Laboratory assessment of rivaroxaban: a review

ABCG2 polymorphism and rivaroxaban pharmacokinetics in healthy individuals after a single dose

Rivaroxaban is a direct factor Xa inhibitor. Its interindividual variability is large and may be connected to the occurrence of adverse drug reactions or drug inefficacy. Pharmacogenetics studies concentrating on the reasons underlying rivaroxaban's inadequate response could help explain the differences in treatment results and medication safety profiles. Against this background, this study evaluated whether polymorphisms in the gene encoding the ABCG2 transporter modify the pharmacokinetic characteristics of rivaroxaban. A total of 117 healthy volunteers participated in two bioequivalence experiments with a single oral dose of 20 mg rivaroxaban, with one group fasting and the other being fed. Ultra-high-performance liquid chromatography coupled with mass spectrometry was employed to determine the plasma concentrations of rivaroxaban, and the WinNonlin program was used to calculate the pharmacokinetics parameters. In the fasting group, the rivaroxaban pharmacokinetic parameters of Vd (508.27 vs 334.45 vs 275.59 L) and t1/2 (41.04 vs 16.43 vs 15.47 h) were significantly higher in ABCG2 421 A/A genotype carriers than in ABCG2 421 C/C and 421 C/A genotype carriers (P<0.05). The mean values of Cmax (145.81 vs 176.27 vs 190.19 ng/mL), AUC0-t (1193.81 vs 1374.69 vs 1570.77 ng/mL·h), and Cl (11.82 vs 14.50 vs 13.01 mL/h) for these groups were lower, but this difference was not statistically significant (P>0.05). These findings suggested that the ABCG2 421 A/A genotype may impact rivaroxaban parameters after a single dose in healthy subjects. This finding must be validated before it is applied in clinical practice.

Calibration-free electrochemical sensor to monitor factor-Xa inhibitors at the point-of-care anticoagulation therapy

This article presents a novel proof of concept for the blood plasma quantification of clinically relevant concentrations of direct oral anticoagulants, DOACs, including rivaroxaban and edoxaban, as well as low-molecular-weight heparins, LMWHs, such as enoxaparin and dalteparin, utilising a calibration-free disposable electrochemical sensor with co-facing electrodes. A dose-response curve was generated for rivaroxaban and edoxaban to demonstrate the sensor's ability to detect ≥9.00 ng mL-1 rivaroxaban and quantify it in the 11.0-140 ng mL-1 range. Similarly, the lower detection limit for edoxaban was 12.9 ng mL-1, with a quantification range of 16.8-140 ng mL-1. The significance of this sensor lies in its ability to quantify rivaroxaban and edoxaban below 30 ng mL-1, which is crucial in emergency care centres when patients undergoing DOAC therapy require emergency surgery or reversal of DOACs due to bleeding or ischemic stroke. Furthermore, the sensor can detect ≥0.016 IU mL-1 enoxaparin and ≥0.013 IU mL-1 dalteparin and quantify them in the 0.025-0.75 and 0.019-0.75 IU mL-1 range, respectively. Additionally, a dose-response curve was presented to demonstrate the potential ability of this sensor to quantify factor-Xa inhibitors independently of which DOACs or LMWHs are used. With the assay completed in less than 30 s using a minimal volume of 7 μL sample, the possibility to work at physiological pH and under calibration-free format makes this assay an excellent candidate for point-of-care testing.

Magnetic coagulometry: towards a new nanotechnological tool for ex vivo monitoring coagulation in human whole blood

Blood clotting disorders consisting of unwanted blood clot formation or excessive bleeding are some of the main causes of death worldwide. However, there are significant limitations in the current methods used to clinically monitor the dynamics of clot formation in human whole blood ex vivo. Here a new magnetic coagulometry platform for testing ex vivo coagulation is described. This platform exploits the sensitivity of the out-of-phase component of alternating current (AC) magnetic susceptibility (χ'') to variations in mobility and agglomeration of magnetic nanoparticles when trapped during blood clot formation. By labelling human whole blood with magnetic nanoparticles, the out-of-phase component of AC magnetic susceptibility shows that the dynamics of blood clot formation correlates with a decrease in the out-of-phase component χ'' over time activation of coagulation. This is caused by a rapid immobilisation of nanoparticles upon blood coagulation and compaction. In contrast, this rapid fall in the out-of-phase component χ'' is significantly slowed down when blood is pre-treated with three different anticoagulant drugs. Remarkably, the system showed sensitivity towards the effect of clinically used direct oral anticoagulation (DOAC) drugs in whole blood coagulation, in contrast to the inability of clinical routine tests prothrombin time (PT) and partial thromboplastin time (PTT) to efficiently monitor this effect. Translation of this nanomagnetic approach into clinic can provide a superior method for monitoring blood coagulation and improve the efficiency of the current diagnostic techniques.

Pharmacokinetics and pharmacodynamics of direct oral anticoagulants

INTRODUCTION

Direct oral anticoagulants (DOACs) have overtaken vitamin K antagonists to become the most widely used method of anticoagulation for most indications. Their stable and predictable pharmacokinetics combined with relatively simple dosing, and the absence of routine monitoring has made them an attractive proposition for healthcare providers. Despite the benefits of DOACs as a class, important differences exist between individual DOAC drugs in respect of their pharmacokinetic and pharmacodynamic profiles with implications for dosing and reversal in cases of major bleeding.

AREAS COVERED

This review summarizes the state of knowledge relating to the pharmacokinetics of dabigatran (factor IIa/thrombin inhibitor) and apixaban, edoxaban and rivaroxaban (factor Xa) inhibitors. We focus on pharmacokinetic differences between the drugs which may have clinically significant implications.

EXPERT OPINION

Patient-centered care necessitates a careful consideration of the pharmacokinetic and pharmacodynamic differences between DOACs, and how these relate to individual patient circumstances. Prescribers should be aware of the potential for pharmacokinetic drug interactions with DOACs which may influence prescribing decisions in patients with multiple comorbidities. In order to give an appropriate dose of DOAC drugs, accurate estimation of renal function using the Cockcroft-Gault formula using actual body weight is necessary. An increasing body of evidence supports the use of DOACs in patients who are obese, and this is becoming more routine in clinical practice.

