In Vitro Evaluation of the Effect of rFVIIa on Anti Coagulated Human Whole Blood Treated with Abciximab Using Thromboelastography (TEG).

Abciximab inhibits platelet aggregation by binding to GPIIb/IIIa. Thus, Abciximab is effective in prevention and treatment of thromboembolic events. Although major bleeding complications are rare, Abciximab has the potential to increase bleeding which often is managed by temporary discontinuation of administration of drug. However, an effective and instant haemostatic intervention may be needed in some cases of acute serious bleeding. The aim of this study was to investigate 1) the effect of in vitro addition of Abciximab to whole blood (WB) from 8 healthy donors, 2) to determine the haemostatic potential of ex vivo addition of 10, 25 (25nM^≈90ug/kg), and 100nM rFVIIa (NovoSeven^®, Novo Nordisk) to WB treated with 4μg/ml of Abciximab (ReoPro^®, Lilly) and 3) to compare the response of rFVIIa in TEG assays containing tissue factor (TF, Innovin 1:42500) or Kaolin (standard initiator provided by Haemsoscope) with or without tPA (0.75nM). TEG Platelet Mapping was performed on all Abciximab-treated blood samples before conducting TEG demonstrating 70–100% inhibition of ADP-induced platelet aggregation. The following TEG parameters were used: Reaction time (R-time), Maximum Thrombin generation (MTG), Maximum Amplitude (MA) and Area under the TEG fibrinolysis curve calculated from MA (AUC lysis). The statistical analysis was performed by a two-way ANOVA model. A significant effect of adding rFVIIa (10 nM) to Abciximab-treated blood was observed for all clot formation parameters and with both TF and Kaolin as initiator. rFVIIa demonstrated a significant dose-dependent improvement of the TEG parameters in the assay containing kaolin, in kaolin+tPA (except MA) and in TF (except for MTG). rFVIIa showed significant dose-dependent protection against clot lysis (AUC lysis) in the assay containing kaolin+tPA, whereas no significant effect on clot lysis was observed in the assay containing TF. In conclusion, addition of rFVIIa to WB treated with Abciximab significantly improves most of the TEG parameters. Comparison of Abciximab+rFVIIa TEG parameters with TEG parameters obtained in normal WB (n=59) showed normalization of the R-value, however, none of the other TEG parameters reached normal values although a significant effect was observed after addition of rFVIIa. The TEG assay using kaolin as initiator showed significant dose-dependent effect of rFVIIa on all TEG parameters. In contrast, in the TEG assay initiated with TF the dose-dependent response of rFVIIa was only significant for some of the parameters. This may be due to a strong initiating effect of TF in the assay thus lowering the sensibility to rFVIIa. In contrast, in the assay initiated with Kaolin only TF-independent effects of rFVIIa are measured. The design of a TEG assay therefore seems to be important for evaluating the in vitro effect of rFVIIa. The clinical relevance of these findings is currently unknown and needs to be evaluated further.