Characterisation of antithrombin-dependent anticoagulants through clot waveform analysis to potentially distinguish them from antithrombin-independent inhibitors targeting activated coagulation factors

Aims While antithrombin (AT)-independent inhibitors targeting thrombin or activated factor X have been assessed through clot waveform (CWA), there are no reports on assessment with respect to AT-dependent anticoagulants. The present study aims to characterise AT-dependent anticoagulants through CWA to distinguish them from AT-independent inhibitors. Methods CWA was applied to the activated partial thromboplastin time (APTT) assay of plasma samples spiked with each of AT-dependent drugs (unfractionated heparin, enoxaparin and fondaparinux) and AT-independent drugs (rivaroxaban, apixaban, edoxaban, dabigatran, argatroban, hirudin and bivalirudin), which was performed using the CS-5100 or CN-6000 (Sysmex). The APTT-CWA data were automatically gained by the analyser program. The positive mode of clotting reaction curves was defined as the direction towards fibrin generation. Results Regarding dose-response curves in AT-dependent anticoagulants, the maximum positive values of the first and secondary derivatives (Max1 and Max p 2, respectively) and the maximum negative values of the secondary derivative (Max n 2) seemed to drop to zero without making an asymptotic line, consistent with the irreversibility. Such a feature was observed also in hirudin, as reported previously. Notably, the symmetric property of Max1 peaks in the waveforms was distorted dose dependently in AT independent but not AT-dependent drugs. A plot of Max p 2 logarithm versus Max n 2 logarithm was linear. The slope was about 1 in AT-dependent drugs while that was more than 1 in AT-independent drugs. These features made it possible to distinguish AT-dependent and AT-independent drugs. Conclusions The results aid in further understanding of the pharmacological aspects of anticoagulation and in screening of candidates for novel anticoagulants.