In vitro evaluation of anticoagulant therapy management when urgent percutaneous coronary intervention is required in rivaroxaban-treated patients

We investigated in vitro the management of intraprocedural anticoagulation in patients requiring immediate percutaneous coronary intervention (PCI) while using regular direct oral anticoagulants (DOACs). Twenty-five patients taking 20 mg of rivaroxaban once daily comprised the study group, while five healthy volunteers included the control group. In the study group, a beginning (24 h after the last rivaroxaban dose) examination was performed. Then, the effects of basal and four different anticoagulant doses (50 IU/kg unfractionated heparin (UFH), 100 IU/kg UFH, 0.5 mg/kg enoxaparin, and 1 mg/kg enoxaparin) on coagulation parameters were investigated at the 4th and 12th h following rivaroxaban intake. The effects of four different anticoagulant doses were evaluated in the control group. The anticoagulant activity was assessed mainly by anti-factor Xa (anti-Xa) levels. Beginning anti-Xa levels were significantly higher in the study group than in the control group (0.69 ± 0.77 IU/mL vs. 0.20 ± 0.14 IU/mL; p < 0.05). The study group's 4th and 12th-h anti-Xa levels were significantly higher than the beginning level (1.96 ± 1.35 IU/mL vs. 0.69 ± 0.77 IU/mL; p < 0.001 and 0.94 ± 1.21 IU/mL vs. 0.69 ± 0.77 IU/mL; p < 0.05, respectively). Anti-Xa levels increased significantly in the study group with the addition of UFH and enoxaparin doses at the 4th and 12th h than the beginning (p < 0.001 at all doses). The safest anti-Xa level (from 0.94 ± 1.21 to 2.00 ± 1.02 IU/mL) was achieved 12 h after rivaroxaban with 0.5 mg/kg enoxaparin. Anticoagulant activity was sufficient for urgent PCI at the 4th h after rivaroxaban treatment, and additional anticoagulant administration may not be required at this time. Twelve hours after taking rivaroxaban, administering 0.5 mg/kg of enoxaparin may provide adequate and safe anticoagulant activity for immediate PCI. This experimental study result should confirm with clinical trials (NCT05541757).

Real-world decision-making in the management of patients presenting with major bleeding on rivaroxaban: the Auckland regional experience

BACKGROUND

Rivaroxaban is used increasingly as an oral anticoagulant; however, a specific reversal agent is not currently available in the Australasian setting. There is also variation across international consensus guidelines regarding advice on the management of bleeding.

AIMS

To review the real-world management of rivaroxaban-associated major bleeding across the public hospitals of New Zealand's largest city.

METHODS

A retrospective cohort analysis was performed of patients prescribed rivaroxaban who presented to four metropolitan hospital Emergency Departments between 1 August 2018 and 31 May 2021 with major bleeding as defined by the International Society on Thrombosis and Haemostasis.

RESULTS

One hundred and twelve patients were identified, accounting for 115 major bleeding presentations. Upper gastrointestinal (34%) and intracranial (31%) bleeding sites were most common. Procedural intervention was required in 44% of patients. Haemostatic management involved tranexamic acid (TXA) in 26%, prothrombin complex concentrate (PCC) in 55% (dose range 1000-6000 IU or 10-65 IU/kg), vitamin K in 16% and fresh frozen plasma in 1%. Rivaroxaban was discontinued permanently following 56 (49%) events, switched to another anticoagulant in 24 (21%) and withheld in 30 (26%) from 2 days to 3 months (median 8.5 days). All-cause mortality at 90 days after bleeding was 17% (19 patients), and the incidence of combined venous and arterial thrombotic events was 10%.

CONCLUSIONS

There is considerable heterogeneity in the acute clinical management of patients presenting with rivaroxaban-related major bleeding. The use of PCC and dosage administered is inconsistent. TXA was utilised in only approximately one-quarter of all cases. Evidence-based guidance for treating rivaroxaban-related bleeding would improve the management of these patients and potentially improve clinical outcomes.

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

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

Comparison of the efficacy and safety of rivaroxaban and low-molecular-weight heparin in Chinese lung cancer patients with nonhigh-risk pulmonary embolism

BACKGROUND

Data that guide selection of differing anticoagulant regimens for specific cancer-associated venous thromboembolism (VTE) are lacking. We aimed to compare the efficacy and safety of rivaroxaban and low-molecular-weight heparin (LMWH) against nonhigh-risk pulmonary embolism (PE) in Chinese lung cancer patients.

METHODS

Four hundred forty-six Chinese lung cancer patients with nonhigh-risk PE who initiated treatment with rivaroxaban or LMWH were identified from Zhongshan Hospital database from 2016 to 2020. The primary outcomes were the composite event of VTE recurrence or major bleeding, and all-cause mortality. The secondary outcomes were VTE recurrence, major bleeding and clinically relevant non-major bleeding (CRNMB). Propensity score matching was used to balance baseline covariates. We conducted sensitivity analysis by stabilized inverse probability of treatment weighting and competing risk analysis by a Fine and Gray subdistribution hazard model.

RESULTS

In propensity score-matched cohorts, rivaroxaban was similar to LMWH in the risks of the composite outcome (hazard ratio (HR), 0.73; 95% confidence interval (CI), 0.45-1.21; P = 0.22), VTE recurrence (HR, 0.69; 95% CI, 0.36-1.34; P = 0.28), major bleeding (HR, 0.79; 95% CI, 0.37-1.68; P = 0.54) and CRNMB (HR, 1.13; 95% CI, 0.62-2.09; P = 0.69). All-cause mortality was significantly lower in rivaroxaban group than LMWH group (HR, 0.52; 95% CI, 0.36-0.75; P < 0.001). The primary and secondary outcomes favored rivaroxaban over LMWH in all the subgroups expect for central PE and intermediate-risk PE. The sensitivity analysis yielded similar results, and competing risk analysis was in accordance with the primary findings.

CONCLUSIONS

Rivaroxaban might be a promising alternative to LMWH as initial treatment for nonhigh-risk PE in lung cancer patients.

