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Despite a higher safety profile compared to vitamin K antagonists, rivaroxaban therapy is still connected with multiple adverse effects, such as a high risk of bleeding. Thus, therapeutic drug monitoring (TDM) of rivaroxaban concentrations is suggested. An alternative to plasma samples can be dried blood spots (DBS), which minimize the cost of sample storage and transport. In this study, we developed a UPLC-MS/MS method for the analysis of rivaroxaban in DBS and plasma samples. Chromatographic separation was achieved on a Zorbax Eclipse Plus C18 column (2.1 × 100 mm; 3.5 µm, Agilent Technologies Inc., Santa Clara, CA, USA) with a mobile phase consisting of water and acetonitrile, both containing 0.1% formic acid. The analytes were detected using a positive ionization mode by multiple reaction monitoring. We validated the method according to ICH guidelines. The precision and accuracy were satisfactory. Extraction recovery was approximately 57% and 66% for DBS and plasma samples, respectively. A high correlation between rivaroxaban concentrations in plasma and DBS samples collected from patients was confirmed with Deming regression. The suitability of both sampling techniques for the rivaroxaban TDM was also verified by Bland-Altman plots based on DBS-predicted and observed plasma concentrations. In addition, we found a significant relationship between rivaroxaban concentrations and coagulation parameters, including prothrombin time (PT) and international normalized ratio (INR).

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., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2020 International Anesthesia Research Society.)

The attractiveness of direct oral anticoagulants (DOACs) over vitamin K antagonists, in addition to a better benefit-risk ratio, stems from the fact that no therapeutic drug monitoring is deemed necessary. This has been recently mitigated by the fact that increased dabigatran (D) plasma levels have been associated with hemorrhages, and is currently under scrutiny of the European Medicines Agency. We aimed to evaluate, in real conditions of use, whether patients with out-of-range DOAC blood concentrations (too high or too low) were associated with bleeding or thrombosis. Patients treated with D or rivaroxaban (R) were prospectively included in a hospital cohort. D and R plasma levels were measured by high-pressure liquid chromatography-tandem mass spectrometry-at the physician's demand. We defined concentration range as "expected" within the 95% confidence interval of the mean concentration obtained from pivotal trials, and "out of range" when concentrations were outside of that interval. A blind assessment of concentrations versus occurrence of bleeding or thrombosis was performed by means of univariate and multivariate analysis. Three hundred and twenty-two patients (mean age 78.5 years ± 13.1), treated with D or R were included consecutively. They had a mean CHA2DS2-VASc at 4.4 ± 1.7 and a mean HAS-BLED score at 1.7 ± 0.9. Irrespective of the DOAC prescribed, patients presenting with out-of-range concentrations had significantly more bleeding or thrombosis than patients with expected concentrations (P < 0.001). Patients with bleeding were more prone to have concentrations beyond the 95 percentile (N = 62, P < 0.001), whereas patients with thrombosis were more likely to have concentrations below the fifth percentile (N = 26, P < 0.05). The main risks associated with hemorrhages were abnormal concentrations, a high HAS-BLED score, the patient's age, and the creatinine blood level. For thrombosis, a concentration below the fifth percentile was the only risk factor that was significant in our cohort. While D and R under current recommendation have a better benefit-risk ratio than warfarin, their safe usage could be further optimized by some degree of therapeutic monitoring.

Objective: Although rivaroxaban has recently become widely used for thrombosis treatment, it is difficult for clinicians to make clinical decisions in critical situations, such as emergent surgery or interventions, because a specific anti-Xa assay is not available in many laboratories. This study assessed the relationships between rivaroxaban-specific anti-factor Xa activity (AXA) and unfractionated heparin (UFH)-specific AXA and determined the cutoff level for UFH-specific AXA in critical situations for patients undergoing rivaroxaban therapy., Methods: Thirty-eight blood samples were collected from patients with cancer-associated thrombosis receiving rivaroxaban therapy. All samples were assessed using both rivaroxaban-specific and UFH-specific anti-Xa assays. Routine coagulation studies, including prothrombin time (PT) and activated partial thromboplastin time, were also conducted on the samples., Results: A positive dose-dependent correlation between rivaroxaban-specific and UFH-specific AXA was evident (R = 0.97; P < .0001). Rivaroxaban-specific AXA was also positively correlated with PT (R = 0.95; P < .0001) but only weakly with activated partial thromboplastin time (R = 0.67; P < .0001). Patients with plasma rivaroxaban concentrations <100 ng/mL were found to have UFH-specific AXA <1.41 IU/mL and PT <17.3 seconds, with sensitivities of 100% and 93.3% and specificities of 87.0% and 95.7%, respectively., Conclusions: Our study demonstrates that UFH-calibrated AXA correlates strongly with plasma rivaroxaban concentration. This assay appears to be sensitive to the presence of rivaroxaban, which may be advantageous in the setting of assessing drug levels for critical events. These findings suggest that if a rivaroxaban-specific anti-Xa assay is unavailable, the chromogenic anti-Xa assay for UFH may be useful to assess the anticoagulant effects of rivaroxaban., (Copyright © 2020 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.)

