Assessing Direct Oral Anticoagulants in the Clinical Laboratory

Direct oral anticoagulants (DOACs) have significant advantages over vitamin K antagonists including lack of need for routine laboratory monitoring. However, assessment of DOAC effect and concentration may be important to guide clinical management including need for DOAC reversal, particularly in acute or emergent situations. In this manuscript, the authors describe tests to screen for DOAC presence and tests that have demonstrated equivalence to gold standard testing for quantifying DOAC exposure. They also discuss the effect of DOACs on other coagulation assays and strategies for monitoring unfractionated heparin in patients with concomitant DOAC exposure.

Development of a Rapid Qualitative Screen for Anticoagulant Presence

BACKGROUND

Direct oral anticoagulants (DOACs) and fondaparinux with stable pharmacokinetics are commonly used anticoagulants for outpatient care. Due to the lack of monitoring requirements, drug-specific assays are not available in most hospital laboratories, but drug levels are needed in some urgent/emergency situations. This study describes the development of a qualitative screen for the presence of DOAC or fondaparinux using coagulation tests found in most laboratories.

METHODS

The DOAC screen is composed of a heparin anti-Xa activity assay and thrombin time (TT) assay. The STA®-Liquid-Anti-Xa assay calibrated with Stago Multi Hep® and STA®-TT were run on STA-R Max® analyzers. The anti-Xa activity and TT assays were repeated 5 times in samples of commercially available calibrators and controls for each drug: fondaparinux, dabigatran, rivaroxaban, apixaban, and edoxaban. Statistical analysis and correlations were performed for anti-Xa activity and TT results for each drug and pooled normal plasma.

RESULTS

A significant correlation was found between heparin-calibrated anti-Xa levels and fondaparinux, rivaroxaban, apixiban, and edoxaban (r2 = 0.99-1.0). Dabigatran showed a strong linear correlation (r2 = 0.99) with TT. Anti-Xa levels >0.3 IU/mL and TT >25 seconds were determined as cutoffs at our lab for the detection of clinically relevant drug levels of factor Xa inhibitor and direct thrombin inhibitor, respectively.

CONCLUSIONS

Our study demonstrates that commonly available heparin anti-Xa activity and TT assays can be used to qualitatively detect DOACs and fondaparinux and provides a method to establish a qualitative interpretation.

Case Report: Extended Duration Andexanet Alfa Infusion in a Surgical Trauma Patient

Background: Andexanet alfa (andexanet) is the only FDA-approved medication for reversal of apixaban and rivaroxaban anticoagulation for life-threatening or uncontrolled bleeding. Infusion modifications may be required in surgical patients undergoing prolonged operative intervention but have not previously been described. Case Report: A 78-year-old woman on rivaroxaban for atrial fibrillation was admitted to the trauma service for a mechanical fall, sustaining a T4 burst fracture with severe canal stenosis and spinal cord edema resulting in loss of strength and sensation in her legs. Clinically relevant rivaroxaban activity was verified with an elevated low molecular weight heparin anti-factor Xa assay, and laboratory confirmed coagulopathy was demonstrated by a prolonged prothrombin time, thromboelastography (TEG) R-time, and activated clotting time (ACT). The patient required urgent surgical intervention for spinal fixation. Given the expected prolonged duration of the procedure, standard dose andexanet was initiated with a prolonged infusion at half the standard rate during the operation. The procedure was successful and intraoperative TEGs demonstrated normalization of R-time and ACT throughout the procedure. The patient did not experience any complications postoperatively and successfully discharged to inpatient rehabilitation. Conclusion: Modifications to the andexanet infusion may be required in surgical patients requiring rivaroxaban reversal for a prolonged procedure. Further data are needed to determine the optimal approach to infusion modification.

Determination of Anti-Xa Inhibitor Plasma Concentrations Using a Universal Edoxaban Calibrator

A universal calibrator for the determination of all anti-Xa inhibitors would support laboratory processes. We aimed to test the clinical performance of an anti-Xa assay utilizing a universal edoxaban calibrator to determine clinically relevant concentrations of all anti-Xa inhibitors. Following a pilot study, we enrolled 553 consecutive patients taking rivaroxaban, edoxaban, or apixaban from nine study centers in a prospective cross-sectional study. The Technochrom^® anti-Xa assay was conducted using the Technoview^® edoxaban calibrator. Using ultra-high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS), anti-Xa inhibitor drug concentrations were determined. Sensitivities and specificities to detect three clinically relevant drug concentrations (30 µgL^-1, 50 µgL^-1, 100 µgL^-1) were determined. Overall, 300 patients treated with rivaroxaban, 221 with apixaban, and 32 with edoxaban were included. The overall correlation coefficient (r_s) was 0.95 (95% CI 0.94, 0.96). An area under the receiver operating characteristic curve of 0.96 for 30 µgL^-1, 0.98 for 50 µgL^-1, and 0.99 for 100 µgL^-1 was found. The sensitivities were 92.3% (95% CI 89.2, 94.6), 92.7% (89.4, 95.1), and 94.8% (91.1, 97.0), respectively (specificities 82.2%, 93.7%, and 94.4%). In conclusion, the clinical performance of a universal, edoxaban-calibrated anti-Xa assay was solid and most drug concentrations were predicted correctly.

The effect of contrast agents on the anticoagulant properties of oral factor Xa inhibitors

BACKGROUND

Contrast agents may affect the anticoagulant properties of novel oral anticoagulants.

PURPOSE

To evaluate the effect of iohexol as a contrast agent on the anticoagulant activity of oral factor Xa inhibitors.

MATERIAL AND METHODS

The study included 65 individuals who underwent contrast computed tomography(CT). Group 1 comprised 20 patients using rivaroxaban, Group 2, 20 patients using apixaban, and Group 3, 20 patients using edoxaban. Group 4 was the control group of five healthy volunteers. Iohexol (60 mL) was used as a contrast agent. Blood samples of 2 mL were withdrawn into two tubes at 4 h after the drug dose and 1 h after the contrast CT (CT was performed 3 h after the drug was taken) from all the patients, and for the control group, at any time before and 1 h after contrast CT. The anticoagulant properties of rivaroxaban, apixaban, and edoxaban were evaluated using anti-factor Xa levels.

RESULTS

The anti-factor Xa level was increased after using the contrast agent in the rivaroxaban group (0.66 ± 0.32 U/mL vs. 0.67 ± 0.32 U/mL; P = 0.01) and the edoxaban group (0.74 ± 0.35 U/mL vs. 0.76 ± 0.36 U/mL; P = 0.006). No significant difference was observed in the apixaban group (0.66 ± 0.33 U/mL vs. 0.66 ± 0.32 U/mL; P = 0.21) and control group (0.02 ± 0.01 U/mL vs. 0.03 ± 0.01 U/mL; P = 0.33).

CONCLUSION

The anticoagulant properties of rivaroxaban and edoxaban tended to increase significantly, but there was no statistically significant difference in the anticoagulant properties of apixaban after the administration of contrast agent. To determine whether the small laboratory difference has a clinical effect, there is a need for larger clinical trials (NCT04611386).

Rivaroxaban and apixaban are less effective than enoxaparin for the prevention of catheter-induced clotting in vitro

BACKGROUND

Central venous catheters are prone to clotting, particularly in patients with cancer. Although low-molecular-weight heparin and direct oral anticoagulants, such as apixaban and rivaroxaban, have been evaluated for the prevention of catheter thrombosis, their efficacy remains uncertain.

OBJECTIVES

Compare apixaban and rivaroxaban with enoxaparin for the prevention of catheter-induced clotting in vitro.