To Measure or Not to Measure: Direct Oral Anticoagulant Laboratory Assay Monitoring in Clinical Practice

The need for therapeutic drug monitoring of direct oral anticoagulants (DOACs) remains an area of clinical equipoise. Although routine monitoring may be unnecessary given predictable pharmacokinetics in most patients, there may be altered pharmacokinetics in those with end organ dysfunction, such as those with renal impairment, or with concomitant interacting medications, at extremes of body weight or age, or in those with thromboembolic events in atypical locations. We aimed to assess real-world practices in situations in which DOAC drug-level monitoring was used at a large academic medical center. A retrospective review of the records of patients who had a DOAC drug-specific activity level checked from 2016 to 2019 was included. A total of 119 patients had 144 DOAC measurements (apixaban (n = 62) and rivaroxaban (n = 57)). Drug-specific calibrated DOAC levels were within an expected therapeutic range for 110 levels(76%), with 21 levels (15%) above the expected range and 13 levels (9%) below the expected range. The DOAC levels were checked in the setting of an urgent or emergent procedure in 28 patients (24%), followed by renal failure in 17 patients (14%), a bleeding event in 11 patients (9%), concern for recurrent thromboembolism in 10 patients (8%), thrombophilia in 9 patients (8%), a history of recurrent thromboembolism in 6 patients (5%), extremes of body weight in 7 patients (5%), and unknown reasons in 7 patients (5%). Clinical decision making was infrequently affected by the DOAC monitoring. Therapeutic drug monitoring with DOACs may help predict bleeding events in elderly patients, those with impaired renal function, and in the event of an emergent or urgent procedure. Future studies are needed to target the select patient-specific scenarios where monitoring DOAC levels may impact clinical outcomes.

Design and Optimization of Rivaroxaban-Cyclodextrin-Polymer Triple Complex Formulation with Improved Solubility

Purpose

This study aimed to ensure the convenience of administration and reproducibility of efficacy, regardless of the meal, by improving the solubility of rivaroxaban (RIV).

Methods

RIV is a non-vitamin K antagonist oral anticoagulants that exhibits a coagulation effect by directly inhibiting coagulation factor Xa. However, RIV has a very low solubility; therefore, it must be administered with a meal at high doses. We used a drug- hydroxypropyl-beta-cyclodextrin (CD)-water-soluble polymer triple complex (R-C-P complex) to solubilize RIV. Using Minitab, we evaluated the effect of each factor on RIV solubility and developed an optimal R-C-P complex formulation. The amount of CD, amount of polymer, and polymer type were set as the independent variables X₁, X₂, and X₃, respectively. RIV solubility (Y₁) and dissolution rate for 45 min in pH 4.5 medium (Y₂) and pH 1.2 medium (Y₃) were set as response variables.

Results

The most efficient RIV solubilization effect was obtained from the composition using CD and HPMC 2208, and physicochemical properties and dissolution parameters were analyzed. RIV in the R-C-P complex was present in an amorphous form and showed high solubility. Unlike commercial products, it showed a 100% dissolution rate. The R-C-P complex formulation secured high RIV solubility and 100% release regardless of pH.

Conclusion

The results imply that high-dose RIV can be administered regardless of the meal, reducing the risk of changing the drug effect due to the patient's administration mistake.

Pyrazole-Based Thrombin Inhibitors with a Serine-Trapping Mechanism of Action: Synthesis and Biological Activity

New antithrombotic drugs are needed to combat thrombosis, a dangerous pathology that causes myocardial infarction and ischemic stroke. In this respect, thrombin (FIIa) represents an important drug target. We herein report the synthesis and biological activity of a series of 1H-pyrazol-5-amine-based thrombin inhibitors with a serine-trapping mechanism of action. Among synthesized compounds, flexible acylated 1H-pyrazol-5-amines 24e, 34a, and 34b were identified as potent 16-80 nM thrombin inhibitors, which showed practically no off-targeting effect against other physiologically relevant serine proteases. To prove that synthesized compounds are covalent thrombin inhibitors, the most potent derivative 24e (FIIa IC₅₀ = 16 nM) was studied in a mass-shift assay, where it has been shown that 24e transfers its acyl moiety (pivaloyl) to the catalytic Ser195 of thrombin. Performed herein docking studies also confirmed the covalent mechanism of thrombin inhibition by synthesized compounds. Acylated aminopyrazoles found during this study showed only limited effects on plasma coagulation in activated partial thrombin time (aPTT) and prothrombin time (PT) in vitro assays. However, such thrombin inhibitors are expected to have virtually no effect on bleeding time and can be used as a starting point for developing a safer alternative to traditional non-covalent anticoagulants.

Population pharmacokinetic and pharmacodynamic analysis of rivaroxaban in Chinese patients with non-valvular atrial fibrillation

Rivaroxaban, a direct factor Xa inhibitor, is widely used for stroke prevention in patients with non-valvular atrial fibrillation (NVAF). The aim of this study was to conduct a population pharmacokinetic-pharmacodynamic (PK-PD) analysis of rivaroxaban in Chinese patients with NVAF to assess ethnic differences and provide model-based precision dosing. A total of 256 rivaroxaban plasma concentrations and 244 prothrombin time (PT) measurements were obtained from 195 Chinese NVAF patients from a prospective clinical trial. The population PK-PD model was developed using nonlinear mixed effects modeling (NONMEM) software. The PK of rivaroxaban was adequately described using a one-compartment model with first-order adsorption and elimination. Estimated glomerular filtration rate (eGFR) was identified as a major covariate for apparent clearance. No single nucleotide polymorphism was identified as a significant covariate. PT exhibited a linear relationship with rivaroxaban concentration. Total bilirubin (TBIL) and eGFR were identified as significant covariates for baseline PT. According to the Monte Carlo simulation, 15 mg for Chinese patients with eGFR ≥50 mL/min and normal liver function yielded an exposure comparable to 20 mg for Caucasian patients. Patients with moderately impaired renal function may require a lower dose of rivaroxaban to avoid overexposure. Moreover, there was an approximate 26% increase in PT levels in patients with TBIL of 34 μmol/L and eGFR of 30 mL/min, which could increase the risk of major bleeding. The established population PK-PD model could inform individualized dosing for Chinese NVAF patients who are administered rivaroxaban.