Anticoagulant plasma concentrations and patient characteristics might affect the benefit-risk balance of therapy. The study objective was to assess the impact of model-predicted rivaroxaban exposure and patient characteristics on outcomes in patients receiving rivaroxaban for venous thromboembolism (VTE) prophylaxis (VTE-P) after hip/knee replacement surgery. Post hoc exposure-response analyses were conducted using data from the phase 3 RECORD1-4 studies, in which 12,729 patients were randomized to rivaroxaban 10 mg once daily or enoxaparin for ≤ 39 days. Multivariate regression approaches were used to correlate model-predicted individual rivaroxaban exposures and patient characteristics with outcomes. In the absence of measured rivaroxaban exposure, exposure estimates were predicted based on individual increases in prothrombin time (PT) and by making use of the known correlation between rivaroxaban plasma concentration and dynamics of PT. No significant associations between rivaroxaban exposure and total VTE or major bleeding were identified. A significant association between exposure and a composite of major or non-major clinically relevant (NMCR) bleeding from day 4 after surgery was observed. The relationship was shallow, with an approximate predicted absolute increase in a composite of major or NMCR bleeding from 1.08 [95% confidence interval (CI) 0.76-1.54] to 2.18% (95% CI 1.51-3.17) at the 5th and 95th percentiles of trough plasma concentration, respectively. In conclusion, based on the underlying data and analysis, no reliable target window for exposure with improved benefit-risk could be identified within the investigated exposure range. Hence, monitoring rivaroxaban levels is unlikely to be beneficial in VTE-P.

Rivaroxaban exposure and patient characteristics may affect the rivaroxaban benefit-risk balance. This study aimed to quantify associations between model-predicted rivaroxaban exposure and patient characteristics and efficacy and safety outcomes in patients with non-valvular atrial fibrillation (NVAF), using data from the phase 3 ROCKET AF trial (NCT00403767). In ROCKET AF, 14,264 patients with NVAF were randomized to rivaroxaban (20 mg once daily [OD], or 15 mg OD if creatinine clearance was 30-49 mL/min) or dose-adjusted warfarin (median follow-up: 707 days); rivaroxaban plasma concentration was measured in a subset of 161 patients. In this post hoc exposure-response analysis, a multivariate Cox model was used to correlate individual predicted rivaroxaban exposures and patient characteristics with time-to-event efficacy and safety outcomes in 7061 and 7111 patients, respectively. There was no significant association between model-predicted rivaroxaban trough plasma concentration (C trough ) and efficacy outcomes. Creatinine clearance and history of stroke were significantly associated with efficacy outcomes. C trough was significantly associated with the composite of major or non-major clinically relevant (NMCR) bleeding (hazard ratio [95th percentile vs. median]: 1.26 [95% confidence interval 1.13-1.40]) but not with major bleeding alone. The exposure-response relationship for major or NMCR bleeding was shallow with no clear threshold for an acceleration in risk. History of gastrointestinal bleeding had a greater influence on safety outcomes than C trough . These results support fixed rivaroxaban 15 mg and 20 mg OD dosages in NVAF. Therapeutic drug monitoring is unlikely to offer clinical benefits in this indication beyond evaluation of patient characteristics.