METHODS

To address this uncertainty, we used a well-established microplate-based assay to compare the effects of enoxaparin, apixaban, and rivaroxaban on catheter-induced thrombosis and thrombin generation in human plasma.

RESULTS

Consistent with our previous findings, catheter segments shortened the clotting time and promoted thrombin generation. When compared at concentrations with similar anti-factor Xa activity as enoxaparin, apixaban and rivaroxaban were >20-fold less potent than enoxaparin for the prevention of catheter-induced clotting and thrombin generation.

CONCLUSION

The prevention of catheter thrombosis in patients with cancer is challenging. Clinical trials are needed to compare the efficacy of low-molecular-weight heparin with that of direct oral anticoagulants both for the prevention and treatment of catheter thrombosis.

Comparison of Commercial Low Molecular Weight Heparin and Homemade Anti-Xa Calibrators to a Commercial Specific Anti-Xa Calibrator for Plasma Rivaroxaban Quantification by Anti-Xa Oral Anticoagulant Plasma Concentration Chromogenic Assay

Objective

The main concern about measuring the concentration of rivaroxaban by anti-Xa assay in some laboratories is the lack of a commercial specific calibrator in emergencies. Therefore, this study aimed at providing a homemade anti-Xa calibrator and commercial low molecular weight heparin (LMWH) anti-Xa calibrator.

Methods

The anti-Xa plasma concentration of rivaroxaban was measured in 70 patients using a commercial specific anti-Xa calibrator, a commercial LMWH anti-Xa calibrator, and a homemade anti-Xa calibrator.

Results

We demonstrated a significant correlation and agreement (P < .001) between LMWH-calibrated anti-Xa and the commercial specific calibrator. A significant correlation (P < .001) was found between homemade calibrated anti-Xa made by normal pooled plasma and that calibrated with a commercial specific drug. The nonspecific homemade and LMWH calibrators had excellent agreement (P < .001) and can be used interchangeably.

Conclusion

Our data showed that for estimating rivaroxaban concentrations, the LMWH calibrator could be used as an alternative calibrator in the anti-Xa assay.

The myths behind DOAC measurement: Analyses of prescribing information from different regulatory bodies and a call for harmonization

For more than a decade, US laboratories have failed to implement solutions to help their clinicians in managing complex situations or patients on direct oral anticoagulants (DOACs). The problem may find different origins, among which is the position of the Food and Drug Administration, which categorized these drugs as monitoring- and measurement-free, whereas other regulatory bodies like the European Medicines Agency or the Therapeutic Goods Administration in Australia were more conservative on the principle that the absence of proof (of monitoring/measurement benefits) is not proof of an absence (of monitoring/measurement needs). Pivotal clinical studies that led to the approval of DOACs were presented as devoid of such testing, although some companies considered monitoring as a solution to improve their benefit/risk ratio. In this JTH In Clinics issue, we report more than a decade of development that has permitted the activation of smart laboratory solutions to qualify or quantify DOACs and discuss myths and misconceptions around technical and regulatory requirements that support the current reluctance of implementing these technologies in most US laboratories. Use of DOACs is ever expanding, with DOAC prescriptions now exceeding those of other anticoagulants, including vitamin K antagonists, in some geographies. As this use increases, the likely need to measure DOAC exposure will also increase. Measurement of DOACs does not represent any technical difficulty. That these laboratory tests are not available in some locations suggests disparities in patient care, and we suggest it is time to address such inequalities.

Comparison of Managing Factor Xa Inhibitor to Unfractionated Heparin Transitions by aPTT Versus a Treatment Guideline Utilizing Heparin Anti-Xa Levels

BACKGROUND

There are inadequate data on the optimal strategy for transitioning factor Xa inhibitors (FXai; apixaban, rivaroxaban) to unfractionated heparin (UFH) infusions.

OBJECTIVE

In patients transitioning from an FXai to an UFH infusion, this study compared the safety and efficacy of monitoring UFH infusions using an activated partial thromboplastin time (aPTT) titration scale versus utilizing an UFH-calibrated anti-Xa titration scale aided by a novel institutional guideline.

METHODS

A retrospective cohort analysis was conducted on adult patients transitioning from an FXai to an UFH infusion at 2 medical centers from June 1, 2018, to November 1, 2020. One institution utilized aPTT while the other institution primarily used UFH-calibrated anti-Xa. The primary endpoint was a composite of death, major bleeding, or new thrombosis during the hospitalization with a planned noninferiority analysis. Secondary outcomes were also collected including the amount and duration of UFH administered between cohorts.

RESULTS

The incidence rate of the primary composite endpoint was 6.3% in the anti-Xa group and 11% in the aPTT group (P < 0.001 for noninferiority, P = 0.138 for superiority) meeting noninferiority criteria. No statistical differences were seen in new thrombosis, major bleeding, or any bleeding.

CONCLUSION AND RELEVANCE

This represents the first report of a comparison between aPTT versus anti-Xa monitoring in relation to clinical outcomes for patients transitioning from an FXai to an UFH infusion. A transition guideline primarily utilizing an UFH-calibrated anti-Xa assay appears to be a safe alternative to aPTT monitoring and can aid facilities in the management of patients during these complex transitions.

Accuracy of a Single, Heparin-Calibrated Anti-Xa Assay for the Measurement of Rivaroxaban, Apixaban, and Edoxaban Drug Concentrations: A Prospective Cross-Sectional Study

Background

Applying a single anti-Xa assay, calibrated to unfractionated heparin to measure rivaroxaban, apixaban, and edoxaban would simplify laboratory procedures and save healthcare costs.

Aim

We hypothesized that a heparin-calibrated anti-Xa assay would accurately measure rivaroxaban, apixaban, and edoxaban drug concentrations and correctly predict clinically relevant drug levels.

Methods

This analysis is part of the Simple-Xa study, a prospective multicenter cross-sectional study conducted in clinical practice. Patients treated with rivaroxaban, apixaban, or edoxaban were included. Anti-Xa activity was measured using the Siemens INNOVANCE^® Heparin assay. Drug concentrations were determined using ultra-high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Cut-off levels were determined in a derivation dataset (50% of patients) and sensitivities and specificities were calculated in a verification dataset (50% of patients).

Results

Overall, 845 patients were available for analysis. Correlation coefficients (r _s ) between the heparin-calibrated anti-Xa assay and drug concentrations were 0.97 (95% CI 0.97, 0.98) for rivaroxaban, 0.96 (0.96, 0.97) for apixaban, and 0.96 (0.94, 0.99) for edoxaban. The area under the receiver operating characteristics curve (ROC) was 0.99 for all clinically relevant drug concentrations. In the verification dataset, the sensitivity was 94.2% (95% CI 90.8-96.6) for 30 μg L^-1, 95.8% (92.4-98.0) for 50 μg L^-1, and 98.7% (95.5-99.9) for 100 μg L^-1. Specificities were 86.3% (79.2-91.7), 89.8% (84.5-93.7), and 88.7% (84.2-92.2), respectively.

Conclusion

In a large prospective study in clinical practice, a strong correlation of heparin-calibrated anti-Xa measurements with LC-MS/MS results was observed and clinically relevant drug concentrations were predicted correctly.

