Influence of bivalirudin on tissue factor-triggered coagulation

Continuous thrombin generation in whole blood: New applications for assessing activators and inhibitors of coagulation

Hemostatic tests have been utilized to clarify the blood coagulation potential. The novel thrombin generation (TG) assay of this study provides explicit information and is the most physiologically-relevant hemostatic test ex vivo. We describe how this assay allows for TG under a number of relevant circumstances. First, whole blood (WB) from healthy individuals was analyzed ± 5 pM tissue factor (TF) and ± contact pathway inhibition. Without an exogenous initiator TG was decreased and delayed, but addition of 5 pM TF shortened the lag phase and increased peak thrombin. Additional experiments included fresh WB from a trauma patient analyzed for endogenous activity and TG from healthy donors subjected to TG antagonists which prolonged the lag phase whereas TG agonists consistently shortened the lag phase in a dose dependent manner. Lastly, platelet-poor plasma was reconstituted with packed red blood cells and TG was monitored in the presence and absence of both TF as an activator and PCPS as a phospholipid surface. Our data illustrate the potential that this continuous TG assay has in the evaluation of disorders relevant to blood coagulation and in the monitoring of treatments administered in response to these disorders.

Thrombalexin: Use of a Cytotopic Anticoagulant to Reduce Thrombotic Microangiopathy in a Highly Sensitized Model of Kidney Transplantation

Early activation of coagulation is an important factor in the initiation of innate immunity, as characterized by thrombotic microangiopathy (TMA). In transplantation, systemic anticoagulation is difficult due to bleeding. A novel "cytotopic" agent, thrombalexin (TLN), combines a cell-membrane-bound (myristoyl tail) anti-thrombin (hirudin-like peptide [HLL]), which can be perfused directly to the donor organ or cells. Thromboelastography was used to measure time to clot formation (r-time) in both rhesus and human blood, comparing TLN versus HLL (without cytotopic tail) versus negative control. Both TLN- and HLL-treated rhesus or human whole blood result in significantly prolonged r-time compared to kaolin controls. Only TLN-treated human endothelial cells and neonatal porcine islets prolonged time to clot formation. Detection of membrane-bound TLN was confirmed by immunohistochemistry and fluorescence activated cell sorter. In vivo, perfusion of a nonhuman primate kidney TLN-supplemented preservation solution in a sensitized model of transplantation demonstrated no evidence of TLN systemically. Histologically, TLN was shown to be present up to 4 days after transplantation. There was no platelet deposition, and TMA severity, as well as microvascular injury scores (glomerulitis + peritubular capillaritis), were less in the TLN-treated animals. Despite promising evidence of localized efficacy, no survival benefit was demonstrated.

Bivalirudin as a bridge for anticoagulation in high risk neurosurgical patients with active DVT or high risk of thrombosis

BACKGROUND

Bivalirudin is an ultrashort acting direct thrombin inhibitor, which has been used in place of heparin in selected settings. We describe our preliminary experience with the use of bivalirudin in patients who required anticoagulation for a deep vein thrombosis, prosthetic heart valve, or hypercoagulable state but were felt to be at high risk for the use of heparin.

METHODS

Eight patients in our neurocritical care unit required anticoagulation but were felt to be poor candidates for heparin either due to heparin-induced thrombocytopenia or due to high risk for intracranial hemorrhage. A standard protocol was utilized for bivalirudin with a loading dose of 0.75 mg/kg followed by a continuous infusion of 0.15 mg/kg hr. Serial aPTT levels were checked on a routine basis to monitor therapeutic effect. The bivalirudin infusion was continued for a period of 2 days to 2 weeks prior to starting coumadin therapy.

RESULTS

These patients were in the early postoperative period (within 48 h) following craniotomy, had suffered a recent large hemispheric infarct with hemorrhagic conversion, or had presented with an acute intracerebral hemorrhage. In this small series of patients, no intracranial hemorrhagic complications were encountered. No patients demonstrated progressive systemic thrombotic issues while on bivalirudin.

CONCLUSION

Based on these findings, bivalirudin may represent a reasonable alternative in patients for whom heparin anticoagulation is contraindicated. A larger multicenter trial of bivalirudin in this setting may be appropriate.

Bivalirudin is inferior to heparin in preservation of intraoperative autologous blood

INTRODUCTION

Bivalirudin is used as an alternative to heparin in cardiac surgery, and may be superior to heparin with regard to platelet function. Bivalirudin however, is prone to cleavage by thrombin resulting in coagulation in areas of stasis.

MATERIAL AND METHODS

We compared the preservation of platelet function and the quality of anticoagulation in autologous blood of 26 cardiac surgical patients collected intraoperatively and anticoagulated ex vivo with either bivalirudin or heparin, with supplementation of bivalirudin over time and prevention of stasis.