Anticoagulant plasma concentrations and patient characteristics might affect the benefit-risk balance of therapy. This study assessed the impact of model-predicted rivaroxaban exposure and patient characteristics on outcomes in patients receiving rivaroxaban for venous thromboembolism treatment (VTE-T) using data from the phase 3 EINSTEIN-DVT and EINSTEIN-PE studies. In the absence of measured rivaroxaban exposure, exposure estimates were predicted based on individual increases in prothrombin time (PT) and the known correlation between rivaroxaban plasma concentrations and PT dynamics. The composite efficacy outcomes evaluated were recurrent deep-vein thrombosis (DVT) and pulmonary embolism (PE) and recurrent DVT, PE and all-cause death; safety outcomes were major bleeding and the composite of major or non-major clinically relevant (NMCR) bleeding. Exposure-response relationships were evaluated using multivariate logistic and Cox regression for the twice-daily (BID) and once-daily (OD) dosing periods, respectively. Predicted rivaroxaban exposure and CrCl were significantly associated with both efficacy outcomes in the BID period. In the OD period, exposure was significantly associated with recurrent DVT and PE but not recurrent DVT, PE and all-cause death. The statistically significant exposure-efficacy relationships were shallow. Exposure-safety relationships were absent within the investigated exposure range. During both dosing periods, low baseline hemoglobin and prior bleeding were associated with the composite of major or NMCR bleeding. In conclusion, based on the underlying data and analysis, no reliable target window for exposure with improved benefit-risk could be identified within the investigated exposure range. Therefore, monitoring rivaroxaban levels is unlikely to be beneficial in VTE-T.

Purpose: There is little evidence to guide the use of direct oral anticoagulants (DOACs) in patients with class III obesity. Clinicians face the dilemma that using DOACs in patients with class III obesity may not provide adequate anticoagulation, while avoiding DOACs may deprive them of a useful therapeutic option. We present 2 cases describing our experience navigating rivaroxaban use in patients with class III obesity and review available case reports of measurement of rivaroxaban levels using a calibrated anti-factor Xa assay., Summary: In patient case 1, the rivaroxaban trough level was within the reference range, and therapy was continued. In patient case 2, the rivaroxaban trough level was below the reference range, and the patient's anticoagulation therapy was switched to warfarin. No thromboembolic events were noted in the 2 patients more than 1 year (15 and 22 months, respectively) after initiation of anticoagulation therapy. Because of the many advantages associated with use of DOACs instead of vitamin K antagonists, further research is critical to enabling clinicians to use DOACs more confidently in a broader population., Conclusion: When monitoring rivaroxaban therapy in patients with class III obesity, there is uncertainty regarding clinical interpretation of drug levels that fall outside of established reference ranges, and monitoring is not standardized or widely available. In addition to case reports found in the literature, the presented cases highlight these challenges and differing clinical decisions made when evaluating rivaroxaban levels in patients with class III obesity., (© American Society of Health-System Pharmacists 2020. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Pharmacokinetic studies and therapeutic drug monitoring of anticoagulants require a simple, rapid, and reliable analytical method for monitoring plasma concentrations. The aims of the current work were to develop and validate a liquid chromatography/tandem mass spectrometry method for the simultaneous determination of 3 direct oral anticoagulants (dabigatran, rivaroxaban, and apixaban) in human plasma that is suitable for pharmacokinetic studies and routine therapeutic drug monitoring in busy hospital laboratories., Methods: This method included a hydrolysis step to account for the active acylglucuronide metabolites of dabigatran that demonstrate an equivalent anticoagulant effect as dabigatran. After hydrolysis, a simple one-step protein precipitation was used for sample preparation. Total dabigatran (the sum of free dabigatran and the contribution from dabigatran acylglucuronides), rivaroxaban, and apixaban, and their corresponding isotopically labeled internal standards were resolved on a C18(2) column. All compounds were detected using electrospray ionization liquid chromatography/tandem mass spectrometry in the positive mode., Results: For all 3 anticoagulants, standard curves were linear over the concentration range of 1.0-1000 mcg/L (r > 0.99), bias was < ±10%, and intraday and interday coefficients of variation (imprecision) were <10%. The limit of quantification was 1.0 mcg/L. For all 3 anticoagulants and corresponding isotopically labeled internal standards, the absolute recoveries were similar and consistent, with mean values of 93%-102%. No significant matrix effects were observed., Conclusions: This method is simple, rapid, robust, and reliable and can be used to analyze the plasma concentrations of the drugs in patients on dabigatran or rivaroxaban therapy.