DOAC Dipstick testing can reliably exclude the presence of clinically relevant DOAC concentrations in circulation

In certain clinical situations, it is necessary to determine whether clinically relevant plasma levels of direct oral anticoagulants (DOACs) are present. We examined whether qualitative testing of DOACs in urine samples can exclude DOAC plasma concentrations of ≥30 ng/mL. This prospective single-center cohort study included consecutive patients treated with an oral direct factor Xa inhibitor (DXI) (apixaban, n  = 31, rivaroxaban, n  = 53) and direct thrombin inhibitor (DTI) (dabigatran, n  = 44). We aimed to define the negative predictive value (NPV) and other statistical parameters of detecting DXIs and DTIs by DOAC Dipstick at plasma concentrations of ≥30 ng/mL. We also determined the best-fit threshold plasma levels using chromogenic substrate assays by logistic regression analysis. Between July 2020 and July 2021, 128 eligible patients (mean age 66 years, 55 females) were included into the study. The NPVs and sensitivities for DXI and DTI of DOAC Dipstick were 100% at ≥30 ng/mL plasma, for specificities 6 and 21% and for positive predictive values 62 and 72%, respectively. All diagnostic statistical tests improved to values between 86 and 100% at best-fitting plasma thresholds of ≥14 ng/mL for DXI and ≥19 ng/mL for DTI. Visual analysis using the DOAC Dipstick was 100% in agreement with that of the optoelectronic DOASENSE Reader for all the three DOACs.

DOAC Dipstick testing can reliably exclude the presence of DOACs in urine samples at best-fitting thresholds of >14 and >19 ng/mL in plasma. The performance of the DOAC Dipstick at detecting lower DOAC concentrations in plasma requires confirmation.

Utilization of apixaban anti-Xa levels in transition from apixaban to warfarin in a patient with chronic renal dysfunction

DISCLAIMER

In an effort to expedite the publication of articles related to the COVID-19 pandemic, AJHP is posting these manuscripts online as soon as possible after acceptance. Accepted manuscripts have been peer-reviewed and copyedited, but are posted online before technical formatting and author proofing. These manuscripts are not the final version of record and will be replaced with the final article (formatted per AJHP style and proofed by the authors) at a later time.

PURPOSE

The effect of apixaban on anti-factor Xa (anti-Xa) assays and international normalized ratio (INR) complicates transitions between anticoagulant agents. When switching from apixaban to warfarin, the recommendation is to begin both a parenteral anticoagulant and warfarin at the time of the next apixaban dose and to discontinue the parenteral agent when INR is in an acceptable range. This proves challenging in renal dysfunction, as continued presence of apixaban contributes to both a prolonged effect on the INR and continued therapeutic levels of anticoagulation.

SUMMARY

This case describes the transition of apixaban to warfarin in a patient with acute on chronic kidney disease and recent deep vein thrombosis, utilizing chromogenic apixaban anti-Xa assays to assess the level of anticoagulation and avoid unnecessary parenteral anticoagulation.

CONCLUSION

Utilization of apixaban anti-Xa levels aided in the transition from apixaban to warfarin in a patient with chronic renal failure and avoided need for parenteral bridging therapy.

Prevalence and predictors of left atrial thrombosis in atrial fibrillation patients treated with non-vitamin K antagonist oral anticoagulants

BACKGROUND

Few data are available regarding the prevalence of left atrium (LA) thrombi in atrial fibrillation (AF) patients treated with non-vitamin K antagonist oral anticoagulants (NOACs). Methods: We evaluated the prevalence and predictors of LA/LA appendage (LAA) thrombi in non-valvular AF patients treated with NOACs referring to a single centre for a scheduled electrical cardioversion (ECV) or catheter ablation (CA). Transesophageal echocardiography (TEE) was performed within 12 h prior to the index procedure.

RESULTS

A total of 352 consecutive patients with non-valvular AF treated with NOACs were included in this analysis (ECV group n = 176 and CA group n = 176) between 2013 and 2018. 85 patients (24.2%) were on dabigatran, 150 (42.7%) on rivaroxaban, 104 (29.6%) on apixaban and 13 (3.7%) on edoxaban. A LA/LAA thrombus was detected by TEE in 27 (7.7%) patients, 18 in the ECV group and nine in the ablation group; 18 (5.1%) patients presented dense LA/LAA spontaneous echo contrast (SEC). Predictors of LA/LAA thrombi were a CHA₂DS₂-VASc score > 3 (OR 4.54, 95% CI 1.50 - 13.70, p value = .007) and obesity (OR 6.01, 95% CI 1.95 - 18.50, p value = .001).

CONCLUSIONS

Among real-world patients with non-valvular AF treated with NOACs, we found a high incidence of LA/LAA thrombi compared to previous reports. The main predictors of LA/LAA thrombosis were a CHA₂DS₂-VASc score > 3 and obesity.

Target Drug-Calibrated Anti-Xa Activity Assays and Expected Peak-Trough Levels in an Asian Population: A Multicenter Study

BACKGROUND

For patients taking factor Xa (FXa) inhibitors who have life-threatening bleeding, emergency surgery, drug interactions, etc., a rapid and precise assay is needed to monitor for potential medication failure, to assess safety during periprocedural anticoagulation management, and to manage the care of chronically anticoagulated patients. Anti-factor Xa (anti-Xa) activity assays have been recommended in guidelines, but the evaluation of different calibrations of anti-Xa activity assays and the data on the recommended range are still limited, especially in the Asian population.

METHODS

This is a nationwide multicenter methodology exploratory study in an Asian population, including nine hospitals from Beijing, Shanghai, Liaoning, Shandong, Jiangsu, Anhui, Henan, Chongqing, and Fujian. A total of 485 healthy volunteers and 219 patients taking rivaroxaban or apixaban (single dose) were enrolled in the study. High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS) was employed to detect plasma rivaroxaban and apixaban. The prothrombin time (PT), activated partial thromboplastin time (APTT), and levels of anti-Xa activity were tested as pharmacodynamic parameters in plasma samples. We evaluated the correlation of anti-Xa activity and blood concentration via HPLC-MS, and then compared the two methods of target drug-calibrated and low-molecular-weight heparin (LMWH)-antithrombin-calibrated anti-Xa activity. Correlations between variables were examined using Pearson's correlation analysis. Logistic regression was applied to evaluate significant differences in anti-Xa activity and blood concentration, using models adjusted by baseline characteristics.

RESULTS

The results suggested anti-Xa activity had better correlation with blood concentrations of apixaban and rivaroxaban than APTT and PT (p < 0.001). Target drug-calibrated anti-Xa activity had better correlation with HPLC-MS results at every dose level and blood collection time (p < 0.001). The expected concentrations (ng/mL) derived from rivaroxaban-calibrated assays of rivaroxaban 10 mg, 15 mg, and 20 mg were about 210, 330, and 270 at peak concentrations, and 28, 44, and 58, respectively, at the trough concentrations.

CONCLUSIONS

In this study, we confirm that target drug calibration of anti-Xa activity is a better quantitative detection method for oral direct FXa inhibitors than LMWH-calibrated anti-Xa activity in clinical practice, and expected peak-trough levels are recommended for the Asian population.

Difficulties Detecting Clinically Relevant Factor Xa Inhibitor Levels Prior to Reversal With Andexanet Alfa for Intracranial Hemorrhage

Coagulation factor Xa (recombinant), inactivated-zhzo (andexanet alfa) is approved for reversal of life-threatening bleeding with rivaroxaban and apixaban use. Clinical decision-making to initiate reversal is reliant on dose taken and timing of last dose. In practice, timing of last dose may be unknown, and the turnaround time for drug-specific anti-factor Xa levels at some institutions may be prolonged, leaving clinicians balancing a difficult decision with limited tools. This report includes a series of 3 patients who presented to our institution with an intracranial hemorrhage and received andexanet alfa for apixaban reversal. These cases highlight the challenges clinicians are facing when using andexanet alfa for emergent rivaroxaban or apixaban reversal when the timing of last dose is unknown, or patients fall outside of the recommended timeframe for use and clinically relevant drug levels are still suspected. Based on our experiences, we encourage other institutions to evaluate their abilities to rapidly and accurately detect the presence of clinically relevant rivaroxaban and apixaban levels when utilizing andexanet alfa.

