Assessment of the impact of rivaroxaban on coagulation assays: laboratory recommendations for the monitoring of rivaroxaban and review of the literature

A specific fluorescence resonance energy quenching-based biosensor for measuring thrombin activity in whole blood

BACKGROUND

At sites of vessel injury, thrombin acts as the central mediator of coagulation by catalyzing fibrin clot formation and platelet activation. Thrombin generation is most frequently measured in plasma samples using small-molecule substrates; however, these have low specificity for thrombin and limited utility in whole blood. Plasma assays are limited because they ignore the hemostatic contributions of blood cells and require anticoagulation and the addition of supraphysiological concentrations of calcium.

OBJECTIVES

To overcome these limitations, we designed and characterized a fluorescence resonance energy quenching-based thrombin sensor (FTS) protein.

METHODS

The fluorescence resonance energy quenching pair of mAmetrine and tTomato, separated by a thrombin recognition sequence, was developed. The protein was expressed using Escherichia coli, and purity was assessed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The cleavage of FTS was monitored by fluorescence using excitation at 406 nm and emission at 526 nm and 581 nm.

RESULTS

Compared with small-molecule substrates, the FTS demonstrated high specificity for thrombin; it is not cleaved by thrombin or inhibited by α2-macroglobulin and interacts with thrombin's anion-binding exosite I. The FTS can effectively measure thrombin generation in plasma and in finger-prick whole blood, which allows it to be developed into a point-of-care test of thrombin generation. The FTS does not inhibit standard thrombin-generation assays. Lastly, FTS-based thrombin generation in nonanticoagulated finger-prick blood was delayed but enhanced compared with that in citrated plasma.

CONCLUSION

The FTS will broaden our understanding of thrombin generation in ways that are not attainable with current methods.

Thromboembolic prevention in athletes: management of anticoagulation in sports players affected by atrial fibrillation

Atrial fibrillation (AF) is a common cardiac arrhythmia that poses a significant risk of stroke and thromboembolic events. Anticoagulation therapy is essential for preventing stroke in patients with AF. An increasing number of people of all ages, including cardiac patients, approach physical activity as both a leisure-time exercise and a competitive sport. Therefore, patients at risk of AF are increasingly allowed to practice sports activities. Management of oral anticoagulant therapy (OAT) in these patients is extremely challenging because of the need to balance the risks and benefits of medications, considering both hemorrhagic (in case of trauma) and ischemic complications when the drugs are avoided. Official recommendations are limited for these patients and forbid sports that increase the risk of trauma and consequent bleeding in most cases. These recommendations are strongly influenced by the "traditional" management of OAT, which mainly involves coumarin derivatives. Non-vitamin K antagonist direct oral anticoagulants (DOACs), with their more favorable pharmacokinetic-pharmacodynamic profile than that of coumarin derivatives, may represent an opportunity to modify the approach to sports activity in patients with AF and indications for OAT. This study aimed to review the use of anticoagulants in athletes with AF, highlight their efficacy and safety, and provide practical considerations regarding their management.

A comparative in vitro study of the anticoagulant effect of branded versus generic rivaroxaban

BACKGROUND

Several generic formulations of rivaroxaban were recently marketed to be used interchangeably with their branded equivalent. However, there have been no previously published studies that directly compared the in vitro anticoagulant effect of branded vs. generic rivaroxaban. The aim of this in vitro study was to compare the effects of three raw rivaroxaban materials, obtained from the branded (Xarelto®) and two generic (Rivarolto® and Rivaroxaban Sandoz®) rivaroxaban formulations on an array of coagulation assays.

METHODS

A pool of normal plasma was spiked with several concentrations of the three rivaroxaban (range 50-750 ng/ml). The concentrations were assessed with a rivaroxaban calibrated anti-Xa assay and confirmed by ultra-high-performance liquid chromatography-mass spectrometry coupled with tandem mass spectrometry (UHPLC-MS/MS). The following assays were performed: Prothrombin time (PT), activated Partial Thromboplastin time (aPTT), Diluted Russell's Viper Venom Test (dRVVT), Thrombin time (TT), Clauss Fibrinogen, Factor VII, VIII and IX assays, and thromboelastography.

RESULTS

The results obtained by the three rivaroxaban at similar concentrations were comparable. Increasing concentrations of the three rivaroxaban showed a strong positive correlation with the PT, aPTT and dRVVT assays (r > 0.95, p < 0.01 for all), and a strong negative correlation with the Factors assays (r < -0.95, p < 0.01 for all). TT and Clauss Fibrinogen were not affected by rivaroxaban. No significant difference was identified in the mean assays' results obtained by the three rivaroxaban.

CONCLUSION

This study showed that the branded and generic rivaroxaban exert an identical in vitro anticoagulant effect across a wide range of concentrations.

Coumarins as factor XIIa inhibitors: Potency and selectivity improvements using a fragment-based strategy

Previously, we described weak coumarin inhibitors of factor XIIa, a promising target for artificial surface-induced thrombosis and various inflammatory diseases. In this work, we used fragment-based drug discovery approach to improve our coumarin series. First, we screened about 200 fragments for the S1 pocket. The S1 pocket of trypsin-like serine proteases, such as factor XIIa, is highly conserved and is known to drive a major part of the association energy. From the screening, we selected fragments displaying a micromolar activity and studied their selectivity on other serine proteases. Then, these fragments were merged to our coumarin templates, leading to the generation of nanomolar inhibitors. The mechanism of inhibition was further studied by mass spectrometry demonstrating the covalent binding through the formation of an acyl enzyme complex. The most potent compound was tested in plasma to evaluate its stability and efficacy on coagulation assays. It exhibited a plasmatic half-life of 1.9 h and a good selectivity for the intrinsic coagulation pathway over the extrinsic one.

Mutant CYP3A4/5 Correlated with Clinical Outcomes by Affecting Rivaroxaban Pharmacokinetics and Pharmacodynamics in Patients with Atrial Fibrillation

PURPOSE

This study was designed to investigate the impact of single-nucleotide polymorphism-encoded cytochrome P450 enzymes (CYP3A4/5) on clinical outcomes of rivaroxaban in patients with non-valvular atrial fibrillation (NVAF) based on pharmacokinetics and pharmacodynamics (PK/PD) aspects.

METHOD

A prospective study enrolling 165 rivaroxaban-treated patients with NVAF was conducted. Genotyping of CYP3A4 (rs2242480, rs2246709, rs3735451, and rs4646440) and CYP3A5 (rs776746) was performed to explore their impact on the trough plasma concentrations (Ctrough) of rivaroxaban, coagulation indicators at the Ctrough including activated partial thromboplastin time (APTT) and prothrombin time (PT), and clinical outcomes.

