Dabigatran Levels Research Articles

Fully automated thromboelastograph TEG 6s to measure anticoagulant effects of direct oral anticoagulants in healthy male volunteers

BackgroundThe ability to assess the hemostatic effect of the direct oral anticoagulant (DOACs) may be valuable in clinical situations such as bleeding or thrombosis, before urgent surgery, or reversal of anticoagulation. We sought to assess the anticoagulant effect of DOACs with the new‐generation fully automated thrombelastograph TEG 6s using resonance‐frequency viscoelasticity measurements and disposable multichannel microfluidic cartridges. MethodsA single dose of oral dabigatran 150 mg, rivaroxaban 20 mg, or apixaban 5 mg was given to 9 healthy males. Phlebotomy was performed at 0, 1, and 3 hours after administration of DOAC. TEG parameters were measured using TEG_6s. Concentrations of DOACs were measured using chromogenic assays. The TEG parameters were correlated to the DOAC concentrations. ResultsThe reaction time (R) demonstrated the strongest response to DOAC intake. There were no correlations between other TEG parameters and DOAC concentrations. Using the direct thrombin inhibitor (DTI) channel, R was significantly correlated with dabigatran levels (r=0.94, P<0.0001). Using the anti–factor Xa (AFXa) channel, R was significantly correlated with rivaroxaban and apixaban levels (r=0.93 and r=0.83, respectively; P<0.0001 for both). R >2.5 minutes for dabigatran (DTI channel), >2.5 minutes for apixaban, and >1.8 minutes for rivaroxaban (AFXa channel) were associated with 100% sensitivity and ≥ 90% specificity to detect DOAC levels of ≥ 50 ng/mL. ConclusionWe have demonstrated that TEG_6s R has significant correlation with DOAC blood concentrations and has potential for monitoring the DOAC's effect on hemostasis with reasonable sensitivity in the small sample analyzed. This novel technology is easy to use on a small volume of whole blood without requiring a specialized laboratory. Further study is warranted to correlate R with clinical outcomes.

The Impact of Proton Pump Inhibition on Dabigatran Levels in Patients With Atrial Fibrillation.

Proton pump inhibition (PPI) administrated together with dabigatran reduces the risk of gastrointestinal hemorrhage. However, there is a discussion regarding possible PPI-dabigatran interaction that may reduce the efficacy of this therapy. To determine the impact of concomitant PPI on dabigatran plasma levels in patients with nonvalvular atrial fibrillation (NV-AF). A pilot prospective study in patients with NV-AF on dabigatran therapy was performed; 31 patients were enrolled. PPI with either omeprazole or pantoprazole was administrated in 19 patients. Blood samples were taken for the assessment of the dabigatran trough and peak levels. Dabigatran concentration was measured with the Hemoclot Thrombin Inhibitor Assay. There were significant differences in dabigatran trough level comparing patients treated with PPI and patients without PPI (58.86 ± 36.76 ng/mL vs. 110.72 ± 88.47 ng/mL, P < 0.05). Similarly, there were significant differences in dabigatran peak level between compared groups (88.0 ± 20.5 ng/mL vs. 174.4 ± 139.64 ng/mL, P < 0.05). This pilot study demonstrated the interaction between PPI and dabigatran levels in patients with NV-AF.

Use of dabigatran with antiretrovirals.

Theoretical and untested interactions between antiretrovirals and direct-acting oral anticoagulants have limited the use of this new class of anticoagulant in people with HIV infection. This case series, the first of its kind, reports on the successful concurrent use of the direct-acting oral anticoagulant dabigatran and antiretroviral therapy. This series involved 14 patients requiring anticoagulation for management of atrial fibrillation, who were either unable or unwilling to take warfarin, and who were receiving concurrent treatment for HIV infection. Participants were treated with dabigatran with dose monitoring to establish the safety and efficacy of concurrent use with antiretrovirals. All were commenced on 110mg twice daily, increased to 150mg twice daily if the trough level was < 69.3ng/mL. In the 14 patients treated with dabigatran and antiretrovirals, there were no thromboembolic or bleeding complications. Dabigatran treatment was discontinued in one patient because of undetectable dabigatran levels despite dose escalation. Dabigatran levels fell within the fivefold variance seen in the Randomized Evaluation of Long-Term Anticoagulation Therapy (RE-LY) study at a dose of either 110 or 150 mg twice daily. This case series represents the largest published population to date successfully receiving antiretroviral and direct-acting oral anticoagulant therapy. Given the significant health care burden faced by people living with HIV, the availability of safe anticoagulant therapy without the requirement for monitoring is an important option in this patient population.

