effect of rFVIIa in bleedings induced by coumarin analogues, thrombin inhibitors, factor Xa inhibitors, and platelet inhibitors.