RESULTS

Patients with mutant genotype CYP3A4 (rs2242480, rs2246709, and rs3735451) and CYP3A5 (rs776746) had higher levels of rivaroxaban Ctrough, PT values than that of wild-type. Furthermore, a positive relationship was revealed between Ctrough and PT (r = 0.212, p = 0.007), while no significant correlation was found between Ctrough and APTT. Regarding the clinical outcomes, the minor allele carriers on rs3735451 and the minor allele (A) carriers on rs2246709 were associated with higher incidence of minor bleeding (p = 0.028 and p = 0.038, respectively) and were identified as the independent risk factors of minor bleeding treated with rivaroxaban (p = 0.024 and p = 0.036, respectively), with the receiver operating characteristic (ROC) curve validated (AUC = 0.8956, 95% CI: 0.829-0.962).

CONCLUSION

The CYP3A4 polymorphisms (rs2242480, rs2246709, and rs3735451) and CYP3A5 rs776746 were associated with variations in rivaroxaban PK/PD. The minor allele (C) carriers on rs3735451 and the minor allele (A) carriers on rs2246709 were correlated with clinical outcomes.

Pediatric Thromboprophylaxis of Large Coronary Artery Aneurysm Using Rivaroxaban

Giant or large coronary artery aneurysms (CAA) are rare in children, most often secondary to Kawasaki disease, and anticoagulation is recommended to prevent thromboembolism. There are no published pediatric reports on the use of a direct oral anticoagulant for this indication. We describe the anticoagulation management of an 8-year-old boy with a dilated right CAA secondary to Kawasaki disease that has remained stable on rivaroxaban and aspirin, following bleeding complications on enoxaparin and challenges on warfarin. The use of rivaroxaban appears to be safe and effective in the prevention of thrombosis in a pediatric patient with CAA.

Acquired Hemophilia A Masquerading as Bleeding on Anticoagulation: A Case Report Including Key Laboratory Considerations

We report a case of a patient with recurrent hematomas while on anticoagulation for a pulmonary embolism and a prolonged hospital stay due to a delayed diagnosis for acquired hemophilia A. Acquired hemophilia A is a rare autoimmune bleeding disorder with autoantibodies directed against coagulation factor VIII (FVIII), leading to an acquired FVIII deficiency. A prolonged isolated activated partial thromboplastin time (aPTT) in a bleeding patient warrants workup for acquired hemophilia A. This is specifically challenging in patients with thrombosis on anticoagulation and can lead to significant delays in diagnosis and associated morbidities. The case highlights the need for further awareness of this disease, potential laboratory pitfalls when conducting and interpreting coagulation assays, and the management considerations in a patient with a simultaneous thrombotic and hemorrhagic condition.

How to assess parallelism in factor assays: coefficient of variation of results with different dilutions or slope ratio?

INTRODUCTION

Non-parallelism in factor assays can lead to incorrect factor activities. Parallelism can be assessed by calculating the coefficient of variation (CV) of results obtained on 3 dilutions of the same sample. Some authors have proposed that if there is <15% then the average activity is reportable. Some analysers use a slope ratio (SR) to calculate parallelism, with an acceptance range of approximately 0.9-1.1.

METHODS

We evaluated CV and SR in one stage FII-FXII assays on Sysmex CS5100i using Innovin or Actin FS. Frozen normal and pathological plasmas, plasmas containing Direct Oral Anticoagulants, Direct Thrombin Inhibitors or Lupus Anticoagulant were analysed to assess possible non-parallelism.

RESULTS

In plasmas with factor levels >25 IU/dl (plus no interfering substances) all CVs were < 15%. One sample (low factor activities 10-15 IU/dl), had CVs > 15% in FII, FVII and FXII assays only. SR outside of 0.9-1.1 were seen in FII and FXII assays at different levels of clotting factor including some within the normal range. Non-parallelism was detected more frequently with SR than CV for those with interfering substances.

CONCLUSIONS

SR outside of 0.9-1.1 were seen in different levels of clotting factors, including samples which did not contain interfering substances. The target of 15% CV was a better discriminator than a SR for acceptance. When factor levels were reduced to around 10-15 IU/dl, a target 20 %CV was more appropriate than 15%. It might be appropriate for laboratories to assess locally whether their acceptance criteria need to be wider at low levels of clotting factors.

DOAC-associated bleeding, hemostatic strategies, and thrombin generation assays - a review of the literature

Direct oral anticoagulants (DOACs) account for most oral anticoagulant use. DOAC-associated bleeding events are commonly encountered in clinical practice and are associated with substantial morbidity and mortality. Both specific reversal agents and nonspecific hemostatic therapies, such as prothrombin complex concentrates, are used in the management of DOAC-associated bleeding. Measuring hemostatic efficacy and demonstrating a clinical impact from these therapies among studies of bleeding patients is challenging. Thrombin generation assays provide information on the total hemostatic potential of plasma, and have emerged as a promising modality to both measure the impact of DOACs on coagulation and to evaluate the effects of hemostatic therapies among patients with DOAC-associated bleeding. The mechanisms by which nonspecific hemostatic agents impact coagulation and thrombin generation in the context of DOAC therapy are unclear. As a result, we undertook a review of the literature using a systematic search strategy with the goal of summarizing the effects of DOACs on thrombin generation and the effects of both specific reversal agents and nonspecific hemostatic therapies on DOAC-altered thrombin generation parameters. We sought to identify clinical studies focusing on whether altered thrombin generation is associated with clinical bleeding and whether correction of altered thrombin generation parameters predicts improvements in clinical hemostasis. Lastly, we sought to outline future directions for the application of thrombin generation assays toward anticoagulation therapies and the question of anticoagulation reversal.