Reduced Dose Direct Oral Anticoagulants in Older Adults with Atrial Fibrillation

Doses of direct oral anticoagulants (DOACs) are often reduced in older adults based on age, renal function, and bleeding risk. This review assesses recent evidence for safety and efficacy of reduced dose DOAC regimens in older adults. Dabigatran 110 mg twice daily shows similar efficacy and similar or lower bleeding risk compared to 150 mg twice daily in several studies. Dabigatran 110 mg is approved outside the USA and can be considered in ages > 75–80, or in patients with a propensity for higher dabigatran blood levels. Rivaroxaban 15 mg, apixaban 2.5 mg, and edoxaban 30 mg are safe and effective when used appropriately in patients who qualify based on labeled dosing. Limited evidence suggests inappropriately dose-reduced DOACs may increase risk for thromboembolic events. Besides dabigatran, dose reduction of apixaban, rivaroxaban, and edoxaban should be limited to patients who qualify based on FDA-approved parameters. The risk of stroke and bleeding should be carefully considered and discussed with each patient when deciding whether to reduce a DOAC dose off-label.

Pharmacogenomics of Novel Direct Oral Anticoagulants: Newly Identified Genes and Genetic Variants.

Direct oral anticoagulants (DOAC) have shown an upward prescribing trend in recent years due to favorable pharmacokinetics and pharmacodynamics without requirement for routine coagulation monitoring. However, recent studies have documented inter-individual variability in plasma drug levels of DOACs. Pharmacogenomics of DOACs is a relatively new area of research. There is a need to understand the role of pharmacogenomics in the interpatient variability of the four most commonly prescribed DOACs, namely dabigatran, rivaroxaban, apixaban, and edoxaban. We performed an extensive search of recently published research articles including clinical trials and in-vitro studies in PubMed, particularly those focusing on genetic loci, single nucleotide polymorphisms (SNPs), and DNA polymorphisms, and their effect on inter-individual variation of DOACs. Additionally, we also focused on commonly associated drug-drug interactions of DOACs. CES1 and ABCB1 SNPs are the most common documented genetic variants that contribute to alteration in peak and trough levels of dabigatran with demonstrated clinical impact. ABCB1 SNPs are implicated in alteration of plasma drug levels of rivaroxaban and apixaban. Studies conducted with factor Xa, ABCB1, SLCOB1, CYP2C9, and VKORC1 genetic variants did not reveal any significant association with plasma drug levels of edoxaban. Pharmacokinetic drug-drug interactions of dabigatran are mainly mediated by p-glycoprotein. Strong inhibitors and inducers of CYP3A4 and p-glycoprotein should be avoided in patients treated with rivaroxaban, apixaban, and edoxaban. We conclude that some of the inter-individual variability of DOACs can be attributed to alteration of genetic variants of gene loci and drug-drug interactions. Future research should be focused on exploring new genetic variants, their effect, and molecular mechanisms that contribute to alteration of plasma levels of DOACs.

Volume replacement strategies do not impair the binding of dabigatran to idarucizumab: Porcine model of hemodilution.

