Dabigatran Neutralizing Antobody, Idarucizumab, Exhibits Procoagulant and Platelet Activation Responses in Whole Blood. Potential Clinical Implications

Introduction: Idarucizumab is a humanized monoclonal antibody fragment which is capable of neutralizing Dabigatran and is currently clinically available for the control of bleeding associated with Dabigatran. Although this antibody is capable of neutralizing the anticoagulant effects of Dabigatran, its effect on the blood coagulation and platelet activation profile are not completely understood. There is limited data on the effect of Idarucizumab on the blood coagulation and platelet activation profile. The purpose of this study is to determine the effect of this antibody on blood coagulation and platelet activation profile.

Materials: Idarucizumab was purchased from Brigham and Women's Hospital (Boston, MA) and was provided as a 50 mg/mL solution. Dabigatran was of synthetic origin and obtained from Sellec Chemical (Houston, TX). Whole blood from healthy volunteers was collected in plastic syringes using a sterile method for the TEG and ACT analysis. Citrated whole blood was used for the preparation of platelet rich plasma which was used in platelet aggregation studies. Such agonists as arachidonic acid, ADP, epinephrine, thrombin, and collagen were used.

Methods: The TEG studies were carried on a Haemoscope 500 instrument. Native whole blood was supplemented with Idarucizumab in a concentration range of 0-10 mg/mL. Saline was used as a control. The TEG profile was measured for 15-30 minutes. Such parameters as R time, K time, angle, and max amplitude were recorded. The ACT studies were carried out in celite tubes in a concentration of 0-5 mg/mL. The agonist-induced platelet aggregation profile was studied by pre incubating platelet rich plasma with Idarucizumab at a fixed concentration of 1.0 mg/mL and studying its effect on the aggregation profile of such agonists as arachidonic acid, ADP, epinephrine, thrombin, and collagen. Both the slope and percent aggregation were measured. The effect of Idarucizumab on HIT antibodies mediated platelet aggregation was studied by pre incubating platelets with Idarucizumab and determining its effect on the HIT antibody mediated aggregation of platelets. Pooled plasma from symptomatic HIT patients was pre incubated with Idarucizumab at 1.0 mg/mL followed by the addition of HIT antibody pool in a 1:10 dilution. The aggregation profile was noted for up to an hour.

Results: Idarucizumab produced a dose-dependent hypercoagulable effect in the TEG profile of native whole blood resulting in a reduction in R time and max amplitude at 35% and 45% respectively. At high concentrations, Idarucizumab produced a marked effect on the clot retraction. In the ACT studies, Idarucizumab produced a mild shortening of the ACT at a 5 mg/mL at 6%. Idarucizumab produced variable augmentation of different agonists mediated platelet aggregation. In the HIT mediated aggregation studies, Idarucizumab produced a strong augmentation of HIT antibody mediated platelet aggregation. At 1.0 ug/mL, Idarucizumab produced almost a 20% increase in platelet aggregation.

Conclusions: These studies indicate that Idarucizumab produces mild procoagulant effects on whole blood coagulation process as studied by TEG and ACT. This agent also produces the augmentation of the platelet aggregation profile by various agonists including Anti-heparin platelet factor IV antibodies. These procoagulant effects of Idarucizumab may contribute to the potential hypercoagulable/prothrombotic events associated with its use.