Clinical features and posttreatment monitoring of dogs administered rivaroxaban (2018-2020): 19 cases

OBJECTIVE

To describe a population of sick dogs administered rivaroxaban monitored with a rivaroxaban-calibrated anti-Xa activity assay (aXa).

DESIGN

Descriptive retrospective study.

SETTING

Two veterinary teaching hospitals.

ANIMALS

Client-owned dogs administered rivaroxaban and monitored with aXa from January 2018 to January 2020 were eligible for study.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Medical records were reviewed and 19 dogs with a variety of underlying disease processes were identified. Rivaroxaban was administered to 12 of 19 dogs (63%) with confirmed thrombosis, 4 of 19 dogs (21%) with a strong clinical suspicion of thrombosis, and in 3 of 19 dogs (16%) with no current evidence of thrombosis. The median rivaroxaban dose administered was 0.96 mg/kg/day (0.62-1.58 mg/kg/day), with 15 of 19 dogs (79%) receiving rivaroxaban once daily. Clopidogrel was concurrently administered to 11 of 19 dogs (58%). Complete or partial thrombus resolution was identified in 5 of 12 (42%) and 3 of 12 (25%) dogs, respectively. Rivaroxaban appeared safe, with only 1 of 19 dogs (5%), concurrently administered clopidogrel, developing evidence of mild hematuria. Posttreatment monitoring revealed that 8 of 19 dogs (42%) had aXa below the target (aXa range of 150-250 ng/ml associated with effective treatment and prevention of venous thrombosis in people). The remaining 3 to 19 dogs (16%) achieved this range, and 8 of 19 dogs (42%) exceeded the range. No significant relationship between the initial rivaroxaban dose administered and the corresponding aXa result was identified. There were also no significant differences in baseline clinicopathological variables in dogs in which aXa fell within or outside this range.

CONCLUSIONS

aXa was most commonly measured in dogs receiving rivaroxaban with confirmed or suspected thrombosis. Dogs in this study received a range of rivaroxaban dosages and attained variable aXa values that were not directly correlated with dosage.

Risk factors associated with post-extraction bleeding in patients on warfarin or direct-acting oral anticoagulants: a retrospective cohort study

PURPOSE

The purpose of this study was to investigate the risk factors associated with post-extraction persistent bleeding in patients on warfarin or direct-acting oral anticoagulants (DOACs) and the ability of risk scores to predict post-extraction bleeding.

METHODS

Three hundred ninety-one patients taking warfarin or DOACs underwent tooth extractions. Various risk factors for post-extraction bleeding, including number of tooth extraction, with antiplatelet therapy, and risk scores, were investigated by univariate and multivariate analyses. A post-extraction bleeding was classified into grades 1-3.

RESULTS

The incidence of post-extraction bleeding was 26.8% (77 out of 287 patients; grade 1: 63, grade 2:14) in patients taking warfarin, and 26.0% (27 out of 104 patients; grade 1: 20, grade 2:7) in patients taking warfarin DOACs. Multivariate analyses showed that multiple teeth extractions and HAS-BLED scores (above 3 points) in patients taking warfarin, and only multiple teeth extractions in patients taking DOAC, were significantly associated with post-extraction bleeding, respectively.

CONCLUSION

Most of the post-extraction bleedings were grade 1, which can be stopped by eligibly pressing gauze by surgeons. If patients taking anticoagulants are scheduled to undergo multiple teeth extractions or their HAS-BLED score are above 3 points (if warfarin), we recommend informing patients risk of post-extraction bleeding before operation, taking carefully hemostasis, and instructing patients to bite down accurately on the gauze for longer than usual.

MicroRNAs as novel biomarkers for rivaroxaban therapeutic drug monitoring

OBJECTIVES

The aim of this study is to assess micro-RNAs miR-142 and miR-39 as potential biomarkers for drug-monitoring of rivaroxaban among elderly patients with atrial fibrillation.

METHODS

The study involved 57 patients with median (ME) age 87 years [80-94 years old] with nonvalvular atrial fibrillation admitted to a multidisciplinary hospital in Moscow. High-performance liquid chromatography with mass-spectrometry detection (HPLC-MS) was carried out to measure rivaroxaban concentrations. Carriership of CYP3A4 and ABCB1 was detected. MiRNA expression levels were measured. The activity of CYP3A4 isoenzyme was measured as the ratio of the concentrations of 6β-hydroxycortisol and cortisol.

RESULTS

The miR-142 expression levels of patients with CC allelic variant polymorphism ABCB1 3435 C>T (rs1045642) were significantly higher compared to CT and TT variants 31.69 ± 1.60 vs. 34.06 ± 1.66 vs. 33.16 ± 1.77 (p=0.021). Carriers of TT allelic variant polymorphism ABCB1 rs4148738 had a higher concentration of the 6-beta-hydroxycortisol in urine compared to CC and CT variants 3,467.35 ± 1,055.53 vs. 3,453.52 ± 1,516.89 vs. 2,593.30 ± 1,172.52 (p=0.029). As for CYP3A4*22, the carriers of CC allelic variant had higher prothrombin time 14.10 ± 2.17 vs. 11.87 ± 0.60 and INR 1.31 ± 0.20 vs. 1.1 ± 0.06 but lower Quick's value 74.52 ± 16.84 vs. 97.55 ± 10.54 (p=0.059). A positive correlation between the Ct miR-142 and the aPTT p=0.019 was noted. Also miR-142 has a correlation with Quick's value p=0.095. There is no statistically significant connection between miR-142 and miR-39 expression levels and the plasma concentration of rivaroxaban (b coefficient=-2.055, SE 3.952, p=0.605 and b coefficient=1.546, SE 9.887, p=0.876 in the linear regression model respectively).

CONCLUSIONS

This study has assessed new potential biomarkers for rivaroxaban therapeutic drug monitoring: miR-142 and miR-39.