BackgroundIdarucizumab is a humanized Fab fragment that specifically reverses dabigatran anticoagulation. In trauma, volume expanders are used for resuscitation to compensate for blood loss and hemorrhagic shock, but it is unknown whether volume expanders influence the binding of dabigatran to its antidote. Using a porcine dilutional coagulopathy model, this study investigated whether volume replacement strategies affect binding of dabigatran to idarucizumab.MethodsTwenty-five male pigs were treated orally with dabigatran etexilate (30 mg/kg bid) for 3 days. The following day, animals were anesthetized, infused with dabigatran (total dose 0.645 mg/kg) to achieve supratherapeutic concentrations, and randomized 1:1:1:1:1 (n = 5 per group) to control (no hemodilution) or hemodilution where ~50% of blood volume was substituted with Ringer’s solution, 6% hydroxyethyl starch 130/0.4, 6% hydroxyethyl starch 200/0.5 or 4% gelatin. Idarucizumab was then administered intravenously (30 mg/kg) and serial blood samples were taken for up to 24 hours to measure diluted thrombin time (corresponding with dabigatran activity), total dabigatran (bound to antidote and free drug) and a panel of coagulation parameters.ResultsMean plasma dabigatran levels were 617 ± 16 ng/mL after infusion and 600 ± 114 ng/mL after ~50% hemodilution with no significant differences between groups. Following treatment with idarucizumab, plasma concentrations of unbound dabigatran decreased markedly, with similar reductions in all groups. Dabigatran-induced prolongation of coagulation parameters was rapidly reversed in all groups.ConclusionThis study indicates that several volume expanders used for resuscitation in trauma do not interfere with the binding of idarucizumab to dabigatran.

Assessment of direct oral anticoagulant assay use in clinical practice.

There are no clear and consistent guidelines on how to utilize DOAC assays, and reports on the use of DOAC levels in clinical practice is limited. The objective of this study was to analyze why DOAC levels are ordered, how the results affect clinical decision-making, and to determine if DOAC assays are utilized appropriately. This was a retrospective chart review study analyzing 150 dabigatran, rivaroxaban, and apixaban levels performed at a single institution. The majority of DOAC assays were ordered in situations or special patient populations where confirming absence or detecting presence of drug may be useful. The most common indication for ordering assays was prior to an invasive procedure. Most DOAC levels were timed appropriately but peak levels were most likely to be incorrectly ordered. Clinical decisions following level results depended on indication for ordering and were most commonly used to determine whether or not to proceed with an invasive procedure. The results of our study suggest while DOAC assays are generally ordered for useful indications, there is still a lack of understanding of when levels should be drawn and how to interpret DOAC assay results.

A level-headed approach to measuring direct oral anticoagulants: A 2-year retrospective analysis of DOAC levels from a tertiary UK centre.

Direct oral anticoagulants (DOAC) are commonly prescribed and measuring drug levels may be useful in a number of contexts. However, data on DOAC level measurement and their clinical utility in real-world studies are limited. We carried out a 2-year retrospective cohort study of DOAC levels measured at our institution. One hundred and sixty-nine levels measured in 113 patients were included in the final analysis. Our patients had a median age of 69.9. AF was the commonest indication for anticoagulation. Median turnaround time for inpatient levels was 92minutes. Median FXa inhibitor levels within 6hours of last dose and following one half-life were similar to those described previously. However, the range of levels was wider than expected. Importantly, some levels remained in an on therapy range even after 3 half-lives. There was no correlation between dabigatran level and time from last dose. The reason for request varied with setting; 23 outpatient levels were to monitor drug efficacy, whereas 54 and 43 inpatient levels were collected in the context of bleeding and emergency surgery respectively. 60.3% of levels had an impact on clinical decision making. Our real-world study demonstrates that DOAC levels can be performed in a timely manner to influence clinical decision making. In addition, it suggests there is a wide variation in levels such that it can be difficult to predict in the real world. Overall, this supports the wider use of DOAC levels to help guide clinicians in managing patients taking these drugs.

Basic coagulation tests as surrogates of dabigatran levels in a pre-operative setting: Analysis of five activated partial thromboplastin time reagents and thrombin time