The effect of rivaroxaban on biomarkers in blood and plasma: a review of preclinical and clinical evidence

Rivaroxaban is a direct, oral factor Xa inhibitor that is used for the prevention and treatment of various thromboembolic disorders. Several preclinical and clinical studies have utilized specific molecules as biomarkers to investigate the potential role of rivaroxaban beyond its anticoagulant activity and across a range of biological processes. The aim of this review is to summarize the existing evidence regarding the use of blood-based biomarkers to characterize the effects of rivaroxaban on coagulation and other pathways, including platelet activation, inflammation and endothelial effects. After a literature search using PubMed, almost 100 preclinical and clinical studies were identified that investigated the effects of rivaroxaban using molecular biomarkers. In agreement with the preclinical data, clinical studies reported a trend for reduction in the blood concentrations of D-dimers, thrombin-antithrombin complex and prothrombin fragment 1 + 2 following treatment with rivaroxaban in both healthy individuals and those with various chronic conditions. Preclinical and also some clinical studies have also reported a potential impact of rivaroxaban on the concentrations of platelet activation biomarkers (von Willebrand factor, P-selectin and thrombomodulin), endothelial activation biomarkers (matrix metalloproteinase-9, intercellular adhesion molecule-1 and vascular cell adhesion molecule-1) and inflammation biomarkers (interleukin-6, tumor necrosis factor-α and monocyte chemoattractant protein-1). Based on the results of biomarker studies, molecular biomarkers can be used in addition to traditional coagulation assays to increase the understanding of the anticoagulation effects of rivaroxaban. Moreover, there is preliminary evidence to suggest that rivaroxaban may have an impact on the biological pathways of platelet activation, endothelial activation and inflammation; however, owing to paucity of clinical data to investigate the trends reported in preclinical studies, further investigation is required to clarify these observations.

The Role of Anti-Factor Xa Activity in the Management of Ecchymosis in Patients Receiving Rivaroxaban after Total Knee Arthroplasty

This study aims to evaluate the efficacy of anti-factor Xa activity (aFXa) in predicting ecchymosis after total knee arthroplasty (TKA). One hundred and two unilateral primary TKA patients were recruited consecutively in this prospective observational study. Participants received rivaroxaban (10 mg p.o. qd) from postoperative day 1 (POD1) to POD35 and were divided into a non-ecchymosis group (group A) and an ecchymosis group (group B). AFXa was assessed as the primary outcome on POD1 and POD3. Prothrombin time (PT), activated partial thromboplastin time (APTT) and thromboelastography (TEG) were recorded both preoperatively and postoperatively (on POD1 and POD3). Other outcomes, including venous thromboembolism (VTE), blood loss and wound complications were also collected and compared. As a result, 27.5% of the participants (n = 28) were allocated into group B. Demographic data were comparable between the two groups. The aFXa levels in group B were significantly higher than those in group A on POD1 and POD3, and the aFXa level was assessed as an independent risk factor for ecchymosis. The cut-off value of aFXa was determined to be 121.38 ng/mL at maximal Youden index, associated with area under the receiver operating characteristics curve of 0.67. Group B experienced significantly more blood loss and wound complications than group A. No statistical difference was detected regarding PT, APTT and TEG parameters. AFXa is a promising parameter to predict ecchymosis after TKA. Patients with aFXa > 121.38 ng/mL should be considered as high-risk population for postoperative ecchymosis and may require intense monitoring or dosage modification of anticoagulants.

Evaluation of newly-developed modified diluted prothrombin time reagent in non-valvular atrial fibrillation patients with direct oral anticoagulants: A comparative study with conventional reagents

INTRODUCTION

A single assay to assess the effect of the direct FXa inhibitor is needed clinically because prothrombin (PT) assay is not yet sensitive enough for accurate evaluation. We developed modified diluted prothrombin time (mdPT) assay showing a high reactivity to direct FXa inhibitors based on prothrombin time (PT) reagent. The purpose of this study was to evaluate the reactivity of mdPT to direct FXa inhibitors comparing to that of commercial PT reagents and diluted prothrombin time (dPT).

METHODS

The correlation and slopes of mdPT against the drug concentrations by anti-Xa assay were compared to those of the four commercial reagents of PT or dPT in 275, 257, and 243 clinical samples collected from non-valvular atrial fibrillation (NVAF) patients who are prescribed apixaban, edoxaban or rivaroxaban for stroke prevention, respectively.

RESULTS

The correlation coefficient (95% confidence interval) of mdPT against apixaban, edoxaban, and rivaroxaban was 0.818 (0.775-0.854), 0.914 (0.892-0.932), and 0.814 (0.766-0.852), respectively. The slope (95% confidence interval) of mdPT for apixaban, edoxaban, and rivaroxaban was 0.0068 (0.0063-0.0075), 0.0076 (0.0072-0.0080), and 0.0072 (0.0065-0.0078), respectively, which were higher than that of four commercial PT and dPT reagents, ranging within 0.0006-0.0023, 0.0017-0.0038, and 0.0016-0.0057 (all, p < 0.001), respectively.

CONCLUSION

Compared with other PT and dPT reagents, mdPT reagent showed sharper slope to all direct FXa inhibitors, and higher correlation to apixaban and comparable correlation to edoxaban and rivaroxaban. This new reagent is expected to be a coagulation screening assay having a consistently high response to any types of direct FXa inhibitors.

Coagulation assays and direct oral anticoagulant levels among patients having an elective surgery or procedure

BACKGROUND

The Perioperative Anticoagulation Use for Surgery Evaluation study prospectively evaluated a prespecified periprocedural interruption strategy of direct oral anticoagulants (DOACs) among patients with atrial fibrillation. Coagulation testing is widely available and frequently requested prior to invasive procedures. Coagulation assays display poor sensitivity to clinically relevant DOAC concentrations.

OBJECTIVES

Determine the utility of routinely available coagulation testing at predicting a DOAC concentration of <30 ng/ml among patients in the preprocedural setting.

METHODS

We calculated the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and positive and negative likelihood ratio (LR+ and LR-) of a normal coagulation assay result for identifying patients with a preprocedural DOAC level < 30 ng/ml.

RESULTS

We identified weak or very weak correlations between coagulation assay results and DOAC levels in the preprocedural setting, except for a moderate correlation between the thrombin time (TT) and dabigatran concentrations (ρ = 0.68; p < .001). The prothrombin time (PT) and activated partial thromboplastin time (APTT) demonstrated modest sensitivity (78.9% to 88.2%) and PPVs (76.4% to 93.1%) but poor specificity (13.2% to 53.3%) and NPVs (16.3% to 30.2%) across all three DOACs. A normal TT was associated with 100% specificity and PPV values for a dabigatran level < 30 ng/ml. A normal APTT among patients on dabigatran was associated with an LR+ of 1.671 (95% confidence interval [CI] 1.297, 2.154) and an LR- of 0.395 (95% CI 0.207, 0.751) for levels <30 ng/ml.

CONCLUSIONS

The PT and APTT perform poorly at safely identifying patients with negligible DOAC levels in the preprocedural setting.

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.