MicroRNAs as novel biomarkers for rivaroxaban therapeutic drug monitoring

OBJECTIVES

The aim of this study is to assess micro-RNAs miR-142 and miR-39 as potential biomarkers for drug-monitoring of rivaroxaban among elderly patients with atrial fibrillation.

METHODS

The study involved 57 patients with median (ME) age 87 years [80-94 years old] with nonvalvular atrial fibrillation admitted to a multidisciplinary hospital in Moscow. High-performance liquid chromatography with mass-spectrometry detection (HPLC-MS) was carried out to measure rivaroxaban concentrations. Carriership of CYP3A4 and ABCB1 was detected. MiRNA expression levels were measured. The activity of CYP3A4 isoenzyme was measured as the ratio of the concentrations of 6β-hydroxycortisol and cortisol.

RESULTS

The miR-142 expression levels of patients with CC allelic variant polymorphism ABCB1 3435 C>T (rs1045642) were significantly higher compared to CT and TT variants 31.69 ± 1.60 vs. 34.06 ± 1.66 vs. 33.16 ± 1.77 (p=0.021). Carriers of TT allelic variant polymorphism ABCB1 rs4148738 had a higher concentration of the 6-beta-hydroxycortisol in urine compared to CC and CT variants 3,467.35 ± 1,055.53 vs. 3,453.52 ± 1,516.89 vs. 2,593.30 ± 1,172.52 (p=0.029). As for CYP3A4*22, the carriers of CC allelic variant had higher prothrombin time 14.10 ± 2.17 vs. 11.87 ± 0.60 and INR 1.31 ± 0.20 vs. 1.1 ± 0.06 but lower Quick's value 74.52 ± 16.84 vs. 97.55 ± 10.54 (p=0.059). A positive correlation between the Ct miR-142 and the aPTT p=0.019 was noted. Also miR-142 has a correlation with Quick's value p=0.095. There is no statistically significant connection between miR-142 and miR-39 expression levels and the plasma concentration of rivaroxaban (b coefficient=-2.055, SE 3.952, p=0.605 and b coefficient=1.546, SE 9.887, p=0.876 in the linear regression model respectively).

CONCLUSIONS

This study has assessed new potential biomarkers for rivaroxaban therapeutic drug monitoring: miR-142 and miR-39.

Andexanet Alfa Use for Small Bowel Obstruction Patient With History of Sugiura Procedure

This case report is about a 51-year-old active duty male with JAK2 mutation and medical history significant for prehepatic portal hypertension from portal vein thrombus on lifelong anticoagulation with rivaroxaban, an oral factor Xa inhibitor, presenting with closed-loop small bowel obstruction requiring emergent laparotomy. We present this surgical case as it required emergent reversal of the oral factor Xa inhibitor with andexanet alfa.

Hemopericardium with subsequent cardiac tamponade secondary to rivaroxaban treatment: a case report

Background

The use and utility of novel oral anticoagulants has been increasing in clinical practice due to their relatively lower incidence of side effects such as intracranial haemorrhage, particularly in the elderly, when compared with vitamin K antagonists. Rivaroxaban is a factor Xa and prothrombinase inhibitor indicated for stroke and venous thromboembolism prophylaxis in non-valvular atrial fibrillation as well as treatment of venous thromboembolism.

Case summary

A patient with history of paroxysmal atrial fibrillation on Rivaroxaban presented with generalized malaise, lightheadedness, and dizziness. The patient was found to be in profound cardiogenic shock despite unremarkable cardiac enzymes. Electrocardiogram revealed rate controlled atrial fibrillation and T-wave inversions in the inferolateral leads without associated electrical alternans. Bedside echocardiogram revealed a large pericardial effusion consistent with cardiac tamponade physiology. Following anticoagulation reversal, the patient underwent urgent pericardiocentesis yielding haemorrhagic fluid, with subsequent improvement in haemodynamic status. Despite the presence of retroperitoneal lymphadenopathy on previous computed tomography of the abdomen and concern for underlying malignant effusion secondary to lymphoma, cytology of the fluid revealed no evidence of malignant cells and follow-up flow cytometry and bone marrow biopsy were unremarkable.

Discussion

While hemopericardium is not listed as a known side effect of Rivaroxaban, previous cases of hemopericardium secondary to Rivaroxaban have been described in the literature secondary to pre-disposing risk factors including CYP450 drug interactions or cardiac device implantations. In this case, the patient experienced a spontaneous hemopericardium on Rivaroxaban without any previously elucidated risk factors or evidence of malignancy.

Effect of myeloperoxidase on the anticoagulant activity of low molecular weight heparin and rivaroxaban in an in vitro tumor model

BACKGROUND

Inflammation with leukocyte activation is a hallmark of cancer-associated thrombosis (CAT), and elevated leukocytes predict venous thromboembolism in cancer outpatients. In a recent trial, rivaroxaban was more efficacious than dalteparin in preventing CAT recurrence.

OBJECTIVES

In a proof-of-concept study, we aimed to provide a mechanistic basis for improved efficacy of rivaroxaban compared to low molecular weight heparin in CAT treatment.

METHODS

We studied the effects of rivaroxaban, dalteparin, and tinzaparin at peak and trough levels on tumor cell-induced procoagulant activity and platelet aggregation in the presence or absence of the cationic leukocyte-derived enzyme, myeloperoxidase (MPO). Furthermore, pro-inflammatory conditions were generated by stimulating whole blood with lipopolysaccharide (LPS) or phorbol-myristate-acetate (PMA), before measuring thrombin generation in plasma supernatants.

RESULTS

All three anticoagulants inhibited thrombin generation, fibrin clot formation, and platelet aggregation induced by the tissue factor-expressing prostate carcinoma cell line, 22Rv1. Pre-incubation with MPO partially attenuated the anticoagulant activity of dalteparin and tinzaparin, but not rivaroxaban, at trough levels. The effect of MPO did not involve the enzyme's catalytic properties, but required its structural integrity, as indicated by heat denaturation. In plasma obtained from LPS- or PMA-stimulated whole blood, elevated MPO antigen levels inversely correlated with the ability of tinzaparin to inhibit 22Rv1-induced thrombin generation.