BackgroundIn patients who are receiving dabigatran, a direct oral anticoagulant, measuring the anticoagulant effect before surgery may be needed in certain circumstances. Although the dilute thrombin time (dTT) can reliably measure dabigatran levels, it is not consistently available. More commonly used coagulation tests, including the activated partial thromboplastin time (aPTT) and thrombin time (TT) might have clinical utility but their accuracy is uncertain. Methods103 patients stopped dabigatran 1–4 days before an elective surgery/procedure as part of a standardized dabigatran interruption protocol. With a blood sample taken just before surgery, we assessed the accuracy of five aPTT assays (Actin FS, Stago PTT, C.K. PREST, HemosIL aPTT-SP, SynthASil) and TT to measure the residual anticoagulant effect of dabigatran. We determined the sensitivity, specificity and other accuracy indices of these assays to predict a dabigatran level > 30 ng/mL as determined by a reference standard test, the dTT (Hemoclot). ResultsOf five aPTT reagents, four assays had excellent (100%) and one assay had good (93%) sensitivity to detect a level of dabigatran > 30 ng/mL, but all had insufficient specificity (50–74%). A TT > 90 s had good sensitivity (93%) and excellent specificity (100%). ConclusionFive aPTT assays had good sensitivity but poor specificity to detect low levels of dabigatran (≤30 ng/mL) after standardized dabigatran interruption before an elective surgery/procedure, thereby limiting the use of aPTT as an alternative to the dTT in preoperative settings.

Drug interaction as a predictor of direct oral anticoagulant drug levels in atrial fibrillation patients.

Data are limited on the effects of drug interactions on direct-acting oral anticoagulant (DOAC) levels. We evaluated the effects of the use of interacting drugs on DOAC levels in patients with atrial fibrillation (AF). We reviewed data of AF patients tested for DOAC levels in 2013-2017. The primary outcomes were drug levels exceeding the expected steady-state range, and in the highest quartile. A multivariate analysis was performed to evaluate the correlation of treatment by the use of interacting drugs, CYP3A4 and P-glycoprotein (P-gp) inhibitors, with the primary outcomes. Overall, 147 patients underwent DOAC level measurement [dabigatran (n = 31), rivaroxaban (n = 29), apixaban (n = 87)]. Thirty-three (22.4%) had drug levels exceeding the expected range. Seventy-nine (53.7%) patients were treated with at least one interacting drug. In multivariate analysis, the concomitant use of interacting drugs was an independent predictor for drug levels exceeding the expected range (OR 3.3, 95% CI 1.20-9.05). The defined daily dose of the interacting drug correlated positively with DOAC levels (r = 0.29, P = 0.001). Co-treatment with interacting drugs was associated with extremely high levels of dabigatran, (OR 16.6, 95% CI 1.29-215.18) but not of the other DOAC examined. Concomitant use of interacting drugs is associated with high DOAC levels in patients with AF. Further investigation is warranted to establish the differences between specific DOAC, evaluate the effect on patient outcomes, and characterize the role of DOAC monitoring in this setting.

The fibrinogen prothrombin time‐derived method is not useful in patients anticoagulated with low molecular weight heparins or rivaroxaban

Background The fibrinogen prothrombin time-derived (FIBPT-d) method with photo-optical coagulometers is easy and economical. However, there are few reports on the behavior of this test on samples from patients anticoagulated with direct oral anticoagulants or low molecular weight heparin (LMWH). Objective To compare fibrinogen results obtained with the Clauss (FIB C) method and the FIBPT-d method with two thromboplastins in anticoagulated patients. Population The study population comprised 295 consecutive anticoagulated patients: 99 treated with vitamin K antagonists (VKAs), 49 treated with unfractionated heparin (UFH), 47 treated with LMWH, 50 treated with rivaroxaban, 50 treated with dabigatran, and 100 normal controls (NCs). Methods Dabigatran samples were analyzed by the use of FIB C with HemosIL Fibrinogen C or 100 NHI thrombin units mL-1 reagents; rabbit brain and human recombinant thromboplastins with HemosIL PTFibrinogen HS plus (HS) and Recombiplastin 2G (RP) were used for FIBPT-d method. Heparin and rivaroxaban levels were assessed with HemosIL Liq antiXa with specific calibrators; dabigatran levels were determined with the HemosIL Direct Thrombin Inhibitor Assay. All assays were performed on the ACL TOP platform in two laboratories. Percentage biases for the FIBPT-d method versus the FIB C method were calculated by the use of Bland-Altman plots. Results Positive biases of the FIBPT-d method versus the FIB C method with both thromboplastins were seen in NC samples (13.7% and 18.9% for HS and RP, respectively), but biases with HS in rivaroxaban and VKA patient samples were higher than that in NC samples, at 31.9% and 34.0%, respectively. LMWH patient samples showed higher bias than NC samples: 26.5% and 29.3.0% with HS and RP, respectively. UFH and dabigatran patient samples showed similar bias as NC samples. Conclusion The FIBPT-d method should not be used in anticoagulated patients, because the FIBPT-d mathematical algorithm has been validated only in normal subjects, so overestimation could occur in these patients.