Application of plasma metabolome for monitoring the effect of rivaroxaban in patients with nonvalvular atrial fibrillation

Rivaroxaban, an oral factor Xa inhibitor, has been used to treating a series of thromboembolic disorders in clinical practice. Measurement of the anticoagulant effect of rivaroxaban is important to avoid serious bleeding events, thus ensuring the safety and efficacy of drug administration. Metabolomics could help to predict differences in the responses among patients by profiling metabolites in biosamples. In this study, plasma metabolomes before and 3 hours after rivaroxaban intake in 150 nonvalvular atrial fibrillation (NVAF) patients and 100 age/gender-matched controls were analyzed by liquid chromatography coupled with mass spectrometry (LC-MS/MS). When compared with controls, a total of thirteen plasma metabolites were differentially expressed in the NVAF patients. Pathway analysis revealed that purine and lipid metabolism were dysregulated. A panel of three metabolites (17a-ethynylestradiol, tryptophyl-glutamate and adenosine) showed good predictive ability to distinguish nonvalvular atrial fibrillation with an area under the receiver operating characteristic curve (AUC) of 1 for the discovery phase and 1 for validation. Under rivaroxaban treatment, a total of seven metabolites changed, the lipid and glycosylphosphatidylinositol biosynthesis pathways were altered and the panel consisting of avocadene, prenyl glucoside and phosphatidylethanolamine showed predictive ability with an AUC of 0.86 for the discovery dataset and 0.82 for the validation. The study showed that plasma metabolomic analyses hold the potential to differentiate nonvalvular atrial fibrillation and can help to monitor the effect of rivaroxaban anticoagulation.

The edoxaban‐M4 metabolite and measurement of edoxaban by chromogenic assays in human plasma

Introduction

Edoxaban is the only anti-Xa inhibitor metabolized in pharmacologically active moiety that could interfere with chromogenic anti-Xa assays, especially in case of drug-drug interactions or physiological disorders.

Materials and methods

We evaluated the contribution of the main metabolite of edoxaban, edoxaban-M4 (M4), in 79 plasma samples from patients taking edoxaban. The total anti-Xa activity was evaluated on three different chromogenic factor Xa-based assays. Results were compared with a validated ultra-high-performance liquid chromatography coupled with a tandem mass spectrometry measurement. Edoxaban and its active M4 metabolite have also been spiked separately in normal pooled plasma to assess the sensitivity of chromogenic anti-Xa assays to both molecules individually.

Results

Spiked edoxaban or M4 provided different slopes of linear regression models between chromogenic and chromatographic measurement (from 0.97 for STA Liquid Anti-Xa to 1.10 for Biophen Heparin LRT Low with edoxaban and from 0.70 for Biophen DiXaI High to 0.83 for Biophen Heparin LRT High, respectively). A positive correlation is observed between the increase of the ratio M4/edoxaban with the difference between chromogenic and chromatographic measurements.

Conclusion

Edoxaban and M4 do not similarly impact chromogenic assays, leading to biased chromogenic estimations of ponderal concentrations. In patient samples, this impact is even more important at low concentrations or in the case of an increase in the M4/edoxaban ratio because of hepatic or renal impairments or in case of drug interactions. This study highlights the limitations and risks of error of expressing results in ponderal concentrations instead of global activity anti-Xa.

Inherited Thrombophilia in the Era of Direct Oral Anticoagulants

Severe inherited thrombophilia includes rare deficiencies of natural anticoagulants (antithrombin and proteins C and S) and homozygous or combined factor V Leiden and FII G20210A variants. They are associated with a high thrombosis risk and can impact the duration of anticoagulation therapy for patients with a venous thromboembolism (VTE) event. Therefore, it is important to diagnose thrombophilia and to use adapted anticoagulant therapy. The widespread use of direct anticoagulants (DOACs) for VTE has raised new issues concerning inherited thrombophilia. Concerning inherited thrombophilia diagnosis, DOACs are directed toward either FIIa or FXa and can therefore interfere with coagulation assays. This paper reports DOAC interference in several thrombophilia tests, including the assessment of antithrombin, protein S, and protein C activities. Antithrombin activity and clot-based assays used for proteins C and S can be overestimated, with a risk of missing a deficiency. The use of a device to remove DOACs should be considered to minimize the risk of false-negative results. The place of DOACs in the treatment of VTE in thrombophilia patients is also discussed. Available data are encouraging, but given the variability in thrombosis risk within natural anticoagulant deficiencies, evidence in patients with well-characterized thrombophilia would be useful.

From Activated Partial Thromboplastin Time to Antifactor Xa and Back Again

OBJECTIVES

Monitoring is essential to safe anticoagulation prescribing and requires close collaboration among pathologists, clinicians, and pharmacists.

METHODS

We describe our experience in the evolving strategy for laboratory testing of unfractionated heparin (UFH).

RESULTS

An intrainstitutional investigation revealed significant discordance between activated partial thromboplastin time (aPTT) and antifactor Xa (anti-Xa) assays, prompting a transition from the former to the latter in 2013. With the increasing use of oral factor Xa inhibitors (eg, apixaban, rivaroxaban, edoxaban, betrixaban), which interfere with the anti-Xa assay, we adapted our protocol again to incorporate aPTT in patients admitted on oral Xa inhibitors who require transition to UFH.

CONCLUSIONS

Our experience demonstrates key challenges in anticoagulation and highlights the importance of clinical pathologists in helping health systems adapt to the changing anticoagulation landscape.

Updates on Anticoagulation and Laboratory Tools for Therapy Monitoring of Heparin, Vitamin K Antagonists and Direct Oral Anticoagulants

Anticoagulant drugs have been used to prevent and treat thrombosis. However, they are associated with risk of hemorrhage. Therefore, prior to their clinical use, it is important to assess the risk of bleeding and thrombosis. In case of older anticoagulant drugs like heparin and warfarin, dose adjustment is required owing to narrow therapeutic ranges. The established monitoring methods for heparin and warfarin are activated partial thromboplastin time (APTT)/anti-Xa assay and prothrombin time – international normalized ratio (PT-INR), respectively. Since 2008, new generation anticoagulant drugs, called direct oral anticoagulants (DOACs), have been widely prescribed to prevent and treat several thromboembolic diseases. Although the use of DOACs without routine monitoring and frequent dose adjustment has been shown to be safe and effective, there may be clinical circumstances in specific patients when measurement of the anticoagulant effects of DOACs is required. Recently, anticoagulation therapy has received attention when treating patients with coronavirus disease 2019 (COVID-19). In this review, we discuss the mechanisms of anticoagulant drugs—heparin, warfarin, and DOACs and describe the methods used for the measurement of their effects. In addition, we discuss the latest findings on thrombosis mechanism in patients with COVID-19 with respect to biological chemistry.

