Dabigatran Accumulation Research Articles

Dabigatran accumulation in acute kidney injury: is more better than less to prevent bleeding? A case report

Dabigatran is an oral anticoagulant that is mainly renally excreted. Despite its efficacy in preventing thromboembolic events, concerns arise regarding bleeding complications in patients with acute kidney injury. Idarucizumab is its specific antidote and reverses quickly and effectively dabigatran anticoagulation effects in situations of severe bleeding or pending surgical procedures, but its benefit beyond these two indications remains uncertain. We present a case of a woman with atrial fibrillation anticoagulated by dabigatran and admitted with Streptococcus agalactiae meningitis, acute kidney injury and dabigatran accumulation. Idarucizumab was not administered initially as she did not meet its current strict indications. However, subsequently, significant bleeding necessitated its use. A rebound increase in dabigatran concentration was associated with an intracranial hemorrhage, but the combination of additional doses of idarucizumab with hemodialysis lowered the dabigatran concentration and prevented significant rebound increases. Further investigation into the optimal management of dabigatran accumulation and acute kidney injury-associated bleeding is needed to enhance patient outcomes and safety. Early initiation of hemodialysis together with idarucizumab administration may be crucial in preventing life-threatening bleeding events in these patients.

Development and Validation of a Chromogenic Direct Thrombin Inhibitor Assay on the ACL Top 700 for Quantifying Dabigatran Levels in Plasma

Dabigatran is a potent, competitive, and reversible direct thrombin inhibitor, that binds to the active site of thrombin, inhibiting both free and clot-bound thrombin. It is the active form of dabigatran etexilate, which is a low molecular weight prodrug metabolized to its active form after oral administration. Although patients on therapeutic doses of dabigatran do not require routine coagulation monitoring due to its dose dependent and predictable pharmacological profile, there may be situations in which it may be beneficial to be able to accurately measure the degree of anticoagulation (ie. urgent surgery, severe bleeding, thrombosis despite treatment, overdose, bridging with other anticoagulants, patients with a high risk of dabigatran accumulation or potential drug interactions). Accordingly, we developed and validated a chromogenic direct thrombin inhibitor assay on the ACL TOP 700 automated hemostasis analyzer for quantifying dabigatran levels in human plasma.Our test principle was based on the in vitro thrombin inhibition by dabigatran, in which excess thrombin was added to the plasma sample, the thrombin in the sample was neutralized in proportion to the amount of dabigatran, and the residual thrombin hydrolyzed the chromogenic substrate releasing pNA which was measured photometrically at 405 nm on the ACL TOP 700. This assay was calibrated with purchased dabigatran calibration samples (Aniara). Each calibration curve consisted of five points, used a 3rd order polynomial curve fit, and was performed each time an assay was run. For all runs, an r2 of 1.0 was observed and all calibrators demonstrated an acceptable accuracy and precision (± 10% from assigned value for samples ≥ 100 ng/mL or < 10 ng/mL of assigned values for all other samples).Validation of this dabigatran level assay for accuracy, intra- and inter-assay precision, analytical specificity, analytical sensitivity, analyte stability, and robustness was completed and reportable result ranges established. To evaluate accuracy, three plasma samples containing dabigatran in the range of expected concentrations (high, medium, low) were compared to the value determined by mass spectrometry. Intra- and inter-assay precision was determined by analyzing these 3 samples over multiple assay runs spanning multiple days. All determined values were within 15% of the assigned values for samples ≥ 100ng/mL and within 10ng/mL of the assigned values for all other samples. Analytical specificity was confirmed by running sample pairs (plasma/serum, citrate/EDTA, hemolyzed/non-hemolyzed, icteric/non-icteric, lipemic/cleared-lipemic, 1 U/mL unfractionated heparin and 2 U/mL low molecular weight heparin-containing samples). Only the serum sample resulted in >10% difference from the standard plasma, indicating assay interference. Assay results were not affected by unfractionated heparin up to 1 U/mL and low molecular weight heparin up to 2 U/mL. Analytical sensitivity was established by assaying normal plasma containing no or low levels of dabigatran. The limit of blank was determined to be 3 ng/mL, limit of detection 10 ng/mL, and limit of quantitation (LoQ) 20 ng/mL. Analyte stability studies established samples thawed and refrozen up to 2 times were acceptable. Assay robustness was determined to be acceptable. The reportable range was determined to be 20-900 ng/mL based on the calibration curve and LoQ.In summary, we have developed and validated an accurate, precise, sensitive and robust chromogenic assay on the ACL TOP 700 for the determination of dabigatran concentration in human plasma. This assay may prove useful in certain clinical circumstances (urgent surgery, severe bleeding, or thrombosis despite treatment) for the assessment of anticoagulation status. DisclosuresNo relevant conflicts of interest to declare.