Dabigatran Levels in Elderly Patients with Atrial Fibrillation: First Post-Marketing Experiences.

The number of elderly individuals with non-valvular atrial fibrillation (NV-AF) requiring long-term anticoagulation is rising. The pharmacokinetics of oral anticoagulants in elderly individuals may differ from that for younger patients. The aim of this study was to assess the dabigatran levels in elderly patients with NV-AF. A pilot prospective post-marketing study in patients with NV-AF on dabigatran therapy was performed; we enrolled 21 consecutive elderly patients (aged ≥ 75years) on a reduced dabigatran regimen (110mg twice daily) and compared them with 13 younger (≤ 70years) individuals on reduced dabigatran therapy due to renal impairment and with 16 younger patients on standard dabigatran therapy (150mg twice daily). Blood samples were taken for the assessment of dabigatran trough and peak levels. Dabigatran levels were measured with the Hemoclot® Thrombin Inhibitor Assay. There were significant differences in dabigatran trough levels when comparing elderly patients on reduced dabigatran with non-elderly patients on reduced dabigatran (99.3 ± 73.6 vs 51.6 ± 25.6ng/mL; p < 0.01). Similarly, the detected dabigatran peak levels were significantly higher in elderly patients on reduced dabigatran compared with non-elderly patients on reduced dabigatran (173.4 ± 116.2 vs 116.1 ± 19.1ng/mL; p < 0.01). No significant differences in dabigatran trough and peak levels were found when comparing elderly patients on reduced dabigatran with non-elderly patients on standard dabigatran therapy. This pilot study demonstrated that elderly patients on reduced dabigatran exhibit significantly higher dabigatran levels than younger individuals on a reduced regimen, and similar levels compared with younger individuals on standard dabigatran.

The effect of dabigatran on thrombin generation and coagulation assays in rabbit and human plasma

ObjectivesDabigatran etexilate is widely used for stroke prevention in the patients with atrial fibrillation. The anticoagulation activity of dabigatran is not necessary monitored in routine clinical practice. We aimed to study the effect of dabigatran on thrombin generation (TG) and coagulation assays in rabbit and human plasma. MethodsRabbits received different concentrations of dabigatran etexilate (5 mg/kg, 10 mg/kg). Patients with atrial fibrillation took 110 mg dabigatran etexilate twice daily. The concentrations of dabigatran in rabbit and human plasma were detected by liquid chromatography/tandem mass spectrometry (LC-MS/MS) and ecarin chromogenic assay (ECA). The relationship between plasma dabigatran concentrations and the activated partial thromboplastin time (aPTT), prothrombin time (PT), thrombin time (TT), and TG were evaluated. ResultsThere was strong correlation between LC-MS/MS and ECA (P < 0.001). Bland Altman analysis demonstrated that ECA assay could accurately predict human plasma dabigatran concentrations whereas underestimate the plasma concentrations of dabigatran in rabbits. Both the PT and the aPTT assays showed low correlations with dabigatran. The TT assay was highly sensitive to dabigatran levels. Low concentrations of dabigatran paradoxically increased TG. ConclusionsLC-MS/MS is the gold standard for detecting the concentrations of dabigatran. ECA correlates well with LC-MS/MS. The coagulation assays depend more on other factors. Paradoxical enhancement of TG may predict clinically rebound hypercoagulability and warrants further exploration.