Current use of rivaroxaban in elderly patients with venous thromboembolism (VTE)

Venous thromboembolism (VTE), which is characterized by pulmonary embolism and deep vein thrombosis, has become a serious public concern. Notably, over half of the patients with VTE are over 70 years of age, but elderly patients are at high risk of anti-coagulation and bleeding, which increase with age. Moreover, risk factors and frailty also show a difference between elderly patients and ordinary patients diagnosed with VTE. Rivaroxaban is a direct inhibitor of activated factor Xa and has the advantage of predictable pharmacodynamics and pharmacokinetics, no coagulation monitoring, and few drug interactions. As a first-line therapy for VTE, this drug is more advantageous than traditional therapy and exhibits good efficacy and safety for ordinary patients. However, the effectiveness and safety of rivaroxaban in elderly patients have not been fully elucidated. This article reviewed the use of rivaroxaban in elderly patients, including drug interactions, monitoring, reversal agents of rivaroxaban, and the use of small dosages of rivaroxaban in elderly patients.

Direct oral anticoagulants in point-of-care monitoring: an ex-vivo study

BACKGROUND

Anticoagulatory activity of direct oral anticoagulants (DOACs) is not routinely measurable by point-of-care monitoring. Thus, the aim of this study was to evaluate the influence of dabigatran/rivaroxaban on point-of-care testing.

METHODS

Samples from 34 participants under DOAC therapy were drawn at two time points. Before ingestion and two-to-three hours afterwards. Thrombelastometric (ROTEM) and aggregometric (Multiplate) measurements were performed. Dabigatran and rivaroxaban plasma levels were determined.

RESULTS

Dabigatran and rivaroxaban plasma levels showed significant correlations with clotting time (CT) in EXTEM (r=0.765, P<0.0001; r=0.689, P<0.0001) and INTEM (r=0.792, P<0.0001; r=0.595, P<0.001). A positive correlation was identified between dabigatran ingestion and maximum-clot-firmness (MCF) (r=0.354, P<0.05) in the EXTEM test, pronounced in the absence of concomitant antiplatelet therapy (r=0.709, P<0.05). EXTEM-MCF positively correlated with the TRAP test in aggregometry (0.662, P<0.05), an effect not observed in patients treated with antiplatelet therapy.

CONCLUSIONS

Prolongation of CT-EXTEM and CT-INTEM indicates delayed initiation of clot formation. The CT-EXTEM seems to facilitate qualitative monitoring of dabigatran. In contrast, qualitative monitoring of rivaroxaban by CT-EXTEM may be limited as rivaroxaban may affect the measurement at therapeutic plasma levels. It seems that clot formation is faster/firmer in the presence of increased dabigatran plasma levels. This can be attributed to a non-dose-dependent effect via increased fibrin polymerization and second to a dose-dependent effect via increased platelet sensitivity to thrombin.

Effects of dabigatran and rivaroxaban on stroke severity according to the results of routine coagulation tests

Introduction

Prior use of direct oral anticoagulants has been associated with reduced stroke severity in patients with non-valvular atrial fibrillation (NVAF). The aim of this study was to investigate the impact of prothrombin time (PT) and activated partial thromboplastin time (aPTT) on stroke severity in patients who were receiving dabigatran or rivaroxaban at the time of stroke onset.

Materials and methods

We enrolled 107 patients with NVAF who developed acute ischemic stroke while on dabigatran or rivaroxaban and presented within 24 hours to nine hospitals between January 2014 and December 2018. The results of PT and aPTT assays were obtained within 24 hours of stroke onset in all patients. We analyzed PT and aPTT in relation to stroke severity and ischemic lesion volume using correlation and multivariable regression analyses.

Results

Of the 107 patients included, 46 (43.0%) were on dabigatran and 61 (57.0%) were on rivaroxaban. In patients with prior dabigatran use, while aPTT was inversely correlated with admission National Institutes of Health Stroke Scale (NIHSS) score (r = -0.369, p = 0.012) and ischemic lesion volume (r = -0.480, p = 0.005), there was no correlation between PT and either of these variables. Multivariable analysis confirmed the existence of a significant independent inverse relationship between aPTT and NIHSS score at admission (B, -0.201; 95% confidence interval [CI], -0.370 to -0.032; p = 0.005) and between aPTT and ischemic lesion volume (B, -0.076; 95% CI, -0.130 to -0.023; p = 0.007). In patients with prior rivaroxaban use, neither PT nor aPTT was associated with admission NIHSS score or ischemic lesion volume in the correlation and multivariable analyses.

Conclusions

In patients with NVAF who were receiving dabigatran, prolonged aPTT was associated with reduced stroke severity.

Comprehensive review of the impact of direct oral anticoagulants on thrombophilia diagnostic tests: Practical recommendations for the laboratory

There is a laboratory and clinical need to know the impact of direct oral anticoagulants (DOACs) on diagnostic tests to avoid misinterpretation of results. Although the regulatory labelling documents provide some information about the influences of each DOAC on diagnostic tests, these are usually limited to some of the most common tests and no head to head comparison is available. In this paper, we report the impact of DOACs on several thrombophilia tests, including assessment of antithrombin, protein S and protein C activity assays, detection of activated protein C resistance and assays used for lupus anticoagulant. Results are compared and discussed with data obtained from literature. The final goal of this comprehensive review is to provide practical recommendations for laboratories to avoid misdiagnosis due to oral direct factor Xa (FXa) or IIa (FIIa) inhibitors. Overall, oral direct FXa (apixaban, betrixaban, edoxaban and rivaroxaban) and FIIa (dabigatran) antagonists may affect clot-based thrombophilia diagnostic tests resulting in false-positive or false-negative results. An effect on FIIa-based thrombophilia diagnostic tests is observed with dabigatran but not with anti-FXa DOACs and conversely for FXa-based thrombophilia diagnostic tests. No impact was observed with antigenic/chromogenic methods for the assessment of protein S and C activity. In conclusion, interpretation of thrombophilia diagnostic tests results should be done with caution in patients on DOACs. The use of a device/chemical compound able to remove or antagonize the effect of DOACs or the development of new diagnostic tests insensitive to DOACs should be considered to minimize the risk of false results.