CONCLUSIONS

Myeloperoxidase release may partially attenuate the anticoagulant activity of trough levels of dalteparin and tinzaparin in the context of paraneoplastic leukocyte activation. However, this effect is likely not sufficient to explain the improved efficacy of rivaroxaban, and possibly other oral factor Xa inhibitors, in CAT treatment.

Evaluation of point-of-care coagulation tests as alternatives to anti-Xa activity for monitoring the anticoagulant effects of rivaroxaban in healthy dogs

OBJECTIVE

To evaluate a panel of coagulation assays for their potential utility in rivaroxaban monitoring as alternatives to the rivaroxaban-specific anti-Xa activity (RIVA).

DESIGN

Prospective experimental study.

SETTING

University research laboratory.

ANIMALS

Five healthy neutered male Beagles.

INTERVENTIONS

Dogs were administered a median dose of 1.8 mg/kg rivaroxaban (range, 1.6-1.8 mg/kg) orally once daily for 2 consecutive days as part of a pharmacodynamic study. Blood was collected from a preplaced jugular catheter at time points relative to their rivaroxaban administration (0, 2, 4, 8, 24, 36, and 48 h) for measurement of RIVA, prothrombin time (PT), activated partial thromboplastin time, RapidTEG, and thrombin generation variables.

MEASUREMENTS AND MAIN RESULTS

One hundred forty data points were available for analysis. There was poor correlation between RIVA and RapidTEG variables: R time (R) (min) (r = 0.554, P < 0.0001), K time (K) (min) (r = -0.204, P = 0.016), alpha angle (degrees) (r = 0.152, P = 0.073), Maximum amplitude (MA) (mm) (r = 0.106, P = 0.215), and G value (G) (dynes/s) (r = 0.108, P = 0.205). A good correlation was noted between thrombin generation variables and RIVA: lag time (min) (r = 0.827, P < 0.0001), peak (nM) (r = -0.752, P < 0.0001), and endogenous thrombin potential (nM·min) (r = -0.762, P < 0.0001). There was an excellent correlation between PT and RIVA (r = 0.915, P < 0.0001) and a good correlation between activated partial thromboplastin time and RIVA (r = 0.772, P < 0 .0001).

CONCLUSIONS

Of all the coagulation tests investigated, the PT correlated best with RIVA. There is potential for PT being a convenient second-line monitoring option in dogs receiving rivaroxaban, but further work is necessary to validate other PT assays. Thromboelastography performed with strong activators correlated poorly with anti-Xa activity.

The influence of feeding and gastroprotectant medications on the Factor Xa inhibitory activity of orally administered rivaroxaban in normal dogs

OBJECTIVE

Rivaroxaban is a new anticoagulant option for dogs, yet its reported oral bioavailability is as low as 60%. The objective of this study was to examine the influence of feeding and gastroprotectant medications on the bioactivity (anti-Xa activity) of rivaroxaban in healthy dogs.

DESIGN

Prospective experimental study.

SETTING

University research laboratory.

ANIMALS

Five healthy neutered male purpose-bred Beagles.

INTERVENTIONS

Dogs were administered a median dose of 1.8 mg/kg rivaroxaban (range, 1.6-1.8 mg/kg) orally once daily for 2 consecutive days with either (1) no food, (2) food, (3) sucralfate 30 minutes before rivaroxaban, or (4) omeprazole at the same time as rivaroxaban. Blood was collected from preplaced jugular catheters immediately before and at 6 time points after rivaroxaban administration (2, 4, 8, 24, 36, and 48 hours). A rivaroxaban calibrated anti-Xa activity assay (RIVA) was used to monitor anticoagulant effect.

MEASUREMENTS AND MAIN RESULTS

Rivaroxaban administration resulted in significant increases in RIVA (P = 0.02), with peak activities occurring 2 to 4 hours after dosingduring each study arm. No feeding was associated with significantly higher RIVA at the 36-hour time point compared to all other treatment arms (P < 0.0001), and feeding resulted in high RIVA at the 48-hour time point compared with sucralfate administration (P = 0.003). No significant changes in RIVA were otherwise identified with respect to feeding or gastroprotectant administration (P = 0.2).

CONCLUSIONS AND CLINICAL IMPORTANCE

Although administration without food demonstrated an apparent increase in RIVA 36 hours after drug administration, clinically relevant differences among treatment groups were not identified in combined analyses of time points. Based on these results, dogs treated with rivaroxaban do not require special modification of feeding practices or gastroprotectant drug administration.

Life-Threatening Hemoptysis

Life-threatening hemoptysis (LTH) is any amount of hemoptysis that causes significant hemodynamic decompensation or respiratory distress which may lead to death if left untreated. While the amount of hemoptysis that qualifies as massive hemoptysis has continued to be debated, any amount between 100 to 1,000 mL/day is considered significant. Up to 15% cases of hemoptysis are LTH and need urgent life-saving intervention. Understanding of pulmonary vascular anatomy is of paramount importance to manage LTH. The goal of treatment lies in airway protection, appropriate oxygenation, and prevention of exsanguination. Once the airway is stabilized, a quick diagnosis and control of bleeding site is targeted. This chapter highlights current practices and approach to LTH including medical management, bronchoscopic approach, and advanced therapies such as bronchial artery embolization and surgical resection. We review situations, such as bronchiectasis, vascular malformation, diffuse alveolar hemorrhage, and tracheostomy bleed and specific approach to management of these conditions in a systematic and evidence-based manner.

Aspirin and low-dose rivaroxaban - the dual pathway concept in patients with stable atherosclerotic disease: a comprehensive review

INTRODUCTION

Cardiovascular disease is the leading cause of morbidity and mortality in adults in western nations. In the last decades, tremendous research has been conducted in the field of secondary prevention in order to reduce recurrent cardiovascular events. This review summarizes the novel dual pathway concept of aspirin and very low-dose rivaroxaban, from mechanisms to clinical practice.

AREAS COVERED

The COMPASS trial demonstrated that in patients with stable atherosclerotic disease, very low-dose rivaroxaban, a direct factor Xa inhibitor, when combined with aspirin, reduced the rate of recurrent ischemic events, at the cost of increased bleeding. This effect was present in patients with ischemic heart disease, as well as in patients with atherosclerosis in other beds, such as in peripheral arterial disease. Sub-studies from the COMPASS trial examined other high-risk populations who might benefit the most from this regimen.