Point of Care Testing (POCT) to assess drug concentration in patients treated with non-vitamin K antagonist oral anticoagulants (NOACs)

BackgroundNon–vitamin K antagonist oral anticoagulants (NOACs) do not need routine laboratory monitoring but measurement of drug concentration is important in emergency conditions. Specific laboratory tests are not readily available or not implemented in every hospital. Point-of-Care Tests (POCT) may bridge this gap and be used as a bedside solution. ObjectivesFeasibility of POCT to assess plasma levels of dabigatran, rivaroxaban and apixaban. Patients/methodsActivated Coagulation Time-Low Range (ACT - LR) using a portable Hemochron Signature Elite for dabigatran and prothrombin time (expressed as INR) by Coaguchek XS Pro for rivaroxaban and apixaban were obtained at trough and peak in 136 consecutive patients taking NOACs (70 on dabigatran, 45 on rivaroxaban and 20 on apixaban). Using a paired study design, drug concentrations were concurrently determined by functional specific tests. Results and conclusionsThe correlation between NOACs concentration and the values obtained using the POCTs was high for dabigatran and rivaroxaban (r = 0.80 and r = 0.82, respectively) and low for apixaban (r = 0.21). ACT-LR ≤ 188 s better detected dabigatran levels ≤ 50 ng/ml, with a sensitivity of 87.5% and a specificity of 84.1%. ACT-LR values > 217 s better discriminated value of dabigatran > 200 ng/ml, with a sensitivity of 86.7% and a specificity of 81.4%. INR Coaguchek values ≤ 1.2 better identified patients with rivaroxaban values < 100 ng/ml, with sensitivity of 90%, specificity of 88.5%. This analysis was not possible for apixaban. ConclusionIn emergency situations POCT use may provide useful immediate information on dabigatran and rivaroxaban concentration.

Detecting clinically relevant rivaroxaban or dabigatran levels by routine coagulation tests or thromboelastography in a cohort of patients with atrial fibrillation

BackgroundTraditional coagulation tests are included in emergency guidelines for management of patients on direct oral anticoagulants (DOACs) who experience acute bleeding or require surgery. We determined the ability of traditional coagulation tests and fast whole blood thromboelastography (ROTEM®) to screen for anticoagulation activity of dabigatran and rivaroxaban as low as 30 ng/mL.MethodsOne hundred eighty-four citrated blood samples (75 dabigatran, 109 rivaroxaban) were collected from patients with non-valvular atrial fibrillation (NVAF), to perform screening tests from different manufacturers, (diluted, D) PT, aPTT, TT and ROTEM®. The activity of DOACs was quantitatively determined by clot detection assays: Hemoclot DTT and DiXaI test (Biophen), on CS2100 (Siemens). The clotting time (CT) of INTEM and EXTEM ROTEM® (Werfen) were used as test parameters.ResultsDabigatran, ≥ 30 ng/mL, was accurately detected by five coagulation tests: APTT Actin FSL (93%), PT Neoplastin (93%), APTT Cephascreen, Thromboclotin, and Thrombin (all 100%), but not by PT Innovin (49%). CT-EXTEM (91%) was sufficiently sensitive, but not CT-INTEM (52%). APTT Cephascreen and Thrombin showed good linearity (R2 = 0.71,R2 = 0.72). For the other tests linearity was moderate to poor. Rivaroxaban was accurately detected by PT Neoplastin (98%) and less so by APTT Cephascreen (85%). In addition, rivaroxaban was also accurately detected by CT-INTEM (96%). PT Neoplastin showed good linearity (R2 = 0.81), all other tests had moderate to poor linearity.ConclusionIn patients with NVAF, the ability of routine coagulation tests to detect the presence of significant levels of DOACs is test and reagent dependent. CT-INTEM and CT-EXTEM may be fast whole blood alternatives.Trial registrationThe Institutional Review Board of the MUMC approved this study (December 2011, project number 114069).

Abstract TMP110: The Correlation of Through Plasmatic Concentration of Dabigatran and CES1 Genotype With Major Bleeding in Stroke Patients

