Estimation of dabigatran plasma concentrations in the perioperative setting

SummaryThe perioperative management of dabigatran is challenging, and recommendations based on activated partial thromboplastin time (aPTT) and thrombin time (TT) are unsatisfactory. Dedicated coagulation tests have limitations at plasma concentrations < 50 ng/ml. Therefore, a more sensitive test, which is available 24/7, is required. It was the aim of this study to investigate the performance of the Hemoclot Thrombin Inhibitors® LOW (HTI LOW) kit, a diluted thrombin time, and the STA® – ECA II (ECA-II) kit, a chromogenic variant of the ecarin clotting time, that were developed to measure low dabigatran concentrations, compared to reference dabigatran analysis by liquid chromatography tandem mass-spectrometry (LC-MS/MS). This study included 33 plasma samples from patients treated with dabigatran etexilate who had plasma concentrations < 200 ng/ml. HTI LOW and ECA-II were performed along with HTI, aPTT (STA®-C. K.Prest® and SynthasIL ®) and TT (STA® – Thrombin). All procedures were performed according to recommendations by the manufacturers. Linear (or curvilinear) correlations and Bland-Altman analyses were calculated. For free dabigatran concentrations < 50 ng/ml, the R2 of linear correlations were 0.69, 0.84 and 0.61, with HTI, HTI LOW and ECA-II, respectively. The R2 for TT, STA®-C. K.Prest® and SynthasIL® were 0.67, 0.42 and 0.15. For HTI, HTI LOW and ECA-II, Bland-Altman analyses revealed mean differences of –6 ng/ml (95 %CI: –25–14 ng/ml), 1 ng/ml (95 %CI: –18–19 ng/ml) and –1 ng/ml (95 %CI: –25–23 ng/ml), demonstrating that tests dedicated to measuring low concentrations are more accurate than HTI. In conclusion, the use of HTI LOW or ECA-II to assess low plasma dabigatran concentrations is supported by our findings.

Abstract 18403: Effect of Dabigatran on the Ability to Generate Fibrin at a Wound site and its Reversal by Idarucizumab, the Antidote to Dabigatran, in Healthy Volunteers: An Exploratory Marker of Blood Loss

Background: Idarucizumab is a humanized antibody fragment (Fab) that specifically and potently binds dabigatran to neutralize its anticoagulant activity. Assessing whether reversal of anticoagulation also reverses bleeding is challenging. This healthy volunteer (HV) study explored dabigatran’s ability to inhibit fibrin formation in blood at a non-penetrating wound site by measuring fibrinopeptide A (FPA) generation and to test whether idarucizumab restores wound site fibrin formation. Methods: The study followed the Declaration of Helsinki with HV written informed consent. Dabigatran etexilate (DE, 220 mg bid) was given for 4 days. FPA was assessed before DE and on day 3 and 4 at 2.5 and 6 hrs post morning DE dose. On day 4, HV received 5 min infusion of 1, 2 or 4 g of Fab or placebo 2 hrs post morning DE dose (n=8-9/group). Incisions were made with a scalpel device (Surgicutt®) on the forearm volar surface. Blood was collected from the wound at each time point over 4 min into vials containing stop solution and frozen until assayed. FPA was measured via commercial ELISA, ecarin clotting time (ECT) and diluted thrombin time (dTT) using standard methods. Plasma dabigatran levels were measured by LC-MS/MS. Data expressed as mean ± SE and analyzed using two way ANOVA, p<0.05 as significant. Results: Fab and dabigatran were well tolerated. Mean FPA before DE was 3980 ± 1735 ng/ml (n=35). There was almost complete inhibition of FPA to 208 ± 28 ng/mL 2.5 hrs post DE day 3, corresponding to peak dabigatran levels (210 ± 17 ng/mL). Six hrs post DE, levels were 127 ± 10 ng/mL and FPA was still significantly reduced to 328 ± 35 ng/mL (pooled day 3 data). There was a significant, dose-dependent return of fibrin formation with increasing doses of Fab to 24, 45 and 63% of pre DE values 30 min after 1, 2 and 4 g Fab, respectively (p<0.05). Anticoagulation (ECT and dTT) was significantly prolonged with dabigatran and reversed to control levels after dosing with 2 and 4 g Fab. Discussion: This study demonstrates that idarucizumab reverses dabigatran-induced inhibition of wound site fibrin formation in HV and this correlated with reversal of systemic anticoagulation. Translation into reversal of bleeding in patients requires further clinical investigations, which are currently ongoing.

Impact of dabigatran on a large panel of routine or specific coagulation assays

SummaryDue to low bioavailability and high inter-individual variability, monitoring of dabigatran may be required in specific situations to prevent the risk of bleedings or thrombosis. The aim of the study was to determine which coagulation assay(s) could be used to assess the impact of dabig-atran on secondary haemostasis. Dabigatran was spiked at concentrations ranging from 4.7 ng/ml to 943.0 ng/ml in pooled citrated human platelet-poor plasma. The following clotting assays were performed: prothrombin time (PT); activated partial thromboplastin time (aPTT); thrombin time (TT); ecarin clotting time (ECT); ecarin chromo-genic assay (ECA); prothrombinase-induced clotting time (PiCT); activated clotting time (ACT); Hemoclot Thrombin Inhibitor (HTI) and thrombin generation assay (TGA). A concentration-dependent prolongation of PT, dPT, and aPTT was observed with aPTT being the more sensitive test. The results varied mostly due to the clotting reagent. HTI, ECT and TGA were the most sensitive tests but are not available 24 hours a day. In addition, HTI showed a linear correlation with a good reproduci-bility. Dabigatran induced a concentration-dependent delay and inhibition of tissue factor-induced TGA. Cut-offs related with higher risk of bleedings or thrombosis were defined for each reagent of aPTT and HTI. In conclusion, aPTT could be used for the monitoring of dabigatran and as screening test for the risk of overdose. However, because of its higher sensitivity, good reproducibility, excellent linear correlation at all doses, its simplicity of use, and possibilities of automation, HTI should be considered as the gold-standard.