Essentials Direct oral anticoagulants (DOAC) are used for stroke and venous thromboembolism prevention. We report a new assay that measures anti-factor Xa DOAC levels in plasma and whole blood. Rivaroxaban and apixaban can be accurately quantified below trough levels. The ease and accuracy of the assay demonstrate its potential for point-of-care applications., Background: Rivaroxaban and apixaban are the most commonly used anti-factor (F) Xa direct oral anticoagulants (DOAC), with indications for prevention of stroke in nonvalvular atrial fibrillation as well as treatment and prevention of venous thromboembolism. However, lacking is accessibility to a detection method that is able to quantify low levels of anti-FXa DOACs., Objective: We report a new assay that measures anti-FXa DOAC levels in plasma and whole blood., Methods: This is achieved by the use of a prothrombin derivative that is labeled with a fluorescent probe (Flu-II), which then acts as the macromolecular substrate to measure residual FXa activity. The Flu-II cleavage is then initiated by the addition of a solution containing FXa, FVa, and phospholipid vesicles composed of 75% PC and 25% PS (PCPS) vesicles with calcium, in the presence of hirudin to prevent feedback activity by the native thrombin generated. The Flu-II cleavage is monitored by fluorescence in real time where the initial rate of fluorescence change is inversely proportional to DOAC levels., Results: In plasma systems, the assay demonstrates dose-response between 0 and 5 nmol/L rivaroxaban and between 0 and 10 nmol/L apixaban. Corn trypsin inhibitor did not affect this assay. With individual plasma samples, the assay showed excellent consistency and reproducibility. From 2 μL of whole blood, the assay showed dose-response between 0 and 2 nmol/L of DOACs in the final mixture of 100 μL, thus representing up to 100 nmol/L in circulating blood., Conclusion: The assay is ideal for rapidly and accurately measuring DOAC levels in plasma and blood, demonstrating its potential for point-of-care applications., (© 2019 International Society on Thrombosis and Haemostasis.)

The aim of the study was to evaluate the diagnostic accuracy of thromboelastometry for assessing rivaroxaban concentrations. The accuracy of thromboelastometry was compared with the high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method, which is the gold standard for drug plasma monitoring (the reference standard). Forty-six clinically stable patients were treated with 10, 15, or 20 mg of rivaroxaban once daily (OD group) or 15 mg twice a day (BID group) (no particular indication for treatment). Patient samples were collected 2 h after the use of the medication (peak) and 2 h before the next dose (trough). The rivaroxaban plasma concentrations were determined via HPLC-MS/MS, and thromboelastometry was performed using a ROTEM® delta analyzer. There were significant prolongations in clotting time (CT) for the 10, 15, and 20 mg of rivaroxaban treatments in the OD groups. In the 15 mg BID group, the responses at the peak and trough times were similar. At the peak times, there was a positive correlation between the plasma concentration of rivaroxaban and CT (Spearman correlation rho=0.788, P<0.001) and clot formation time (rho=0.784, P<0.001), and a negative correlation for alpha angle (rho=-0.771, P<0.001), amplitude after 5 min (rho=-0.763, P<0.001), and amplitude after 10 min (rho=-0.680, P<0.001). The CT presented higher specificity and sensitivity using the cut-off determined by the receiver characteristics curve. ROTEM has potential as screening tool to measure possible bleeding risk associated with rivaroxaban plasma levels.

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.

Essentials Direct oral anticoagulants (DOACs) do not require laboratory monitoring currently. DOAC specific measurements were performed at trough in patients with atrial fibrillation. Patients who developed thromboembolic events showed lower DOAC plasma levels. This study supports the concept of measuring DOAC levels at steady state., Summary: Background Direct oral anticoagulants (DOACs) are administered at fixed doses without the need for dose adjustment according to laboratory testing. High interindividual variability in drug blood levels has been shown with all DOACs. To evaluate a possible relationship between DOAC C-trough anticoagulant levels and thromboembolic events, 565 consecutive naive patients with atrial fibrillation (AF) were enrolled in this study performed within the START Laboratory Registry. Methods DOAC-specific measurements (diluted thrombin time or anti-activated factor II calibrated for dabigatran; anti-activated FX calibrated for rivaroxaban or apixaban) at C-trough were performed locally at steady state within 15-25 days after the start of treatment. For each DOAC, the interval of C-trough levels, from the limit of quantification to the highest value, was subdivided into four equal classes, and results were attributed to these classes; the median values of results were also calculated. Thromboembolic complications occurring during 1 year of follow-up were recorded. Results Thromboembolic events (1.8%) occurred in 10 patients who had baseline C-trough levels in the lowest class of drug levels. The incidence of thromboembolic events among patients with DOAC C-trough levels in the lowest level class was 2.4%, and that in the remaining groups was 0%. The patients with thrombotic complications also had a higher mean CHA 2 DS 2 -VASc score than that of the total patient population: 5.3 (95% confidence interval [CI] 4.3-6.3 versus 3.0 (95% CI 2.9-3.1). Conclusion In this study cohort, thrombotic complications occurred only in DOAC-treated AF patients who had very low C-trough levels, with a relatively high CHA 2 DS 2 -VASc score. Larger studies are warranted to confirm these preliminary observations., (© 2018 The Authors. Journal of Thrombosis and Haemostasis published by Wiley Periodicals, Inc. on behalf of International Society on Thrombosis and Haemostasis.)