Using a low-molecular weight heparin-calibrated anti-factor Xa assay to assess the concentration of apixaban and rivaroxaban

INTRODUCTION

Direct oral anticoagulant (DOAC)-inhibiting factor Xa (FXa-DOAC) are being increasingly used as prophylaxis of venous thromboembolism and for prevention of stroke in patients with atrial fibrillation. In contrast to vitamin K antagonists, DOACs do not require monitoring in general. However, it is sometimes of value in the acute setting, for instance when considering a reversal agent in uncontrolled bleeding in patients on DOAC.

METHODS

We evaluated if a low-molecular weight heparin (LMWH)-calibrated anti-factor Xa assay could be used to estimate FXa-DOAC concentration in the concentration range <100 ng/mL by spiking known concentrations of FXa-DOAC and from those result calculate the FXa-DOAC concentration from the response of the LMWH assay. This procedure was then evaluated by comparing the result with a drug-calibrated chromogenic assay and liquid chromatography tandem mass spectrometry (LC-MS/MS) on clinical plasma samples from patients treated with apixaban or rivaroxaban.

RESULTS

Although the measuring range was narrower for the LMWH-calibrated assay, concentrations recalculated from the LMWH assay was comparable with those measured by the drug-calibrated method when compared with LC-MS/MS.

CONCLUSION

We suggest that an LMWH-calibrated anti-factor Xa assay can be used after characterization of the response of FXa-DOACs to give guidance on the concentration of apixaban and rivaroxaban. Shorter turnaround time than LC-MS/MS and the greater availability than drug-calibrated chromogenic assays could make this a valuable option in the acute setting.

The Evaluation of Hemostatic Abnormalities Using a CWA-Small Amount Tissue Factor Induced FIX Activation Assay in Major Orthopedic Surgery Patients

We analyzed the utility for a clot waveform analysis (CWA) of small tissue factor induced FIX activation (sTF/FIXa) assay in patients with major orthopedic surgery (including total hip arthroplasty [THA] and total knee arthroplasty [TKA]) receiving edoxaban for the prevention of venous thromboembolism (VTE). The sTF/FIXa assay using recombinant human TF in platelet-rich plasma (PRP) and platelet-poor plasma (PPP) was performed using a CWA in the above patients to monitor the efficacy of edoxaban administration. Of 147 patients (109 THA and 38 TKA), 21 exhibited deep vein thrombosis (DVT), and 15 had massive bleeding. Increased peak heights of the CWA-sTF/FIX were observed in almost patients after surgery and prolonged peak heights of the CWA-sTF/FIX were observed in almost patients treated with edoxaban. The peak heights and times of the CWA-sTF/FIX were significantly higher and shorter, respectively, in PRP than in PPP. There were no significant differences in parameters of the CWA-sTF/FIXa between the patients with and without DVT or between those with and without massive bleeding. The peak time of CWA-sTF/FIXa were significantly longer in TKA patients than in THA patients on day 1 after surgery. The second derivative peak height of the CWA-sTF/FIXa was significantly lower in TKA patients than in THA patients on day 4. The CWA-sTF/FIX reflected hemostatic abnormalities after surgery and the administration of edoxaban, and the results were better in PRP than PPP. Further studies separately analyzing the THA and TKA subgroups should be conducted.

A universal anti-Xa assay for rivaroxaban, apixaban, and edoxaban measurements: method validation, diagnostic accuracy and external validation

A universal anti‐Xa assay for the determination of rivaroxaban, apixaban and edoxaban drug concentrations would simplify laboratory procedures and facilitate widespread implementation. Following two pilot studies analysing spiked samples and material from 698 patients, we conducted a prospective multicentre cross‐sectional study, including 867 patients treated with rivaroxaban, apixaban or edoxaban in clinical practice to comprehensively evaluate a simple, readily available anti‐Xa assay that would accurately measure drug concentrations and correctly predict relevant levels in clinical practice. Anti‐Xa activity was measured by an assay calibrated with low‐molecular‐weight heparin (LMWH) in addition to ultra‐high performance liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). As an external validation, LMWH‐calibrated anti‐Xa activity was also determined in nine external laboratories. The LMWH‐calibrated anti‐Xa activity correlated strongly with rivaroxaban, apixaban or edoxaban drug levels [r_s = 0·98, 95% confidence interval (CI) 0·98–0·98]. The sensitivity for the clinically relevant cut‐off levels of 30, 50 and 100 µg/l was 96·2% (95% CI 94·4–97·4), 96·4% (95% CI 94·4–97·7) and 96·7% (95% CI 94·3–98·1) respectively. Concordant results were obtained in the external validation study. In conclusion, a universal, LMWH‐calibrated anti‐Xa assay accurately measured rivaroxaban, apixaban and edoxaban concentrations and correctly predicted relevant drug concentrations in clinical practice.

Evaluation of Anti-Xa Apixaban and Rivaroxaban Levels With Respect to Known Doses in Relation to Major Bleeding Events

BACKGROUND

Although not routinely recommended, anti-Xa level monitoring for apixaban or rivaroxaban may be useful in certain clinical scenarios. There are currently no laboratory standards, therapeutic ranges, or proven correlation between anti-Xa levels and clinical outcomes.

OBJECTIVE

This study describes the utilization, application, and association of anti-Xa levels with clinical outcomes in patients receiving apixaban or rivaroxaban.

METHODS

This retrospective, descriptive study included adult inpatients within the Houston Methodist System on apixaban or rivaroxaban with at least one anti-Xa level ordered subsequent to administered doses. The primary endpoint was major bleeding according to International Society on Thrombosis and Haemostasis criteria. Secondary endpoints included reasons for anti-Xa level ordering, anti-Xa levels at different time intervals post-dose, and thrombotic events. Pre-specified subgroup analyses were performed to further evaluate the primary endpoint.

RESULTS

The study population consisted of 169 patients and 234 anti-Xa levels. Twenty-nine levels were obtained in context of major bleeding. The majority of levels were not drawn as peak levels 2-4 hours post-dose, however remained quantifiable above typical observed levels within this timeframe and well beyond 24 hours post-dose. Patient characteristics with major bleeding included elderly age, acute renal impairment, and low body weight. At least 14 unique reasons for anti-Xa level ordering were identified. Twenty-nine levels were associated with thrombotic events.

CONCLUSION

Anti-Xa levels may be useful for assessment of current drug concentrations, immediate safety of therapy, and guidance for possible clinical interventions. Dose titration and reversal therapies based on anti-Xa level results in major bleeding warrant further research.

Heparin Anti-Xa Activity, a Readily Available Unique Test to Quantify Apixaban, Rivaroxaban, Fondaparinux, and Danaparoid Levels

BACKGROUND

Despite their usefulness in perioperative and acute care settings, factor-Xa inhibitor-specific assays are scarcely available, contrary to heparin anti-Xa assay. We assessed whether the heparin anti-Xa assay can (1) be used as a screening test to rule out apixaban, rivaroxaban, fondaparinux, and danaparoid levels that contraindicate invasive procedures according to current guidelines (>30 ng·mL-1, >30 ng·mL-1, >0.1 µg·mL-1, and >0.1 IU·mL-1, respectively), (2) quantify the anticoagulant level if found significant, that is, if it exceeded the abovementioned threshold.