Treatment with rivaroxaban and monitoring of coagulation profiles in two dogs with venous thromboembolism

Two dogs with immune-mediated hemolytic anemia complicated with thromboembolism were presented. Both of the dogs were initially treated with immunosuppressive therapy in conjunction with dalteparin and clopidogrel. Although the immunosuppressive therapy was effective, peritoneal effusion due to thromboembolism was observed during the course of the disease in these dogs. After initiation of rivaroxaban treatment, peritoneal effusion decreased immediately in parallel with the normalization of D-dimer, antithrombin (AT), and thrombin-antithrombin complex (TAT). Hematochezia, cutaneous hemorrhage, and hematuria were observed as adverse events after administration of rivaroxaban in one case. Rivaroxaban was effective for the control of thromboembolism secondary to immune-mediated hemolytic anemia, and D-dimer, AT, and TAT were useful to monitor the status of thromboembolic disease in dogs.

Perioperative management of anticoagulation

Periprocedural management of the anticoagulated patient can be as easy as continuing warfarin for a low bleeding risk procedure, holding a direct oral anticoagulant for 1 day prior and resuming 1 day later or as complex as emergent reversal with prothrombin complex concentrate, idarucizumab, or andexanet alfa. Patient-specific factors for thromboembolic risk and procedural bleeding risk determine timing of anticoagulation hold prior to and resumption after invasive procedures. Clinical trials and management studies in recent years have helped inform our approach to these patients, but much of the guidance is still based on expert consensus.

Novel Pheretima guillelmi-derived antithrombotic protein DPf3: Identification, characterization, in vitro evaluation and antithrombotic mechanisms investigation

In this study, the antithrombotic protein, named DPf3, was purified from Pheretima guillelmi by ion-exchange chromatography. The protein pattern of DPf3 was mainly at 26-34 kDa; its two main proteins, DPf3 ID NO.1 and NO.2, were detected to be 36,121.745 Da and 24,485.004 Da consisting of 329 and 241 amino acids, respectively; the full covered protein sequences were consistent with Ac44553_g1_i1_1 and Dc43026_g1_i1_2 in our previous constructed P. guillelmi local database. The secondary structure of DPf3 is the mixture of α-helix (0.19), β-sheet (0.30) and random coil (0.51). DPf3 was predicted to possess a direct effect on fibrin, fibrinogen and plasminogen by protein-protein docking analysis, which was further confirmed by in vitro and ex vivo study. DPf3 was determined to possess antithrombotic ability by showing outstanding direct-hydrolysis ability on fibrin, fibrinogen and blood clot, and slight plasminogen activation activity. DPf3 could significantly prolong APTT and decrease fibrinogen content, indicating that DPf3 exerted antithrombotic activity via the intrinsic and/or common pathway, and the third coagulation phase. By this approach, the functional protein DPf3 was fully revealed and found to confer excellent anticoagulant and thrombolytic activity, and could be developed into a promising antithrombotic agent.

Laboratory monitoring of rivaroxaban in Chinese patients with deep venous thrombosis: a preliminary study

Background

Rivaroxaban, a novel oral anticoagulant drug, is widely used in clinical practice. There is no standardized laboratory monitoring for rivaroxaban, and its plasma concentration in Chinese patients with deep vein thrombosis is unclear. The rivaroxaban concentrations in human plasma and determine the steady-state concentration of rivaroxaban in patients with deep vein thrombosis are needed.

Methods

An ultra-high-performance liquid chromatography with mass spectrometric detection method was developed. Chromatographic separation was performed on a Waters BEH C18 column with isocratic elution using a mobile phase composed of acetonitrile and water. Quantitation of the analytes was performed using positive ionization mode and mass transitions of m/z 437.3 → m/z 145.0 and m/z 440.1 → m/z 145.0 for rivaroxaban and the internal standard, respectively. Blood samples were collected at 0 h and 2 h after patients took rivaroxaban for 7 days or more.

Results

The method was validated over the concentration range of 0.5 ~ 400 ng•mL^− 1 with a very low limit of quantification of 0.5 ng·mL^− 1, and the intra- and inter-day precision (RSD%) were < 15%. The range of the steady state concentration in patients that took 15 mg rivaroxaban twice daily, 10 mg twice daily, 20 mg once daily, 15 mg once daily, and 10 mg once daily were 168.5 ~ 280.1 ng•mL^− 1, 74.2 ~ 271.4 ng•mL^− 1, 25.7 ~ 306.8 ng•mL^− 1, 24.5 ~ 306.4 ng•mL^− 1, and 15.4 ~ 229.2 ng•mL^− 1, respectively.

Conclusions

The plasma rivaroxaban concentration in patients who took 10 mg rivaroxaban twice daily fluctuated less than that in patients who took 20 mg rivaroxaban once daily. The plasma concentration can be used for therapeutic drug monitoring for rivaroxaban.

Practical issues in measuring the anticoagulant effect of direct oral anticoagulants

The classical oral anticoagulants are increasingly being replaced in clinical practice by new antithrombotic drugs, which act by enabling direct inhibition of coagulation factor IIa (FIIa) or factor Xa (FXa). These drugs have multiple acronyms, including NOACs (new, non-vitamin K antagonist) or DOACs (direct oral anticoagulants), and currently include dabigatran (FIIa inhibitor), and rivaroxaban, apixaban, and edoxaban (FXa inhibitors). These drugs are approved for stroke prevention in patients with non-valvular atrial fibrillation and the prevention and treatment of venous thromboembolism. The "mantra" that DOACs do not require laboratory monitoring is not entirely correct because laboratory testing for drug effects is needed in many situations, because they influence hemostasis tests and in situations in which urgent measurement of DOACs is required. This should be very important to consider in the clinical situation for numbers of indications and increasing numbers of patients on DOACs therapy. The main aim of this article is to provide practical issues to general laboratory testing for DOACs, as well as to help avoid diagnostic errors associated with hemostasis testing. The assays for DOAC quantification must be available in medical centers on a whole day basis, to facilitate optimal drug management in conditions when things go wrong or in urgent cases of immediate reversal of anticoagulation or appropriate administration of a specific antidote.