Response to Letters Regarding Article, “Periprocedural Bleeding and Thromboembolic Events With Dabigatran Compared With Warfarin: Results From the Randomized Evaluation of Long-Term Anticoagulation Therapy (RE-LY) Randomized Trial”

RE-LY is the largest randomized experience reporting outcomes after interruption of anticoagulant therapy.1 There was no excess of bleeding in patients taking dabigatran, including those having major or urgent surgery.1 David and colleagues correctly state that the majority of procedures performed during the RE-LY trial were minor. Nonetheless, our analysis included 1482 major procedures that had a 6% to 8% rate of major bleeding,1 which was numerically lower among dabigatran-treated patients.1 Hjemdahl et al opine that the high rate of major bleeding in RE-LY patients assigned to dabigatran 150 mg twice daily who had interruption for >72 hours before surgery suggests accumulation of dabigatran in patients with renal impairment. However, data from RE-LY do not support this interpretation, because the same pattern …

Dabigatran monitoring made simple?

Haemost 2013; 110: 308-315. Dabigatran, an oral thrombin inhibitor, is licensed as an alternative to warfarin for stroke prevention in patients with atrial fibrillation. As the first of the new oral anticoagulants (NOACs) to gain approval for this indication, its use is increasing now that its safety has been confirmed using real-world data (1, 2), and clinical guidelines have given preference to NOACs over warfarin for stroke prevention in patients with atrial fibrillation (3-5). Although dabigatran was designed to be given in fixed doses without monitoring, there are situations where assessment of its anticoagulant activity can be helpful (6). For example, detection of little or no dabigatran activity in plasma may identify patients who can safely undergo surgery, or receive thrombolytic therapy for management of acute ischaemic stroke. Conversely, excessive anticoagulant activity may indicate dabigatran accumulation in patients with deteriorating renal function, or may influence therapy in those with serious bleeding; common concerns in everyday clinical practice (6, 7). These scenarios highlight the need for simple, rapid and widely available monitoring tests for dabigatran. How can the anticoagulant activity of dabigatran be assessed? Dabigatran prolongs the activated partial thromboplastin time (aPTT) more than the prothrombin time (▶ Table 1). Although the effect of dabigatran on the aPTT is concentrationdependent, the aPTT begins to plateau with plasma dabigatran concentrations above 200 ng/ml (8-12). The thrombin time is very sensitive to dabigatran and even low concentrations of dabigatran produce a marked prolongation in the thrombin time. Dilution of the plasma prior to thrombin time determination renders the test less sensitive to dabigatran. The Hemoclot assay capitalises on this phenomenon; to perform this test, patient plasma is diluted eight-fold prior to thrombin time determination (13). The plasma dabigatran concentration is then calculated by reference to a standard curve constructed using dabigatran calibrators. Although the test is rapid and simple, the Hemoclot assay is only available in specialised coagulation laboratories, and the test is not licensed for patient use in the United States. The ecarin clotting time can also be used to determine plasma dabigatran concentrations, but this test is even less widely available than the Hemoclot assay. How do these coagulation tests perform in the real world setting? This is the focus of the study by Hapgood et al. (14) in a recent issue of Thrombosis and Haemostasis. These investigators used the Hemoclot assay to determine drug concentrations in 75 plasma samples collected from 45 patients taking dabigatran. Dabigatran levels were then correlated with the aPTT, which was performed with four different reagents. Using linear regression analysis, they determined the aPTT range with each reagent that corresponded to dabigatran levels of 90 to 180 ng/ml; the range that the authors designated as therapeutic for dabigatran. The thrombin time also was correlated with dabigatran concentrations. Dabigatran concentrations over 60 ng/ml were associated with marked prolongation of the thrombin time; a finding that highlights the responsiveness of this test to dabigatran. Although the study design is straightforward, do plasma concentrations of 90 to 180 ng/ml really represent the therapeutic range for dabigatran? As outlined by the authors, these values reflect the median trough and peak concentrations of dabigatran determined in subjects given the drug at a dose of 150 mg twice daily (15). However, the corresponding values in those taking 110 mg twice daily -the dabigatran dose used in at least 50% of patients in most countries -are about 65 and 130 ng/ml, respectively (16). Furthermore, even if the median trough and peak levels with the 150 mg dose of dabigatran are 90 and 180 ng/ml, respectively, this means that half of the patients will have dabigatran levels lower or higher than these values at trough and peak, respectively; findings that will complicate interpretation of aPTT results calibrated to this range. Therefore, 90 to 180 ng/ml cannot be considered the therapeutic range for dabigatran. What can we learn from this study? The authors show that the aPTT values obtained with dabigatran concentrations ranging from 90 to 180 ng/ml differ with each of the aPTT reagents examined; a finding consistent with previous reports that aPTT reagents vary in their responsiveness to the anticoagulant effects of dabigatran (9-12). In addition to confirming this finding in samples collected from patients taking dabigatran, the results of this study suggest that each laboratory will need to determine the sensitivity of its aPTT reagent to dabigatran; a process analogous to determining the aPTT range that corresponds to therapeutic anti-Xa levels for heparin whenever the aPTT reagent lot number changes. It is uncertain whether