RESULTS

We found in both preservatives a reduction in ADP-induced platelet aggregation response over a period of 105 minutes (median, IQR: 73-141) as measured by Multiplate®. Supplementation of additional bivalirudin (23 ± 1.1 μg/ml/hr) and prevention of stasis was not able to prevent thrombin generation. We found a 5-fold increase in levels of prothrombin fragment 1+2 in bivalirudin preserved autologous blood as compared to heparin preserved blood (F(1+2) levels median 8.9 nM [quartile percentiles 4.2-12.4] vs 1.3 nM [0.6-2.1], P=0.001 Mann-Whitney, n=10).

CONCLUSIONS

Our study suggests that preservation of platelet function in autologous blood anticoagulated with bivalirudin is not a suitable alternative to heparin.

Empirical and theoretical phenotypic discrimination

We have developed an integrated approach that combines empirical and computational methodologies to define an individual's thrombin phenotype. We have evaluated the process of thrombin generation in healthy individuals and individuals with defined pathologies in order to develop general criteria relevant to assess an individual's propensity for hemorrhage or thrombosis. Three complementary hypotheses have emerged from our work: (i) compensation by the ensemble of other coagulation proteins in individuals with specific factor deficiencies can 'normalize' an individual's thrombin generation process and represents a rationale for their unexpected phenotype; (ii) individuals with clinically unremarkable factor levels may present thrombin generation profiles typical of individuals with hemostatic complications; and (iii) in some hemostatic disorders a specific pattern of expression of a small ensemble of coagulation factors may be sufficient to explain the overall phenotype.

The Influence of Lepirudin, Bivalirudin and Dabigatran on the Calibrated Automated Thrombogram (CAT)

In a two centre study (laboratories in Diagnostica Stago and Biomnis) we compared the in vitro effect on thrombin generation (TG) of Dabigatran and Bivalirudin (reversible direct anti-IIa inhibitors) with that of Lepirudin (an irreversible direct anti-IIa inhibitor) spiked into normal pool plasma. The effect of Lepirudin, Bivalirudin and Dabigatran were evaluated in both centres using the CAT (Diagnostica Stago, France) TG method in a concentration ranges up to 5, 20 and 1 μg/mL respectively. Testing was done in triplicate and repeated over 2 days. To reduce assay variability both centres used the same reagents lots and the same normal pool plasma (George King, USA). The range of each drug tested extended well above the therapeutic range concentrations normally found in patient plasma (0.5 to 1.0 μg/mL, 5 to 10 μg/mL and 0.1 to 0.3 μg/mL respectively for Lepirudin, Bivalirudin and Dabigatran). To see the effect of increasing activation forces, TG was performed at 3 different final concentrations of Tissue Factor (TF) - 1, 5 and 20 pM. All reagents were used as recommended by the manufacturer (Thrombinoscope, The Netherlands). A prolongation in the lag time (LT) is observed with all 3 drugs with all 3 concentrations of TF, but this is more marked for Lepirudin and Bivalirudin than it is for Dabigatran. In the therapeutic range Dabigatran (at 5pM TF) shows both an increase in LT and a decrease in peak thrombin and the ETP. At low concentration of Bivalirudin or Lepirudin, there is a paradoxical increase in peak height, which is even more pronounced at low TF concentration. At 1pM TF, this paradoxical peak increase is also observed with Dabigatran.

Results obtained in both laboratories are similar and complement our previous results and those reported elsewhere (1–4). The effect of Lepirudin and Bivalirudin on TG is different from that of Dabigatran. We also note that at lower TF concentration the anticoagulant effect on TG initiation is more intense but the test becomes less reproducible.

Bivalirudin with provisional glycoprotein IIb/IIIa inhibitors in patients undergoing primary angioplasty in the setting of cardiogenic shock

In patients undergoing percutaneous coronary intervention (PCI), clinical trials have demonstrated that the use of bivalirudin with provisional glycoprotein IIb/IIIa inhibitors is not inferior to heparin with systematic glycoprotein IIb/IIIa inhibitors on major adverse cardiac events and is associated with lower rates of bleeding in various clinical settings. Patients with cardiogenic shock (CS), however, have been excluded from all pivotal trials. A retrospective analysis of 86 consecutive patients undergoing PCI for acute myocardial infarction complicated by CS in our center from April 2003 to September 2007 was performed. In-hospital death, major adverse cardiac events, and bleeding rates were compared in 37 patients who received bivalirudin with or without glycoprotein IIb/IIIa inhibitors and 49 patients who were treated with heparin and glycoprotein IIb/IIIa inhibitors as anticoagulation management. Baseline demographic, clinical, and biological characteristics were similar in the 2 groups. The in-hospital death rate was significantly lower in the bivalirudin group (5.4 vs 32.7%, p = 0.002). There were no differences in the rate of major hematoma between the bivalirudin group and the heparin group (3 vs 2.6%, p = 0.46). In conclusion, bivalirudin with provisional use of glycoprotein IIb/IIIa inhibitors appears to be a safe and effective anticoagualtion strategy in patients undergoing primary PCI for acute myocardial infarction complicated by CS.