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., (© 2017 International Society on Thrombosis and Haemostasis.)

Reliable detection of anticoagulation status in patients treated with non-vitamin K antagonist oral anticoagulants (NOACs) is challenging but of importance especially in the emergency setting. This study evaluated the potential of a whole-blood clotting time assay based on Surface Acoustic Waves (SAW-CT) in stroke-patients. The SAW-technology was used for quick and homogenous recalcification of whole blood inducing a surface-activated clotting reaction quantified and visualised by real-time fluorescence microscopy with automatic imaging processing. In 20 stroke or transient ischaemic attack (TIA)-patients taking NOACs kinetics of SAW-CT were assessed and correlated to other coagulation parameters (PT, aPTT) and NOAC-plasma concentration measured by tandem mass spectrometry (LC-MS/MS). In 225 emergency patients with suspicion of acute stroke or TIA, SAW-CT values were assessed. Mean (± SD) SAW-CT in non-anticoagulated stroke patients (n=180) was 124 s (± 21). In patients on dabigatran or rivaroxaban, SAW-CT values were significantly higher 2 and 8 hours (h) after intake rising up to 267 seconds (s) (dabigatran, 2 h after intake) and 250 s (rivaroxaban, 8 h after intake). In patients on apixaban, SAW-CT values were only moderately increased 2 h after intake (SAW-CT 153 s). In emergency patients, SAW-CT values were significantly higher in NOAC and vitamin K antagonist (VKA)-treated as compared to non-anticoagulated patients. In conclusion, the SAW-CT assay is capable to monitor anticoagulant level and effect in patients receiving dabigatran, rivaroxaban and the VKA phenprocoumon. It has a limited sensitivity for apixaban-detection. If specific SAW-CT results were used as cut-offs, SAW-CT yields high diagnostic accuracy to exclude relevant rivaroxaban and dabigatran concentrations in stroke-patients.

Direct oral anticoagulants (DOACs) can be quantified using methods that can be performed in any clinical or research laboratory using manual or automated instrument platforms. Dabigatran etexilate, the oral direct thrombin inhibitor, can be quantified by drug-calibrated clot or chromogenic-based assays using either thrombin or ecarin as substrates. Oral direct anti-Xa inhibitors, such as rivaroxaban, apixaban, and edoxaban, can be quantified with drug-calibrated anti-Xa kits or reagents as typically used for measuring heparins (unfractionated, low molecular weight, or pentasaccharides).

Plasma levels of Rivaroxaban (RivLev) might be useful to guide therapeutic decisions in patients with acute stroke under Rivaroxaban. A prerequisite for the potential clinical usefulness is their rapid availability in emergency situations. Single-center explorative analysis from the Novel-Oral-Anticoagulants-in-Stroke-Patients-registry (NOACISP, cinicaltrials.gov:NCT02353585). We included consecutive patients with acute ischemic or hemorrhagic stroke under Rivaroxaban (last intake <48 h) in which RivLev determined by an automated anti-factor Xa-based chromogenic assay (Hyphen-Biomed, France) are available. Primary endpoint was the turnaround time (TAT), defined as time from registration of the blood sample in the lab to first result published. Furthermore, we studied, whether TAT is influenced by (1) on- and off-hour-measurements and (2) early versus later patient arrival (cut-off: 270 min after symptom onset). Thirty-eight patients met the eligibility criteria (mean age 77 years, 44 % female). TAT was 34 min (IQR 29-65 min). TATs were similar for on- (n = 14; median 34 min; IQR 30-56 min) and off-hours-TATs (n = 24; median 35 min; IQR 29-75 min) as well as for early (n = 16; median 33 min; IQR 30-40 min) and late patient arrival (n = 22, median 34 min, IQR 28-58 min; all nonsignificant.). Taking into account RivLev in the decision process about the use of intravenous thrombolysis, three patients received intravenous thrombolysis on an individualized basis, none of them with bleeding complications. Emergency measurement of RivLev among patients with acute stroke is available within a median of 34 min and therefore feasible for ED use. Due to the rapid availability, further research to evaluate the role of RivLev in order to guide acute treatment decisions is warranted.