Treatment of Dabigatran-Associated Bleeding

Dabigatran etexilate is a competitive, direct thrombin inhibitor that works in the coagulation cascade to ultimately prevent thrombus formation. It is recommended by the 2012 American College of Chest Physicians evidence-based clinical practice guidelines as first-line therapy over vitamin k antagonists for long-term antithrombotic therapy in patients with paroxysmal or persistent nonrheumatic atrial fibrillation who are at intermediate to high risk of stroke and systemic embolism (grade 2B). However, serious postmarketing events involving life-threatening bleeding are emerging with no antidote for reversal of the anticoagulant effect being available for use. Potential reversal agents are being used in clinical practice with questionable efficacy and safety profiles. We report a case involving an 84-year-old male with acute kidney injury who developed life-threatening gastrointestinal and surgical site bleeding secondary to dabigatran accumulation. Use of the Naranjo probability scale indicated a probable cause between the bleeding event and dabigatran use. After discontinuation of drug therapy, fresh frozen plasma, recombinant coagulation factor VIIa, and cryoprecipitate were administered as potential reversal agents with negligible benefit. However, this patient appeared to slowly benefit with administration of continuous venovenous hemodialysis. Based upon our experience with this patient and literature review, the most effective treatment algorithm for dabigatran-associated bleeding may be to utilize hemodialysis initially.

Effects of the oral, direct thrombin inhibitor dabigatran on five common coagulation assays

Dabigatran is an oral, reversible thrombin inhibitor that has shown promising results in large clinical trials. Laboratory monitoring is not needed but the effects on common coagulation assays are incompletely known. Dabigatran was added to plasma from healthy subjects in the concentration range 0-1,000 μg/l and analysed using several reagents for activated thromboplastin time (APTT), prothrombin time (PT), fibrinogen, antithrombin, and activated protein C resistance. Typical trough concentrations are about 50 μg/l, peak concentrations 100-300 μg/l. At 100 μg/l all APTT-results were prolonged. The concentration required to double APTT ranged between 227 and 286 μg/l, the responses for all five reagents were similar. PT-reagents were much less affected with almost no samples above INR 1.2 at 100 μg/l. The effect was sample dilution dependent with PT Quick type more sensitive than PT Owren type methods. If a patient on dabigatran has prolonged APTT, >90 seconds, and Quick PT INR>2 or Owren PT INR>1.5 over-dosing or accumulation of dabigatran should be considered. Two of four fibrinogen reagents underestimated the fibrinogen concentration considerably at expected peak concentration. Methods based on inhibition of thrombin over-estimated the antithrombin concentration, but not Xa-based. The APC-resistance methods over-estimated the APC-ratio, which may lead to miss-classification of factor V Leiden patients as being normal. Different coagulation assays, and even different reagents within an assay group, display variable effects at therapeutic concentrations of dabigatran. Some of these assay variations are of clinical importance, thus knowledge is needed for a correct interpretation of results.