EXPERT OPINION

There are currently multiple antiplatelet and anticoagulation treatment regimens for patients with stable atherosclerotic disease. The dual pathway concept is a novel approach that combines both mechanisms. Identifying patients who might benefit the most in terms of ischemic events at the least bleeding events still remains a challenge, yet prescribing this combination to high-risk patients might be the most effective.

Tissue factor in atherosclerosis and atherothrombosis

Atherosclerosis is a chronic inflammatory disease that is characterized by the formation of lipid rich plaques in the wall of medium to large sized arteries. Atherothrombosis represents the terminal manifestation of this pathology in which atherosclerotic plaque rupture or erosion triggers the formation of occlusive thrombi. Occlusion of arteries and resultant tissue ischemia in the heart and brain causes myocardial infarction and stroke, respectively. Tissue factor (TF) is the receptor for the coagulation protease factor VIIa, and formation of the TF:factor VIIa complex triggers blood coagulation. TF is expressed at high levels in atherosclerotic plaques by both macrophage-derived foam cells and vascular smooth muscle cells, as well as extracellular vesicles derived from these cells. Importantly, TF mediated activation of coagulation is critically important for arterial thrombosis in the setting of atherosclerotic disease. The major endogenous inhibitor of the TF:factor VIIa complex is TF pathway inhibitor 1 (TFPI-1), which is also present in atherosclerotic plaques. In mouse models, increased or decreased expression of TFPI-1 has been found to alter atherosclerosis. This review highlights the contribution of TF-dependent activation of coagulation to atherthrombotic disease.

Can an anti-Xa assay for unfractionated heparin be used to assess the presence of rivaroxaban in critical situations?

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.

Standard coagulation assays alone are not sufficient to exclude surgically relevant rivaroxaban plasma concentrations

Background

While mainly larger hospitals have introduced routine anti-Xa assays for rivaroxaban (RXA), these are not readily available to smaller hospitals often relying on routine coagulation tests such as prothrombin time (PT) and activated partial thromboplastin time (aPTT).

The aim of our study was to investigate the effect of RXA plasma concentration on the standard coagulation tests PT (Quick test and INR) and aPTT in a large group of real-life patients. We further assessed whether normal results of these standard coagulation assays are sufficient to exclude surgically relevant RXA plasma concentration, defined as > 50 mcg/l.

Methods

This retrospective study included all patients between 2012 and 2016 where anti-Xa (calibrated for RXA), PT (Quick test and INR), and/or aPTT were determined from the same sample. PT is expressed as Quick value (% of normal plasma pool). In total, 1027 measurements in 622 patients were eligible for analysis: 752 measurements of 505 patients for Quick/INR and 594 measurements of 417 patients for aPTT.

Results

A moderate correlation of PT/Quick (Pearson's correlation coefficient − 0.59; p < 0.001), INR (Pearson's correlation coefficient 0.5; p < 0.001), and aPTT (Pearson's correlation coefficient 0.53; p < 0.001) with RXA plasma concentration was observed. However, in 50% of all samples with a normal PT/Quick, in 25% of all samples with a normal INR and in 80% of all samples with a normal aPTT residual RXA plasma concentration was surgically relevant.

Conclusion

Although a moderate correlation of RXA plasma concentration with PT/Quick, INR, and aPTT was observed, standard coagulation assays are not sufficient to exclude surgically relevant RXA plasma concentrations.

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.

Influence of model-predicted rivaroxaban exposure and patient characteristics on efficacy and safety outcomes in patients with acute coronary syndrome

Background:

This analysis aimed to evaluate the impact of rivaroxaban exposure and patient characteristics on efficacy and safety outcomes in patients with acute coronary syndrome (ACS) and to determine whether therapeutic drug monitoring might provide additional information regarding rivaroxaban dose, beyond what patient characteristics provide.

Methods:

A post hoc exposure–response analysis was conducted using data from the phase III ATLAS ACS 2 Thrombolysis in Myocardial Infarction (TIMI) 51 study, in which 15,526 randomized ACS patients received rivaroxaban (2.5 mg or 5 mg twice daily) or placebo for a mean of 13 months (maximum follow up: 31 months). A multivariate Cox model was used to correlate individual predicted rivaroxaban exposures and patient characteristics with time-to-event clinical outcomes.

Results:

For the incidence of myocardial infarction (MI), ischemic stroke, or nonhemorrhagic cardiovascular death, hazard ratios (HRs) for steady-state maximum plasma concentration (C_max) in the 5th and 95th percentiles versus the median were statistically significant but close to 1 for both rivaroxaban doses. For TIMI major bleeding events, a statistically significant association was observed with C_max [HR, 1.08; 95% CI, 1.06–1.11 (95th percentile versus median, 2.5 mg twice daily)], sex [HR, 0.56; 95% CI, 0.38–0.84 (female versus male)], and previous revascularization [HR, 0.62; 95% CI, 0.44–0.87 (no versus yes)].

Conclusions:

The shallow slopes of the exposure–response relationships and the lack of a clear therapeutic window render it unlikely that therapeutic drug monitoring in patients with ACS would provide additional information regarding rivaroxaban dose beyond that provided by patient characteristics.

An assay to measure levels of factor Xa inhibitors in blood and plasma

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.

Micellar liquid chromatography determination of rivaroxaban in plasma and urine. Validation and theoretical aspects

A Micellar Chromatographic method to determine rivaroxaban in plasma and urine has been developed. The samples were dissolved in the mobile phase (SDS 0.05 M - 1-propanol 12.5%, phosphate buffered at pH 7) and 20 μL directly injected, avoiding the extraction and purification steps. Using a C18 column and running under isocratic mode at 1 mL/min, analyte was eluted without interference from the matrix in <6.0 min. The detection absorbance wavelength was set to 250 nm. The procedure was validated by Food and Drug Administration guidelines in terms of: system suitability, calibration range (0.05-5 mg/L), linearity, sensitivity, robustness, carry-over effect, specificity, accuracy (-11.1 to 4.2%), precision (<19.9%), stability and analysis of incurred samples. The method was found reliable, practical, easy-to-conduct, rapid, relatively eco-friendly, safe, inexpensive, widely available and with a high sample throughput. The method was applied to the analysis of incurred samples, including incurred sample reanalysis, to verify that the instrumentation works correctly. In addition, the constants of the different partition equilibria occurring in the column were elucidated in order to have a better comprehension of the theoretical aspects of the retention mechanism. A moderately strong association between rivaroxaban and the stationary phase and the micelles was found, weakened by short chain alcohol.