METHODS

In the derivation cohort then in the validation cohort, via receiver operating characteristics (ROC) curve analysis, we evaluated the ability of heparin anti-Xa assay to detect levels of factor-Xa inhibitors above or below the abovementioned safety thresholds recommended for an invasive procedure (screening test). Among samples with relevant levels of factor-Xa inhibitor, we determined the conversion factor linking the measured level and heparin anti-Xa activity in a derivation cohort. In a validation cohort, the estimated level of each factor-Xa inhibitor was thus inferred from heparin anti-Xa activity. The agreement between measured and estimated levels of factor-Xa inhibitors was assessed.

RESULTS

Among 989 (355 patients) and 756 blood samples (420 patients) in the derivation and validation cohort, there was a strong linear relationship between heparin anti-Xa activities and factor-Xa inhibitors measured level (r = 0.99 [95% confidence interval {CI}, 0.99-0.99]). In the derivation cohort, heparin anti-Xa activity ≤0.2, ≤0.3, <0.1, <0.1 IU·mL-1 reliably ruled out a relevant level of apixaban, rivaroxaban, fondaparinux, and danaparoid, respectively (area under the ROC curve ≥0.99). In the validation cohort, these cutoffs yielded excellent classification accuracy (≥96%). If this screening test indicated relevant level of factor-Xa inhibitor, estimated and measured levels closely agreed (Lin's correlation coefficient close to its maximal value: 95% CI, 0.99-0.99). More than 96% of the estimated levels fell into the predefined range of acceptability (ie, 80%-120% of the measured level).

CONCLUSIONS

A unique simple test already widely used to assay heparin was also useful for quantifying these 4 other anticoagulants. Both clinical and economic impacts of these findings should be assessed in a specific study.

A Systemwide Approach for Navigating the Dilemma of Oral Factor Xa Inhibitor Interference With Unfractionated Heparin Anti-Factor Xa Concentrations

BACKGROUND

Oral factor Xa inhibitors are known to significantly increase heparin anti-Xa concentrations, which leads to inaccuracies when monitoring intravenous unfractionated heparin (IV UFH). Guidance for managing this laboratory interference is lacking, creating substantial uncertainty in clinical practice.

OBJECTIVE

To describe a strategy used by a large academic institution for managing the controversy of laboratory interference in the setting of oral factor Xa inhibitor use and provide effectiveness and safety data for this approach.

METHODS

In December 2016, a new Heparin IV Direct Oral Anticoagulant (DOAC) Interference PowerPlan (a comprehensive order set) was made available in the electronic health record (Cerner, North Kansas City, MO) throughout the health system. We retrospectively examined 169 patients with events reported in the error reporting system, RISKMASTER, and evaluated reports with and without the use of the PowerPlan. Effectiveness was determined through evaluation of thrombosis. The Naranjo criteria for causality were applied to assess thrombotic events.

RESULTS

Of 56 events that were reported with apixaban when the PowerPlan was not ordered, 4 (7%) thrombotic events occurred within 7 days of UFH initiation. One out of the 4 events (25%) that occurred when the PowerPlan was not appropriately initiated was considered probable using the Naranjo Scale. Three additional events (75%) were possible using the Naranjo Scale.

CONCLUSION AND RELEVANCE

The Heparin IV DOAC Interference PowerPlan appears to be conducive to positive patient outcomes when evaluating voluntary reported events and may assist clinicians with managing the therapeutic dilemma of this laboratory interference.

Electrophysiological effects of non-vitamin K antagonist oral anticoagulants on atrial repolarizing potassium channels

AIMS

Non-vitamin K antagonist oral anticoagulants (NOACs) are widely used in the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation (AF). The efficacy of NOACs has been attributed in part to pleiotropic effects that are mediated through effects on thrombin, factor Xa, and their respective receptors. Direct pharmacological effects of NOACs and cardiac ion channels have not been addressed to date. We hypothesized that the favourable clinical outcome of NOAC use may be associated with previously unrecognized effects on atrial repolarizing potassium channels.

METHODS AND RESULTS

This study was designed to elucidate acute pharmacological effects of NOACs on cloned ion channels Kv11.1, Kv1.5, Kv4.3, Kir2.1, Kir2.2, and K2P2.1 contributing to IKr, IKur, Ito, IK1, and IK2P K+ currents. Human genes, KCNH2, KCNA5, KCND3, KCNJ2, KCNJ12, and KCNK2, were heterologously expressed in Xenopus laevis oocytes, and currents were recorded using voltage-clamp electrophysiology. Apixaban, dabigatran, edoxaban, and rivaroxaban applied at 1 µM did not significantly affect peak current amplitudes of Kv11.1, Kv1.5, Kv4.3, Kir2.1, Kir2.2, or K2P2.1 K+ channels. Furthermore, biophysical characterization did not reveal significant effects of NOACs on current-voltage relationships of study channels.

CONCLUSION

Apixaban, dabigatran, edoxaban, and rivaroxaban did not exhibit direct functional interactions with human atrial K+ channels underlying IKr, IKur, Ito, IK1, and IK2P currents that could account for beneficial clinical outcome associated with the drugs. Indirect or chronic effects and potential underlying signalling mechanisms remain to be investigated.

Transitioning hospitalized patients from rivaroxaban or apixaban to a continuous unfractionated heparin infusion: A retrospective review

PURPOSE

To determine a patient's clinical course based on the use of an activated partial thromboplastin time (aPTT) or heparin anti-Xa assay when transitioning from rivaroxaban or apixaban to an unfractionated heparin infusion.

METHODS

A retrospective chart review was conducted to investigate how unfractionated heparin infusions were managed at a tertiary care hospital in the setting of recent apixaban or rivaroxaban administration. Patients were separated into 2 cohorts based on the chosen heparin infusion monitoring assay: heparin anti-Xa or aPTT. The primary composite outcome was total number of bleeding and thrombotic events; the secondary composite outcome was average incidence of heparin infusion holds and rate changes per patient.

RESULTS

Data were collected from 76 patients (heparin anti-Xa = 69, aPTT = 7). Due to the limited number of patients within the aPTT cohort, this data was excluded from the analysis, and heparin anti-Xa descriptive statistics were reported without statistical comparisons. In the heparin anti-Xa group, a total of 10 bleeds and 1 thrombus were discovered. Additionally, the average number of infusion holds and rate changes was 0.841 and 2.65 times per patient, respectively, for those patients monitored via heparin anti-Xa assay.

CONCLUSION

In the presence of a recently administered oral anti-Xa anticoagulant, more down-titrations occurred in the initial 6 hours of the heparin infusion when measuring anti-Xa activity, and most up-titrations occurred after 36 hours. Baseline heparin anti-Xa activity may be a useful tool to identify patients with residual plasma concentrations of apixaban and rivaroxaban to help better individualize heparin therapy.

The Relationship between the Initial Anti-factor Xa Measurement and the Duration of Direct Oral Anticoagulant Influence in Patients Transitioning to Heparin

BACKGROUND

Anticoagulation monitoring during transition from direct oral anticoagulants (DOAC) to heparin infusions is a significant challenge. Factor Xa inhibitors influence the heparin calibrated antifactor Xa assay. The University of Virginia (UVA) Medical Center utilized a corrected antifactor Xa assay (c-AXA) during this transition period, which removes DOAC-mediated antifactor Xa activity (d-AXA) and reflects heparin-specific activity. Currently, the duration of this influence is not well described.