Most studies on the sensitivities of coagulation assays to direct oral anticoagulants (DOACs) are based on normal plasma spiked with anticoagulant in the laboratory. Recent studies have shown that reagent sensitivity varies significantly depending on whether spiked or patient samples are used. The aim of this study was to compare the sensitivities of routine coagulation assays in patient samples and commercial drug specific calibrators using commonly used activated partial thromboplastin time (APTT) and prothrombin time (PT) reagents (i.e., Actin FS and Neoplastine CI Plus for APTT and PT, respectively) in Australian laboratories. Samples collected at Pathology North Hunter (PN-H) for dabigatran (n=39), rivaroxaban, (n=56) or apixaban levels (n=22) between February 2013 and November 2015 were analysed and compared to two different commercial drug specific calibrators from different manufacturers for each DOAC. Our results show that dabigatran (Hyphen and Technoclone) and rivaroxaban (Stago) calibrators tend to overestimate the APTT but are similar to patient samples for PT. A cut-off DOAC level of 50 ng/mL based on results from patient samples within the laboratory can be used as the lower limit which will result in prolongation of APTT for dabigatran (sensitivity 96%, n=25) and PT for rivaroxaban (sensitivity 97%, n=29), respectively. Individual laboratories should be familiar with the sensitivity of their coagulation reagents to different DOACs including differences between patient samples versus different commercial drug specific calibrators., (Copyright © 2016 Royal College of Pathologists of Australasia. All rights reserved.)

We performed a review of all direct oral anticoagulant (DOAC) levels - ecarin times for dabigatran and anti-Xa levels for rivaroxaban and apixaban - ordered at our institution with the purpose of evaluating DOAC levels from "real-world" (non-clinical trial) patients taking DOACs long-term, in order to assess levels obtained, reasons for checking levels, and actions taken based on the testing result. A total of 28 patients had 48 levels sent over a 36-month period. The majority of outpatient levels were within or close to the range of published values. The setting in which levels were sent influenced how results affected management decisions: in the outpatient setting, the majority of levels served to reassure clinicians that DOAC levels were within expected ranges resulting in continuation of chosen management, whereas in the inpatient setting, DOAC levels were used most frequently to detect DOAC presence in urgent clinical situations and influenced clinical decision-making in the peri-procedural and pre-operative periods. Our results demonstrate that while testing may be useful if immediately available in urgent clinical situations where assessment of drug presence is needed, DOAC level monitoring is infrequently used overall, and the lack of use combined with the paucity of available evidence to guide clinical decision-making based on the results suggests there is little urgency to make the tests widely available for routine use outside of acute settings in the emergency department and urgent surgical setting., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Background: Rivaroxaban (Xarelto) does not require routine coagulation monitoring; however, in certain clinical situations (overdose, drug accumulation, urgent surgery) measurement of its plasma concentration is highly recommended. Currently, there is no single hemostasis test that shows a direct correlation between rivaroxaban plasma levels and anticoagulant efficacy., Objectives: This study was intended to assess the value of ROTEM in determining rivaroxaban administration., Material and Methods: Thirteen patients with venous thromboembolism and 13 healthy volunteers were compared with regard to certain ROTEM parameters and anti-FXa activity. The tests were done before the administration of 20 mg rivaroxaban (i.e. 24 h after previous administration) and 2.5 h afterwards., Results: The study group demonstrated residual activity of rivaroxaban in plasma (20 ± 11.3 ng/mL) 24 h following the previous administration, which did not cause marked changes in clotting assays compared to controls. In the group, 2.5 h after rivaroxaban administration, prolongation of PT (PTratio 1.51 ± 0.22), APTT (APPTratio: 1.30 ± 0.14) and ROTEM CT (CTratio - EXTEM: 2.45 ± 1.06, CTratio -, Intem: 1.32 ± 0.21) were observed. The cut-off values for particular tests were created to determine if the patient had achieved desirable anticoagulant effect after rivaroxaban administration. The mean anti-FXa values were significantly lower in patients before rivaroxaban dosing than after., Conclusions: PT demonstrated better diagnostic value than APTT in rivaroxaban administration. The ROTEM clotting time (CT) according to EXTEM may be used to determine the anticoagulation effect of rivaroxaban, but is not sensitive enough to measure the residual activity of this drug.