The 2018 European Heart Rhythm Association Practical Guide on the use of non-vitamin K antagonist oral anticoagulants in patients with atrial fibrillation

The current manuscript is the second update of the original Practical Guide, published in 2013 [Heidbuchel et al. European Heart Rhythm Association Practical Guide on the use of new oral anticoagulants in patients with non-valvular atrial fibrillation. Europace 2013;15:625-651; Heidbuchel et al. Updated European Heart Rhythm Association Practical Guide on the use of non-vitamin K antagonist anticoagulants in patients with non-valvular atrial fibrillation. Europace 2015;17:1467-1507]. Non-vitamin K antagonist oral anticoagulants (NOACs) are an alternative for vitamin K antagonists (VKAs) to prevent stroke in patients with atrial fibrillation (AF) and have emerged as the preferred choice, particularly in patients newly started on anticoagulation. Both physicians and patients are becoming more accustomed to the use of these drugs in clinical practice. However, many unresolved questions on how to optimally use these agents in specific clinical situations remain. The European Heart Rhythm Association (EHRA) set out to coordinate a unified way of informing physicians on the use of the different NOACs. A writing group identified 20 topics of concrete clinical scenarios for which practical answers were formulated, based on available evidence. The 20 topics are as follows i.e., (1) Eligibility for NOACs; (2) Practical start-up and follow-up scheme for patients on NOACs; (3) Ensuring adherence to prescribed oral anticoagulant intake; (4) Switching between anticoagulant regimens; (5) Pharmacokinetics and drug-drug interactions of NOACs; (6) NOACs in patients with chronic kidney or advanced liver disease; (7) How to measure the anticoagulant effect of NOACs; (8) NOAC plasma level measurement: rare indications, precautions, and potential pitfalls; (9) How to deal with dosing errors; (10) What to do if there is a (suspected) overdose without bleeding, or a clotting test is indicating a potential risk of bleeding; (11) Management of bleeding under NOAC therapy; (12) Patients undergoing a planned invasive procedure, surgery or ablation; (13) Patients requiring an urgent surgical intervention; (14) Patients with AF and coronary artery disease; (15) Avoiding confusion with NOAC dosing across indications; (16) Cardioversion in a NOAC-treated patient; (17) AF patients presenting with acute stroke while on NOACs; (18) NOACs in special situations; (19) Anticoagulation in AF patients with a malignancy; and (20) Optimizing dose adjustments of VKA. Additional information and downloads of the text and anticoagulation cards in different languages can be found on an EHRA website (www.NOACforAF.eu).

Diagnosis and management of congenital thrombophilia in the era of direct oral anticoagulants

Direct oral anticoagulants (DOAC)s are often preferred to other anticoagulants as they are more practical and do not require routine laboratory monitoring. Less is known about their use in congenital thrombophilia. Efficacy of DOACs in congenital thrombophilia, effect of DOACs and other anticoagulants on diagnostic tests as well as efficacy and safety of anticoagulant use in this population is still a matter of debate. In this review we intended to analyze the potential pitfalls of testing for thrombophilia in patients using DOACs and vitamin K antagonists (VKA)s as well as to suggest strategies to improve diagnostic accuracy in this setting. We also reviewed the literature for evidence regarding the safety and efficacy of DOACs in patients with congenital thrombophilia. Some evidence was found supporting the use of DOACs in low risk thrombophilia, although evidence for their use in high risk thrombophilia is limited to small series and case reports. Our findings support the generation of better evidence to support DOAC use for congenital thrombophilia, especially in the high risk subgroups.

Concomitant assessment of rivaroxaban concentration and its impact on thrombin generation

BACKGROUND

Reliable assays to measure direct oral anticoagulant (DOAC) levels and their activity in critical situations are needed. Drug levels alone are not representative of the effect of DOACs on an individual's coagulation. We developed a technique that provides direct assessment of the global effect of rivaroxaban on the individual's coagulation in addition to plasma concentrations.

METHODS

DOAC concentrations were determined in fifty patients using rivaroxaban, with the new assay, Xross-CAT. The effect of rivaroxaban on coagulation (activity) was measured with thrombin generation (TG) in platelet poor plasma using 5 pM tissue factor on the same device. The levels were validated with the Biophen DiXal assay. The prothrombin time (PT) and dilute Russell viper venom time (dRVVT) were performed to estimate the effect on coagulation.

RESULTS

The variability of Xross-CAT was below 12%. Xross-CAT correlates well with Biophen DiXaI (r_s = 0.885). The bias, determined by Bland-Altman analysis, was 4.9% and the Passing-Bablok equation was y = 1.1x - 2.1. The correlation of plasma levels with TG was moderate (ETP r_s = -0.548; Peak r_s = -0.559), as for the PT (r_s = 0.739) and the dRVVT (r_s = 0.692).

CONCLUSIONS

Xross-CAT shows a good correlation with Biophen DiXaI that was previously confirmed to accurately assess rivaroxaban levels. Bleeding and thrombotic complications are not necessarily associated with drug levels and could be influenced by concomitant risk factors. The main benefit of Xross-CAT is that it can be performed simultaneously with thrombin generation, providing an overview of the global anticoagulation status of a patient in relation to circulating DOAC levels.

International Normalized Ratio as a Screening Test for Assessment of Anticoagulant Activity for Patients Treated With Rivaroxaban or Apixaban: A Pilot Study

Introduction: In patients treated with direct oral anti activated factor X (anti-FXa) anticoagulants such as apixaban and rivaroxaban, there are several emergency and non-emergency conditions in which anticoagulation activity should be measured. The validity of the common global clotting tests, prothrombin time and international normalized ratio (PT/INR) for determination of blood levels of these drugs, has been widely investigated. As the anticoagulation activity evaluation “calibrated anti-FXa” of these drugs is relatively more expensive and less available, we aimed to build a prediction model for anticoagulation activity assessment based on INR values.

Methods and Findings: One hundred sixty samples from 80 hospitalized patients treated with apixaban or rivaroxaban were tested using PT/INR and Anti-FXa chromogenic assay. Two blood samples, trough and peak, were collected from each subject. Participants were randomly divided into two equal groups. One group (n = 40) was used to build the model, which was validated by the second group (n = 40). There was a strong correlation between anti-FXa concentrations and INR in rivaroxaban treated patients (r = 0.899, p < 0.001). Therefore, we were able to build a formula for rivaroxaban patient group which reliably represent the relationship between these two parameters. The correlation in apixaban treated patients was less predictive (r = 0.798, p < 0.001) and the formula suggested could not be validated.

Conclusions: In our study, we developed a formula that estimates the anticoagulant activity of rivaroxaban by obtaining INR values. Where anti-FXa assay is unavailable, our proposed formula may be considered as a screening test for rivaroxaban.