STUDY OBJECTIVE

This study had two aims: to determine if the initial d-AXA is predictive of the duration of DOAC influence and to further characterize this influence among different patient populations.

METHODS

This retrospective study included adult patients admitted to UVA Medical Center between September 2016 and March 2017, with c-AXA measurements, who received apixaban or rivaroxaban within 48 hours before heparin initiation. A Pearson correlation test, Kaplan-Meier Survival Analysis, and multivariate linear regression were used to assess the relationship between initial d-AXA and duration of influence.

RESULTS

Sixty-eight patients met inclusion criteria and were maintained on either apixaban (85%) or rivaroxaban (15%) before heparin initiation. The initial d-AXA ranged from 0.11 to 3.27 IU/ml. The mean duration of influence was 69.3 ± 46.2 hours, with a median duration of 62.7 hours. No strong correlation was identified between initial d-AXA and duration of influence (R² = 0.124). Presence of interacting medications significantly increased duration of influence (p=0.012). No significant difference in duration of influence existed between patients with normal renal function and those with dynamic renal function (p=0.84), or with body mass index (BMI) greater than 40 kg/m² (p=0.16).

CONCLUSIONS

The initial d-AXA was not predictive of duration of influence in patients transitioning from DOACs to heparin infusion; however, the median duration of influence suggests influence may be present for longer than currently stated in the literature, especially in those taking interacting medications.

Chromogenic anti-FXa assay calibrated with low molecular weight heparin in patients treated with rivaroxaban and apixaban: possibilities and limitations

Introduction

Clinical application of rivaroxaban and apixaban does not require therapeutic monitoring. Commercial anti-activated factor X (anti-FXa) inhibition methods for all anti-FXa drugs are based on the same principle, so there are attempts to evaluate potential clinical application of heparin-calibrated anti-FXa assay as an alternative method for direct FXa inhibitors. We aimed to evaluate relationship between anti-FXa methods calibrated with low molecular weight heparin (LMWH) and with drug specific calibrators, and to determine whether commercial LMWH anti-FXa assay can be used to exclude the presence of clinically relevant concentrations of rivaroxaban and apixaban.

Materials and methods

Low molecular weight heparin calibrated reagent (Siemens Healthineers, Marburg, Germany) was used for anti-FXa activity measurement. Innovance heparin (Siemens Healthineers, Marburg, Germany) calibrated with rivaroxaban and apixaban calibrators (Hyphen BioMed, Neuville-sur-Oise, France) was used for quantitative determination of FXa inhibitors.

Results

Analysis showed good agreement between LMWH calibrated and rivaroxaban calibrated activity (κ = 0.76) and very good agreement with apixaban calibrated anti-Xa activity (κ = 0.82), respectively. Low molecular weight heparin anti-FXa activity cut-off values of 0.05 IU/mL and 0.1 IU/mL are suitable for excluding the presence of clinically relevant concentrations (< 30 ng/mL) of rivaroxaban and apixaban, respectively. Concentrations above 300 ng/mL exceeded upper measurement range for LMWH anti-FXa assay and cannot be determined by this method.

Conclusion

Low molecular weight heparin anti-FXa assay can be used in emergency clinical conditions for ruling out the presence of clinically relevant concentrations of rivaroxaban and apixaban. However, use of LMWH anti-FXa assay is not appropriate for their quantitative determination as an interchangeable method.

Effect of low and moderate dose FEIBA to reverse major bleeding in patients on direct oral anticoagulants

OBJECTIVE

Management of acute, major or life threatening bleeding in the presence of direct acting oral anticoagulants (DOAC) is unclear. In the absence of a specific antidote, or in situations where there is a need for adjunctive therapy, the ideal prothrombin complex concentrate and dose is unclear. The goal of our study was to evaluate the outcomes of our reduced dosing strategy with FEIBA in patients experiencing a DOAC-related bleeding event.

DESIGN

Retrospective analysis of patients treated with FEIBA for a DOAC-related bleeding event.

SETTING

Academic medical center PATIENTS: Consecutive patients between May 2011 and April 2017 receiving FEIBA for a DOAC-related bleed INTERVENTIONS: None MEASUREMENTS & MAIN RESULTS: Of the 64 patients included in this analysis, 38 patients received low dose FEIBA (mean 10.0 ± 3.6 units/kg) and 26 received moderate dose (mean 24.3 ± 2.1 units/kg) FEIBA; an additional dose was requested in 6 patients. Six dabigatran patients received idarucizumab. 30 day event rates included 5 thromboembolic events (8%) and 9 (14%) patients expired. Follow-up CT-imaging for ICH, endoscopy/colonoscopy, or interventional radiology exams did not reveal any clinically concerning active bleeding or hematoma expansion except in 2 ICH patients with slight expansion between imaging sessions.

CONCLUSIONS

Low (<20 units/kg) to moderate (20-30 units/kg) doses of FEIBA, with the option for a repeat dose, may be an effective management strategy for obtaining hemostasis in DOAC-related major bleeding events.

Anti-Xa Oral Anticoagulant Plasma Concentration Assay in Real Life: Rivaroxaban and Apixaban Quantification in Emergency With LMWH Calibrator

BACKGROUND

Oral anti-Xa inhibitors have demonstrated noninferiority to vitamin K antagonists (VKAs) for the prevention of stroke in patients with atrial fibrillation and recurrent venous thromboembolism. They are associated with a decrease in major bleeding. In contrast with VKA, no coagulation monitoring is required. However, in clinical practice, determination of drug concentration is sometimes necessary.

OBJECTIVE

The objective of this study was to evaluate a low-molecular-weight heparin (LMWH) calibrated anti-Xa assay for the quantification of rivaroxaban and apixaban plasma concentration in emergency.

METHODS

The anti-Xa plasma concentration of rivaroxaban and apixaban were measured in emergency in 210 patients using STA anti-Xa liquid assay. For each plasma concentration <150 ng/mL of rivaroxaban or apixaban, an anti-Xa assay calibrated with LMWH was performed.

RESULTS

We demonstrated a significant correlation between LMWH anti-Xa activity and rivaroxaban ( R² = 0.947) or apixaban ( R² = 0.959) concentration and a significant correlation between rivaroxaban and apixaban plasma concentration ( R² = 0.972). A LMWH anti-Xa activity <0.50 IU/mL could exclude a plasma concentration of rivaroxaban and apixaban >30 ng/mL and indicate the feasibility of invasive procedure. Conclusion and Relevance: In the absence of a specific test, LMWH-calibrated anti-Xa assay could be used to determine the presence and evaluate the plasma concentration of oral anti-Xa inhibitors. However, these initial findings require confirmation using other chromogenic calibrated oral anti-Xa assays.

Anti-factor Xa Monitoring and Activated Charcoal for a Pediatric Patient With Rivaroxaban Overdose

Rivaroxaban, an oral anticoagulant, directly inhibits factor Xa (FXa). A 35-month-old boy was brought to the emergency department 15 minutes after ingesting 200 mg of rivaroxaban (16 mg/kg). Activated charcoal (AC) was administered; the patient was observed with monitoring of plasma anti-FXa levels and discharged the following day after an uneventful hospital observation. We identified two case series and seven case reports of potentially toxic rivaroxaban ingestion in the literature. No serious adverse effects were reported. The present case is the first reported use of anti-FXa monitoring after rivaroxaban ingestion. The magnitude of the effect of AC administration in this patient is unclear.

Managing transitions from oral factor Xa inhibitors to unfractionated heparin infusions

PURPOSE

Published evidence regarding the effects of oral factor Xa inhibitors on anticoagulation monitoring tests is reviewed with a focus on monitoring concerns that can arise during transitions to i.v. heparin therapy.