Introduction: Dabigatran is direct thrombin inhibitor approved in the prevention of stroke in patients with atrial fibrillation. It was shown in the RELY trial substudy that genetic variants could contribute to interindividual variability in concentrations of the active metabolite of dabigatran and influence the safety of treatment. Carriage of the CES1 rs2244613 minor allele was associated with lower exposure to active metabolite and with a lower bleeding risk compared to wild-type allele. Aim: To determine the influence of gene CES1 polymorphism rs2244613 and through plasmatic concentration of dabigatran on occurrence of major bleeding in stroke patients. Methods: Prospective observational monocentric study in consenting stroke patients initiated on dabigatran. Primary outcome was major bleeding defined using ISTH criteria. DNA analysis of CES1 polymorphism rs2244613 was done with RFLP analysis. Through concentration of dabigatran was measured with liquid chromatography-tandem mass spectrometry (LC-MS/MS) at least 7 days after initiation. Results: 110 patients after cardioembolic stroke, mean age 70,2 (SD 12.7), 56 (50.9%) women, were enrolled. Mean follow-up time was 19.9 months (total 182.2 patient years). 68 (61.8%) patients were wild-type, 37 (33.6%) were minor allele heterozygotes and 5 (4.5%) were homozygous minor allele carriers. Through dabigatran concentration were non-significantly lower in minor allele carriers: 132.8 (SD 98.7) ng/ml in wild-type patients, 112.2 (80.0) in heterozygotes and 95.6 (SD 88.1) in homozygotes. There were 6 episodes of major bleeding, all in patients with wild-type genotype. The patients with dabigatran level above 160 ng/ml (upper quartile) were more likely to have major bleeding, HR 5.74 (95% CI 1.05 - 31.42, p = 0.044). Age and renal function did not correlate with the bleeding. Conclusion: Patients with higher dabigatran concentration had significantly higher major bleeding risk. Minor allele carriers had non-significant trend for having lower through dabigatran level. Personalized dabigatran dosing based on pharmacogenetics and monitoring plasmatic levels should be studied in future trials with the aim to increase the safety of treatment.

The anticoagulant effect of therapeutic levels of dabigatran in atrial fibrillation evaluated by thrombelastography (TEG®), Hemoclot Thrombin Inhibitor (HTI) assay and Ecarin Clotting Time (ECT)

Monitoring the effect of dabigatran (Pradaxa®) is challenging. The aim of this study was to evaluate if thrombelastography reaction time (TEG® R) could detect the anticoagulant effect of dabigatran showing a correlation between TEG® R, Hemoclot Thrombin Inhibitor (HTI) assay and Ecarin Clotting Time (ECT) in patients with non-valvular atrial fibrillation (NVAF). Blood samples from 35 AF patients receiving either 110 mg (n 19) or 150 mg (n 16) dabigatran twice daily were analyzed with TEG®, HTI and ECT 2–3 h after dabigatran intake. All patients had prolonged TEG® R. The patients receiving dabigatran 110 mg ×2 had a TEG® R mean 14.2 min (range 9.1–25), a mean dabigatran concentration measured by HTI of 268.5 ng/mL (range 54–837 ng/mL) and by ECT of 355.7 ng/mL (range 40–1020 ng/mL). The corresponding numbers for patients receiving dabigatran 150 mg ×2 were TEG® R mean of 12.5 min (range 9.2–23.2 min), mean dabigatran concentration of 179.2 ng/mL by HTI (range 26–687 ng/mL) and by ECT 225.1 ng/mL (range 42–1020 ng/mL). The two dosage groups had comparable anticoagulation demonstrated by equally prolonged TEG® R (p = .909), HTI (p = .707) and ECT (p = .567). No difference in creatinine levels in the two dosage groups was observed (p = .204) though patients with dabigatran concentration >400 ng/mL had significantly higher creatinine levels (p = .001). Large individual variation of the anticoagulant response was observed. Some patients had TEG® R values up to three times upper normal limit with immediate risk of bleeding. Our data indicate that TEG® R reflected dabigatran levels in NVAF patients and that TEG® R correlated to HTI and ECT.

Impact of four direct oral anticoagulants on rotational thromboelastometry (ROTEM).

