Abstract

The direct thrombin inhibitor melagatran (Exanta™, Astra Zeneca, Sweden) has proven efficient for the prevention and treatment of thromboembolism. Major bleeding complications are rare and may often be managed by discontinuation of the drug; however, in some cases of acute serious bleeding, an effective and instant haemostatic intervention may be needed. Potential haemostatic agents may include recombinant factor VIIa (rFVIIa - NovoSeven®, Novo Nordisk, Denmark) or activated prothrombin complex concentrate (APCC - Feiba®, Baxter, Austria). We hypothesized that melagatran induces abnormal whole blood (WB) clotting profiles and rFVIIa as well as APCC may improve the deteriorated clotting profiles. This study aimed to investigate the effect of ex vivo addition of melagatran to WB from healthy males and explore the haemostatic potential of rFVIIa and APCC. Following informed consent, 15 healthy males with an average age of 34 years were enrolled for blood sampling. Continuous WB coagulation profiles were recorded by ROTEG® thrombelastography employing activation with minute amounts of tissue factor (Innovin® final dilution 1:17,000 ~0.35pM). The initiation phase of WB clot formation was defined by the clotting time (CT - sec). Coagulation raw data were processed to provide dynamic parameters that concur with the propagation of WB coagulation such as maximum velocity (MaxVel - mm*100/sec) and time to maximum velocity (t, MaxVel - sec). Titration experiments (n=10) with ex vivo addition of melagatran to WB corresponding plasma concentrations ranging from 0 to 5.0 μM (12 steps) showed a significant and dose dependent prolongation of the CT and t, MaxVel. The MaxVel of WB clot formation was initially reduced from average 13.8 mm*100/sec (12.2-15.4, 95 % CI) to a plateau level of average 9.6 (7.5–12.2) at concentrations of melagatran ranging from 0.125 μM to 0.50 μM. A further and progressive decline in MaxVel was observed at concentrations of melagatran exceeding 1.0μM. Intervention studies (n=10) were performed ex vivo on WB spiked with melagatran at 0.25, 0.50, 1.0, and 2.0 μM followed by ex vivo addition of rFVIIa at concentrations of 25, 50, 100, and 200 nM or APCC at concentration of 0.5, 1.0, 2.0, and 4.0 U/mL. In all tested concentrations of melagatran, rFVIIa significantly shortened the CT and t, MaxVel, while the reduced MaxVel was not accelerated. No dose-response effect of rFVIIa was detected. In contrast, at all concentration of melagatran, APCC significantly and dose dependently shortened the CT, the t, MaxVel as well as increased the MaxVel. As compared to rFVIIa, the effect of APCC was statistically more potent. At melagatran 0.25 μM, APCC at 1.0, 2.0, and 4.0 U/mL normalized the MaxVel. In all other experimental settings, rFVIIa or APCC did not normalize the dynamic WB coagulation parameters following anticoagulation with melagatran. In conclusion, melagatran induces unique changes of dynamic WB clot formation as illustrated by the prolonged initiation and plateau interval of MaxVel in clot propagation. rFVIIa as well as APCC significantly improved the WB clot formation, although reversal of melagatran anticoagulation was not obtained. The more pronounced effect of APCC may be caused by addition of prothrombin and activated coagulation factors. However, this intervention may be less safe than use of rFVIIa.

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