SUMMARY

Assays that measure inhibition of factor Xa activity (i.e., anti-Xa assays) are widely used in U.S. institutions to monitor i.v. heparin therapy and, in some cases, for monitoring other types of anticoagulation therapy. Clinicians have raised concerns that the use of anti-Xa assays to monitor heparin levels in hospitalized patients who must be transitioned from oral factor Xa inhibitor therapy to i.v. unfractionated heparin (UFH) infusions could yield unquantifiable or inaccurate results, leading to unnecessary UFH dose reductions and potential treatment failures; the manufacturer labeling of oral factor Xa inhibitors (apixaban, edoxaban, and rivaroxaban) does not provide specific guidance on this issue. Results of a literature review indicated that residual effects of oral factor Xa inhibitor use can result in substantial interference with the currently available chromogenic anti-Xa assays but negligible to moderate effects on global coagulation assays, which measure activated partial thromboplastin time (aPTT) or prothrombin time. Therefore, during the transition from an oral factor Xa inhibitor to i.v. UFH therapy, it may be prudent to consider an aPTT assay for anticoagulation monitoring.

CONCLUSION

The use of oral factor Xa inhibitors appears to affect the accuracy of anti-Xa assay results, with results of global coagulation assays affected to a lesser degree.

Thrombodynamics, a new global coagulation test: Measurement of heparin efficiency

The actual coagulation status may be reliably measured using only highly sensitive global functional tests; however, they are not numerous and all of them have disadvantages. Thrombodynamics (TD), a novel global coagulation test, is sensitive to hypo- and hypercoagulable states. The main properties of this test were investigated, and its capabilities for hemostasis analysis were verified through pharmacodynamic monitoring of the most widely used anticoagulants, heparins. The anticoagulant effects in the plasma of donors (n = 20) and patients after hip replacement (n = 20) spiked with unfractionated heparin or enoxaparin were measured in vitro to eliminate the influence of pharmacokinetic factors. Sensitivity for heparins was compared for activated partial thromboplastin time, thrombin generation tests and TD. TD was shown to reliably characterize the pharmacodynamics of any heparin in the entire range of its prophylactic and therapeutic concentrations. Inter-individual variability for the anticoagulant action of heparins was also calculated using the TD data. This variability did not differ between the investigated groups and did not exceed 12% and 20% for the stationary clot growth rate in the presence of unfractionated heparin and enoxaparin, respectively. That finding was in accordance with the values determined earlier using the thrombin generation test. The study results showed that TD has advantages over the other global methods of coagulation analysis. These advantages are good standardization, high reproducibility, independence of the parameter values from patient age and gender, and a narrower parameter distribution in a normal population. These results indicate that TD is a promising universal assessment method that improves the quality of hemostasis analysis because it more reliably detects deviations from the parameters' reference values.

Comparison of three different anti-Xa assays in major orthopedic surgery patients treated with direct oral anticoagulant

Background

Measurement of edoxaban plasma concentration has been gathering attention in major orthopedic surgery patients receiving edoxaban for the prevention of venous thromboembolism (VTE).

Methods

The anti-Xa activity was measured one hour after edoxaban intake using 3 different assays in 200 patients after major orthopedic surgery.

Results

The anti-Xa activities on Day 8 were significantly higher than those on Day 4 and those on Day 4 were significantly higher than those on Day 1. The anti-Xa activities in two assays closely correlated with each other, but the other anti-Xa assay did not correlated with other two assays. The anti-Xa activities as detected in the three Xa assays were significantly higher in the patients without deep vein thrombosis (DVT) than in those with DVT on Day 4. Additionally, there were no significant differences in the anti-Xa activities of assays A, B and C between patients with and without massive bleeding (MB) on Days 1, 4, 8 and 15.

Conclusion

The results of this study suggest that anti-Xa level could be predictive of the risk of VTE, but not of the risk of massive bleeding.

Monitoring of hemostatic abnormalities in major orthopedic surgery patients treated with edoxaban by APTT waveform

INTRODUCTION

An analysis of the activated partial thromboplastin time (APTT) in major orthopedic surgery patients receiving edoxaban for the prevention of venous thromboembolism (VTE) was carried out.

METHODS

The APTT waveform was analyzed in the above patients to monitor edoxaban administration.

RESULTS

Of these 99 patients, 12 exhibited deep vein thrombosis, and 25 had massive bleeding. An increased biphasic pattern of the APTT waveform was observed after the administration of edoxaban, but there were no significant differences between the patients with and without complications. The peak times of acceleration, velocity, and 1/2 fibrin formation were significantly prolonged after the administration of edoxaban, especially in patients with massive bleeding, and were moderately correlated with the anti-Xa activity. While the heights of velocity and acceleration peak 2 were lower in patients receiving warfarin treatment than in those receiving edoxaban, the widths of these parameters were significantly longer. The height of 1/2 fibrin formation and the width of acceleration peaks 1 and 2 and the velocity were significantly increased after the administration of edoxaban.

CONCLUSION

The peak time of the APTT waveform was significantly prolonged after the administration of edoxaban. The analysis of the APTT waveform may therefore be useful for the prediction of the risk of massive bleeding.

Accuracy and consistency of anti-Xa activity measurement for determination of rivaroxaban plasma levels

Essentials Accurate determination of anticoagulant plasma concentration is important in clinical practice. We studied the accuracy and consistency of anti-Xa assays for rivaroxaban in a multicentre study. In a range between 50 and 200 μg L-1 , anti-Xa activity correlated well with plasma concentrations. The clinical value might be limited by overestimation and intra- and inter-individual variation.

SUMMARY

Background Determining the plasma level of direct oral anticoagulants reliably is important in the work-up of complex clinical situations. Objectives To study the accuracy and consistency of anti-Xa assays for rivaroxaban plasma concentration in a prospective, multicenter evaluation study employing different reagents and analytical platforms. Methods Rivaroxaban 20 mg was administered once daily to 20 healthy volunteers and blood samples were taken at peak and trough levels (clinicaltrials.gov NCT01710267). Anti-Xa activity was determined in 10 major laboratories using different reagents and analyzers; corresponding rivaroxaban plasma concentrations were measured by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS). Findings Overall Pearson's correlation coefficient of anti-Xa levels and HPLC-MS results was 0.99 for Biophen® Heparin (95% CI, 0.99, 0.99), Biophen® DiXaI (95% CI, 0.99, 0.99) and STA® anti-Xa liquid (95% CI, 0.99, 1.00). Correlation was lower in rivaroxaban concentrations below 50 μg L-1 and above 200 μg L-1 . The overall bias of the Bland-Altman difference plot was 14.7 μg L-1 for Biophen Heparin, 17.9 μg L-1 for Biophen DiXal and 19.0 μg L-1 for STA anti-Xa liquid. Agreement between laboratories was high at peak level but limited at trough level. Conclusions Anti-Xa activity correlated well with rivaroxaban plasma concentrations, especially in a range between 50 and 200 μg L-1 . However, anti-Xa assays systematically overestimated rivaroxaban concentration as compared with HPLC-MS, particularly at higher concentrations. This overestimation, coupled with an apparent interindividual variation, might affect the interpretation of results in some situations.

The anticoagulant effect of heparin during radiofrequency ablation (RFA) in patients taking apixaban or rivaroxaban

PURPOSE

Measuring the anticoagulant effect of heparin during radiofrequency ablation (RFA) in patients taking apixaban and rivaroxaban is challenging, since the activated coagulation time (ACT) does not seem to reflect the true anticoagulant activity of these drugs. We therefore evaluated coagulation properties of apixaban and rivaroxaban during RFA by different coagulation assays to better monitor periprocedural hemostasis.