Rotational Thromboelastometry (ROTEM) is a point of care method used to monitor coagulation during surgery and to guide transfusion strategies in patients presenting with severe bleeding. The aim of our study was to determine the impact of four direct oral anticoagulants (DOACs) on 3 commonly used ROTEM tests. Whole blood samples from 20 healthy donors were spiked in vitro with apixaban, edoxaban, rivaroxaban or dabigatran at 5 different plasma concentrations (0-1000ng/mL). EXTEM, INTEM and FIBTEM tests were systematically performed. There was a linear relationship between the increase in clotting time (CT) and plasma DOAC concentrations in both the EXTEM and INTEM tests. We found that the DOAC concentration required to double EXTEM CT was 1042±225ng/mL for apixaban, 134±38ng/mL for edoxaban, 176±26ng/mL for rivaroxaban and 284±73ng/mL for dabigatran. INTEM CT was less sensitive than EXTEM CT whatever the anticoagulant. EXTEM CT was above the normal range for 5 of 5 spiked samples when the plasma concentrations were ~1000ng/mL for apixaban, ~100ng/mL for edoxaban, ~200ng/mL for rivaroxaban and ~200ng/mL for dabigatran. Maximum Clot Firmness in EXTEM, INTEM and FIBTEM tests was not affected whatever the DOAC or its concentration. This study found a DOAC dose-dependent increase in ROTEM CTs. ROTEM tests were only poorly impacted by low levels of edoxaban, rivaroxaban or dabigatran. Apixaban had only a low effect even at high concentrations.

Dabigatran reduces thrombin-induced platelet aggregation and activation in a dose-dependent manner.

Dabigatran is an oral anticoagulant and a reversible inhibitor of thrombin. Further, dabigatran might affect platelet function through a direct effect on platelet thrombin receptors. The aim was to investigate the effect of dabigatran on platelet activation and platelet aggregation. Healthy donor blood was incubated with dabigatran 0, 50, 500ng/mL, corresponding to the therapeutic range of dabigatran peak plasma concentrations, and 10,000ng/mL comprising a supra-therapeutic dabigatran plasma level. Platelet aggregation was tested with 96-well aggregometry. Flow cytometry was used to test platelet activation and platelet thrombin receptor expression (SPAN-12 and WEDE-15 expression). Agonists were thrombin, thrombin receptor-activating peptide, protease-activated receptor-4 agonist, collagen, collagen-related peptide, arachidonic acid, and adenosine diphosphate. All concentrations of dabigatran fully inhibited platelet aggregation for thrombin up to 2IU/mL, while dabigatran did not affect platelet aggregation by other agonists. Platelet activation (percentage of platelets positive for activated GPIIb/IIIa, CD63, P-selectin) was reduced after thrombin stimulation in samples with dabigatran levels ≥500ng/mL. After stimulation with thrombin, the percentage of activated GPIIb/IIIa-positive platelets was 99.8 ± 0.2% without dabigatran, 14.7 ± 4.7% with 500ng/mL dabigatran, and 4.2 ± 0.2% with 10,000ng/mL dabigatran, both p < 0.001 when compared to samples without dabigatran. Also, the receptor expression of GPIIb/IIIa, CD63, andP-selectin were reduced after dabigatran treatment. The expression of thrombin receptors was reduced at dabigatran on ≥ 500ng/mL. In conclusion, dabigatran exclusively inhibits thrombin-induced platelet activation and aggregation with a dose-dependent response. Platelet stimulation with other agonists was not affected by dabigatran.

Laboratory measurement of the direct oral anticoagulants: Indications and impact on management in clinical practice.

Although the direct oral anticoagulants (DOACs) do not require routine laboratory monitoring, there may be special situations in which measurement of drug levels is desirable. There is a paucity of information on how measurement of DOAC levels is used in clinical practice. We conducted a retrospective cohort study of dabigatran, rivaroxaban, and apixaban levels measured at our institution. Of 9793 patients with an active prescription for dabigatran, rivaroxaban, or apixaban in the electronic medical record during the 2.5-year study period, 32 (0.33%) patients underwent a total of 37 DOAC measurements. Twenty patients were on rivaroxaban, 12 were on apixaban, and none was on dabigatran. The most common indications for measurement in inpatients were surgery, breakthrough thrombosis, and bleeding. In the ambulatory setting, patient characteristics suspected to lead to derangements in drug levels (eg, extremes of body weight, gastrointestinal malabsorptive disorders) served as a frequent indication. Among preoperative patients, DOAC levels influenced decisions about the timing of surgery. In most outpatients, levels were within expected ranges and affirmed current management. In a small number of patients with breakthrough thrombosis or bleeding, the identification of drug levels below or above expected concentrations led to a change in the anticoagulant regimen. In conclusion, DOAC measurement was infrequently requested. Indications differed between hospitalized patients and outpatients. Clinical response varied by drug level and indication.