Measurements of endogenous thrombin potential using the CAT method in cats: Reference values and influence of the direct factor Xa inhibitor apixaban

The aim of this study was to establish a thrombin generation assay (calibrated automated thrombogram, CAT) in cats by determining the precision (repeatability), reference values, and the sensitivity to anticoagulant treatment with the factor Xa inhibitor apixaban. The CAT method was performed on citrated plasma with different commercial tissue factor (TF) reagents (PPP Reagent 1 pM [LOW], PPP Reagent 5 pM, PPP Reagent 20 pM [HIGH]) according to the manufacturers` test instruction. Measurements in triplicate were performed in platelet poor plasma (PPP) of 58 healthy cats and in 6 cats at different times following the oral administration of 2.5 mg apixaban. The median CVs in healthy cats usually were < 10% with the exception of thrombin peak height measured using PPP Reagent 1 pM (14.6%). Reference values of all parameters showed marked inter-individual variability and depended largely on the TF concentration of the used activating reagent. Thrombin generation was significantly influenced by apixaban and reacted more sensitively than other tests of haemostasis including the prothrombin time, aPTT, and rotational elastometry. In conclusion, thrombin generation measured by the CAT method using commercially available reagents seems suitable for the examination of feline PPP and may be a valuable method to establish effective anticoagulant therapies for the feline patient and monitoring of such therapies in cats.

Assessment of the analytical performances and sample stability on ST Genesia system using the STG-DrugScreen application

BACKGROUND

Thrombin generation testing has been used to provide information on the coagulation phenotype of patients. The most used technique is the calibrated automated thrombogram (CAT) but it suffers from a lack of standardization, preventing its implementation in routine. The ST Genesia is a new analyzer designed to assess thrombin generation based on the same principle as the CAT. Unlike the CAT system, the ST Genesia is a benchtop, fully automated analyzer, able to perform the analyses individually and not by batch, with strict control of variables such as temperature and volumes, ensuring, theoretically, maximal reproducibility.

OBJECTIVES

This study aimed at assessing the performance of the STG-DrugScreen application on the ST Genesia analyzer. We also aimed at exploring stability of plasma samples after freezing and defining a reference normal range.

RESULTS

Results demonstrated the excellent interexperiment precision of the ST Genesia and confirmed that the use of a reference plasma helps reducing the inter-experiments variability. Stability revealed that plasma samples are stable for at least 11 months at -70°C or lower, except for those containing low molecular weight heparins which have to be tested within 6 months. Freezing had no effect on the majority of thrombin generation parameters except on time to peak.

CONCLUSIONS

Our results suggest an easy implementation of thrombin generation with the use of ST Genesia in the routine laboratory. This will facilitate the design of multicentric studies and enable the establishment of reliable and evidence-based thresholds, which may improve the management of patients treated with anticoagulants.

Patients on NOACs in the Emergency Room

PURPOSE OF REVIEW

Despite the increasing use of NOACs, there is still uncertainty on how to treat NOAC patients presenting with neurological emergencies. Initial assessment of coagulation status is challenging but essential in these patients to provide best-possible treatment in case of ischemic or hemorrhagic stroke. Meanwhile, anticoagulation reversal strategies have been suggested; yet, the optimal management is still unestablished. The current review aims to provide up-to-date information on (i) how to identify patients with NOAC intake, (ii) which therapies are feasible in the setting of ischemic and hemorrhagic stroke as well as traumatic intracranial hemorrhage, and (iii) how to proceed with patients requiring emergency lumbar puncture.

RECENT FINDINGS

Despite several expert opinions, there is still an ongoing debate which NOAC patients presenting with ischemic stroke may benefit from recanalizing strategies and whether these treatment approaches can be performed safely. Results from two phase IV trials investigating the efficacy of NOAC-specific reversal agents in case of major bleeding seem promising with regard to hemostatic parameters, but these antidotes have not been verified to clinically benefit patients, and approval by authorities in parts is still pending. Specific reversal agents are on the way and will provide new treatment options in patients with NOAC-related ischemic and hemorrhagic stroke. Up to now, the decision which patients should undergo recanalizing treatment for ischemic stroke, or which specific pharmacological reversal treatment in hemorrhagic stroke should be initiated, has to be made cautiously on an individual basis after assessing hemostatic parameters.

Therapeutic monitoring of rivaroxaban in dogs using thromboelastography and prothrombin time

BACKGROUND

The chromogenic anti-Xa assay, the gold standard for monitoring the anti-Xa effect of rivaroxaban, is not available as a cage-side diagnostic test for use in a clinical setting.

HYPOTHESIS/OBJECTIVES

To evaluate clinical modalities for measuring the anticoagulant effects of rivaroxaban using a point-of-care prothrombin time (PT) and thromboelastography (TEG).

ANIMALS

Six healthy Beagle dogs.

METHODS

Prospective, experimental study. Four different doses of rivaroxaban (0.5, 1, 2, and 4 mg/kg) were administered PO to dogs. Single PO and 3 consecutive dosing regimens also were assessed. Plasma rivaroxaban concentration was determined using a chromogenic anti-Xa assay, point-of-care PT, and TEG analysis with 4 activators (RapidTEG, 1 : 100 tissue factor [TF100], 1 : 3700 tissue factor [TF3700], and kaolin), and results were compared. Spearman correlation coefficients were calculated between ratios (peak to baseline PT; peak reaction time [R] of TEG to baseline [R] of TEG) and anti-Xa concentration.

RESULTS

Anti-Xa concentration had a significant correlation with point-of-care PT (R = 0.82, P < .001) and RapidTEG-TEG, TF100-TEG, and TF3700-TEG (R = 0.76, P < .001; R = 0.82, P < .001; and R = 0.83, P < .001, respectively).

CONCLUSIONS AND CLINICAL IMPORTANCE

Overall, a 1.5-1.9 × delay in PT and R values of TEG 3 hours after rivaroxaban administration is required to achieve therapeutic anti-Xa concentrations of rivaroxaban in canine plasma. The R values of TEG, specifically using tissue factors (RapidTEG, TF100, TF3700) and point-of-care PT for rivaroxaban can be used practically for therapeutic monitoring of rivaroxaban in dogs.

Accidental Rivaroxaban Intoxication in a Boy: Some Lessons in Managing New Oral Anticoagulants in Children

Novel oral anticoagulants offer equivalent or improved therapeutic profiles compared with warfarin, with less risk of bleeding, no interactions with food, and no need for routine laboratory monitoring. Caution must be exercised in using these drugs in certain patient populations, for example, renal insufficiency, those receiving additional antithrombotic therapy, those with questionable compliance, children, and those with a high risk of gastrointestinal bleeding. One of the novel oral anticoagulants, rivaroxaban, is a direct Factor Xa inhibitor, used to reduce risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation, deep vein thrombosis, and pulmonary embolism. We report a child who presented abnormal coagulation tests after unintended ingestion of 4 tablets of rivaroxaban. The patient was treated with fresh frozen plasma as well as admitted to intensive care and improved several hours later. We discuss his presentation and review of the literature on this topic.