METHODS

The study included 90 patients (61 ± 12 years) with atrial fibrillation who underwent RFA procedures. Patients received 20 mg rivaroxaban (n = 73) once or 5 mg apixaban (n = 17) twice daily 4 weeks prior to the procedure. During RFA, unfractionated heparin i.v. was given to maintain an ACT of 250-300 s. Blood samples were taken before and 10, 60, and 360 min after heparin administration.

RESULTS

Heparin displayed a lower anti-Xa activity in rivaroxaban-treated patients compared to apixaban-treated patients. In contrast, D-dimer and prothrombin fragment F1+2 plasma levels indicated a higher activation of the coagulation cascade in apixaban/heparin than in rivaroxaban/heparin patients. This discordant coagulative state measured in vitro had no clinical impact in terms of bleeding or thromboembolic complications.

CONCLUSION

We found different biochemical responses to rivaroxaban/heparin and apixaban/heparin during RFA. Precaution is necessary when monitoring periprocedural hemostasis in DOAC patients to avoid mismanagement.

Clinical pearls: Laboratory assessments of direct oral anticoagulants (DOACS)

Direct oral anticoagulants (DOACS) are being used for stroke prevention in patients with atrial fibrillation as well as for prophylaxis and treatment of venous thromboembolism. Clinicians who treat, or may encounter, patients with DOAC exposure, should be aware of the limitations of coagulation testing in this setting, and seek counsel from their laboratory to understand the effects of DOACS on coagulation results. Generally, assays that employ clot based principles, or methods that require thrombin or Factor Xa activation or substrates may be affected by the presence of DOACS. The clinical laboratory should have an algorithmic testing plan for adequately assessing the presence of all DOACS and readily provide this information to clinicians. We describe Clinical Pearls for DOAC assessment using common and esoteric coagulation testing.

Perioperative management of patients on direct oral anticoagulants

Direct oral anticoagulants (DOACs) have been licensed worldwide for several years for various indications. Each year, 10-15% of patients on oral anticoagulants will undergo an invasive procedure and expert groups have issued several guidelines on perioperative management in such situations. The perioperative guidelines have undergone numerous updates as clinical experience of emergency management has increased and perioperative studies including measurement of residual anticoagulant levels have been published. The high inter-patient variability of DOAC plasma levels has challenged the traditional recommendation that perioperative DOAC interruption should be based only on the elimination half-life of DOACs, especially before invasive procedures carrying a high risk of bleeding. Furthermore, recent publications have highlighted the potential danger of heparin bridging use when DOACs are stopped before an invasive procedure. As antidotes are progressively becoming available to manage severe bleeding or urgent procedures in patients on DOACs, accurate laboratory tests have become the standard to guide their administration and their actions need to be well understood by clinicians. This review aims to provide a systematic approach to managing patients on DOACs, based on recent updates of various perioperative guidance, and highlighting the advantages and limits of recommendations based on pharmacokinetic properties and laboratory tests.

ANMCO Position Paper: the use of non-vitamin K dependent new oral anticoagulant(s) in pulmonary embolism therapy and prevention

The new oral anticoagulants (NOACs) have radically changed the approach to the treatment and prevention of thromboembolic pulmonary embolism. The authors of this position paper face, in succession, issues concerning NOACs, including (i) their mechanism of action, pharmacodynamics, and pharmacokinetics; (ii) the use in the acute phase with the 'double drug single dose' approach or with 'single drug double dose'; (iii) the use in the extended phase with demonstrated efficacy and with low incidence of bleeding events; (iv) the encouraging use of NOACs in particular subgroups of patients such as those with cancer, the ones under- or overweight, with renal insufficiency (creatinine clearance > 30 mL/min), the elderly (>75 years); (v) they propose a possible laboratory clinical pathway for follow-up; and (vi) carry out an examination on the main drug interactions, their potential bleeding risk, and the way to deal with some bleeding complications. The authors conclude that the use of NOACs both in the acute phase and in the extended phase is equally effective to conventional therapy and associated with fewer major bleeding events, which make their use in patients at higher risk of recurrences safer.

Laboratory Assessment of the Anticoagulant Activity of Direct Oral Anticoagulants: A Systematic Review

BACKGROUND

Direct oral anticoagulants (DOACs) are the treatment of choice for most patients with atrial fibrillation and/or noncancer-associated venous thromboembolic disease. Although routine monitoring of these agents is not required, assessment of anticoagulant effect may be desirable in special situations. The objective of this review was to summarize systematically evidence regarding laboratory assessment of the anticoagulant effects of dabigatran, rivaroxaban, apixaban, and edoxaban.

METHODS

PubMed, Embase, and Web of Science were searched for studies reporting relationships between drug levels and coagulation assay results.

RESULTS

We identified 109 eligible studies: 35 for dabigatran, 50 for rivaroxaban, 11 for apixaban, and 13 for edoxaban. The performance of standard anticoagulation tests varied across DOACs and reagents; most assays, showed insufficient correlation to provide a reliable assessment of DOAC effects. Dilute thrombin time (TT) assays demonstrated linear correlation (r2 = 0.67-0.99) across a range of expected concentrations of dabigatran, as did ecarin-based assays. Calibrated anti-Xa assays demonstrated linear correlation (r2 = 0.78-1.00) across a wide range of concentrations for rivaroxaban, apixaban, and edoxaban.

CONCLUSIONS

An ideal test, offering both accuracy and precision for measurement of any DOAC is not widely available. We recommend a dilute TT or ecarin-based assay for assessment of the anticoagulant effect of dabigatran and anti-Xa assays with drug-specific calibrators for direct Xa inhibitors. In the absence of these tests, TT or APTT is recommended over PT/INR for assessment of dabigatran, and PT/INR is recommended over APTT for detection of factor Xa inhibitors. Time since last dose, the presence or absence of drug interactions, and renal and hepatic function should impact clinical estimates of anticoagulant effect in a patient for whom laboratory test results are not available.

Reversal of direct oral anticoagulants: a practical approach

Direct oral anticoagulants (DOACs) have at least noninferior efficacy compared with other oral anticoagulants and have ancillary benefits, including overall better safety profiles, lack of the need for routine monitoring, rapid onset of action, and ease of administration. Reversal of these agents may be indicated in certain situations such as severe bleeding and for perioperative management. DOAC-associated bleeding should be risk stratified: patients with moderate or severe bleeding should have the DOAC discontinued and reversal strategies should be considered. Laboratory testing has limited utility in the acute management of bleeding; thrombin time and activated partial thromboplastin time may be useful for excluding clinically relevant levels of dabigatran. Prothrombin time is potentially useful for rivaroxaban and edoxaban, but calibrated anti-Xa assays are optimal for determining clinically relevant levels of factor Xa inhibitors. Because specific reversal agents are not widely available, supportive care and interventions for local hemostasis remain the cornerstones of therapy in the patient with DOAC-associated bleeding. Nonspecific reversal agents should be considered only in the event of severe bleeding because their efficacy is unknown, and they are associated with risk of thrombosis. Recent results from phase 3/4 studies demonstrate efficacy for an antidote to dabigatran (idarucizumab, a monoclonal antibody fragment with specificity for dabigatran) and an antidote to factor Xa inhibitors (andexanet alfa, a recombinant and inactive form of factor Xa that binds inhibitors). A universal reversal agent (ciraparantag) for many anticoagulants, including the DOACs, shows promise in results from phase 1 and 2 studies.