Aim: This study evaluated the influence of rivaroxaban 20 mg once daily on international normalized ratio (INR) during the co-administration period when switching from rivaroxaban to warfarin., Methods: We developed a calibrated coagulation model that was qualified with phase I clinical data. Prothrombin time and INR values were simulated by use of phospholipid concentrations that matched Neoplastin Plus® and Innovin® reagents. To simulate the combined effects of rivaroxaban and warfarin on INR during switching, warfarin initiation was simulated by adjusting the magnitude of the warfarin effect to reach the desired target INRs over the course of 21 days. The warfarin effect values (obtained every 6 h) and the desired rivaroxaban plasma concentrations were used. Nomograms were generated from rivaroxaban induced increases in INR., Results: The simulation had good prediction quality. Rivaroxaban induced increases in the total INR from the warfarin attributed INR were seen, which increased with rivaroxaban plasma concentration. When the warfarin only INR was 2.0-3.0, the INR contribution of rivaroxaban with Neoplastin Plus® was 0.5-1.2, decreasing to 0.3-0.6 with Innovin® at median trough rivaroxaban plasma concentrations (38 μg l(-1) )., Conclusions: The data indicate that measuring warfarin induced changes in INR are best performed at trough rivaroxaban concentrations (24 h after rivaroxaban dosing) during the co-administration period when switching from rivaroxaban to warfarin. Furthermore, Innovin® is preferable to Neoplastin Plus® because of its substantially lower sensitivity to rivaroxaban, thereby reducing the influence of rivaroxaban on the measured INR., (© 2014 The British Pharmacological Society.)

Background: Dilute Russell Viper Venom Time (DRVV-T) might be useful in urgent settings for screening patients on Non-VKA Oral Anticoagulants (NOACs)., Aim: To compare the accuracy of DRVV-T with gold standard assays for the assessment of pharmacodynamics of dabigatran, rivaroxaban and vitamin K antagonist (VKA) in plasma samples from patients., Methods: Sixty rivaroxaban, 48 dabigatran and 50 VKA samples from patients were included. DRVV-T was performed in all groups using STA®-Staclot®DRVV-Screen and -Confirm. For NOACs, PT and aPTT were performed using different reagents while plasma drug concentrations were measured by liquid mass-spectrometry (LC-MS/MS). For VKA, INR was performed using RecombiPlasTin 2G®., Results: For NOACs, correlations between calibrated STA®-Staclot®DRVV-Confirm and LC-MS/MS (rs=0.88 and 0.97 for rivaroxaban and dabigatran, respectively) were higher than the ones obtained with STA®-Staclot®DRVV-Screen (rs=0.87 and 0.91), PT (rs=0.83 to 0.86) or aPTT (rs=0.84 to 0.89). Bland Altman analyses showed that calibrated DRVV-T methods tend to overestimate plasma concentrations of NOACs. ROC curves revealed that cut-off to exclude supra-therapeutic levels at Ctrough (i.e. 200ng/mL) are different for dabigatran and rivaroxaban. Neither STA®-Staclot®DRVV-Screen nor -Confirm correlated sufficiently with the intensity of VKA therapy (rs=0.35 and 0.52)., Conclusions: STA®-Staclot®DRVV-Confirm provides a rapid estimation of the intensity of anticoagulation with rivaroxaban or dabigatran without specific calibrators. At Ctrough, thresholds for rivaroxaban and dabigatran can be used to identify supra-therapeutic plasma level. However, this test cannot differentiate the nature of the NOACs. The development of a point-of-care device optimising this method would be of particular interest in emergency situations., (Copyright © 2015 Elsevier Ltd. All rights reserved.)