Direct oral anticoagulants (DOACs) which include direct thrombin inhibitor dabigatran (Pradaxa®) have many clinical advantages over vitamin K antagonists, such as less interaction with drugs and food, a wider therapeutic window which enables a fixed dose regimen and requires no need for regular laboratory monitoring. The advantage of using dabigatran over vitamin K antagonists is the existence of specific reversal agent idarucizumab (Praxbind®) that binds dabigatran with higher affinity than thrombin, resulting in fast and complete neutralization of dabigatran anticoagulant activity.
In this study we included 44 patients with atrial fibrillation (AF) treated with dabigatran. Blood samples were collected from all patients before and during dabigatran treatment, to which we later added idarucizumab in vitro. We determined the effect of dabigatran and addition of idarucizumab in vitro using coagulation tests (PT, APTT and TT) and with thrombin generation assay (TGA). The results show that dabigatran increases APTT, lag time and time to peak thrombin with increasing concentrations of dabigatran as compared to samples before anticoagulant therapy. Dabigatran had no significant effect on thrombin peak. PT (%) and area under the curve were significantly lower than those before anticoagulant treatment because of the inhibiting activity of dabigatran. The in vitro addition of idarucizumab fully neutralizes anticoagulant activity of dabigatran, which we proved with normalization of PT, APTT, TT, lag time and time to peak thrombin, meanwhile thrombin peak and area under the curve remained elevated compared to samples before dabigatran treatment. In this study we showed that samples collected during anticoagulant treatment with dabigatran which inhibits thrombin prolonged APTT, lag time and time to peak thrombin, however, the in vitro addition of idarucizumab did not restore but rather significant shortened coagulation times compared to samples with no dabigatran. We got similar results in variables of thrombin generation assay, except in thrombin peak and area under the curve, which were significantly higher compared to samples before dabigatran treatment and did not reflect anticoagulant activity of dabigatran. Thrombin peak and area under the curve were not affected by the addition of idarucizumab in vitro, which we attribute to formation of complex (α2-macroglobulin-thrombin) during thrombin generation and contributes to the splitting of fluorescent substrate and consequently falsely increases results.