Diagnostic accuracy of thromboelastometry and its correlation with the HPLC-MS/MS quantification test

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.

Prospective randomized comparative study on rivaroxaban and LMWH for prophylaxis of post-apheresis thrombosis in adoptive T cell immunotherapy cancer patients

Autologous adoptive T cell immunotherapy has been recognized as an effective treatment for cancer patients. The initial qualified lymphocytes is the core element determining the immunotherapeutic outcomes clinically. Cell separator based apheresis procedure is an optimal procedure to collect adequate mono-nucleated lymphocytes to generate efficient ex vivo T cell expansions; however, potential catheter-associated femoral vein thrombosis at post-apheresis might rise an additional deteriorated morbidity for cancer patients. The emerging prophylactic medications are required at such circumstances. Therefore this study was designed to compare the prophylactic effects of rivaroxaban versus low molecular weight heparin (LMWH) in patients who had exposed during the femoral vein catheterization for apheresis. 74 Patients were randomized 1:1:1 into three groups: subcutaneous injection of LMWH, Fraxiparine (n = 23) (0.4 ml, 3800 IU/day) for 2 days, oral rivaroxaban 10 mg/d (n = 26), and oral rivaroxaban 20 mg/d (n = 25) for consecutive 2 days. The primary endpoint was to compare the venous thromboembolism (VTE) occurrence cases in one month post catheterization. There were 4 cases confirmed VTE occurrence in LMWH group with contrast to 1 case in rivaroxaban 10 mg administration group. None was seen in rivaroxaban 20 mg group (P = 0.02 as the comparison with LMWH). Meantime there was no bleeding events occurrence afterwards. Oral rivaroxaban 20 mg/day was recommendable to be considered which superior to LMWH. Although these limited data and patient volume reached the statistical difference which was able to provide the evidence proofed to compare the potency of those two anticoagulants, it could be regarded as the preliminary data provide the clinical results for cancer patients who were placed in the condition of apheresis and subsequently undergone adoptive T cell immunotherapy.Trial registration ClinicalTrials.gov identifier, NCT03282643. Registered 16 February 2016, http://www.ClinicalTrials.gov/ NCT03282643.

Evaluation of global laboratory methods and establishing on-therapy ranges for monitoring apixaban and rivaroxaban: Experience at a single institution

BACKGROUND

Apixaban and rivaroxaban are approved for the prevention and treatment of deep vein thrombosis (DVT), pulmonary embolism (PE), and embolic stroke in atrial fibrillation (AF) patients. The aim of this study was to find appropriate methods of monitoring the anticoagulant effects of are direct oral anticoagulants (DOACs) and establish on-therapy ranges using conventional tests.

METHODS

A total of 184 samples were collected from 91 patients receiving DOACs. Concentrations of apixaban and rivaroxaban in plasma were accessed by an anti-factor Xa chromogenic assay. PT, APTT, antithrombin, D-dimer, dRVVT screen/confirm, FDP, and fibrinogen levels were measured. On-therapy ranges were calculated by substituting previously reported trough plasma concentrations of DOACs.

RESULTS

Anti-factor Xa chromogenic assay-based DOACs levels were 26.0-279.5 (115.9 ± 56.5) ng/mL for apixaban at 2.5 mg BID, 19.9-565.1 (205.3 ± 162.4) ng/mL for apixaban at 5 mg BID, 2.3-395.3 (205.3 ± 162.4) ng/mL for rivaroxaban at 15 mg OD, 3.6-494.8 (119.6 ± 95.1) ng/mL for rivaroxaban at 20 mg OD, and 9.6-431.4 (140.8 ± 113.6) ng/mL for rivaroxaban at 15 mg BID. PT (%), antithrombin, and dRVVT confirm tests showed good correlation with plasma apixaban levels. Plasma rivaroxaban concentrations were correlated well with PT (sec), PT (%),and dRVVT confirm results. On-therapy ranges established for dRVVT confirm test by linear regression were as follows: 1.32-1.52 for apixaban 2.5 mg BID, 1.12-1.75 for apixaban 5 mg BID, 1.11-1.78 for rivaroxaban 15 mg OD, 1.09-1.64 for rivaroxaban 20 mg OD, and 1.22-1.81 for rivaroxaban 20 mg BID.

CONCLUSIONS

Apixaban concentrations were well correlated with PT (%), antithrombin, and dRVVT confirm test. Rivaroxaban concentrations showed good correlation with PT (sec), PT (%), and dRVVT confirm test.

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.

A Low Rivaroxaban Plasma Level May Indicate Anticoagulation Undertreatment

Few reports have been published on the correlation between plasma concentrations of rivaroxaban and clinical outcome in patients who have experienced venous thromboembolism. This article describes the case of a 44-year-old woman who experienced deep vein thrombosis during anticoagulation therapy with rivaroxaban, with evidence of repeated low plasma levels of the drug. We postulate that the determination of plasma rivaroxaban anti-Xa activity can be useful in the evaluation of anticoagulation therapy in selected cases.

LEARNING POINTS

Some patients with deep vein thrombosis do not respond to rivaroxaban therapy.Accurate determination of rivaroxaban plasma concentrations is important in clinical practice.The clinical value of rivaroxaban plasma concentrations might be limited by intra- and inter-individual variations.

Thrombolysis in an acute ischemic stroke patient with rivaroxaban anticoagulation: A case report

RATIONALE

Whether intravenous recombinant tissue plasminogen activator (r-TPA) therapy can be administered in acute ischemic stroke patients treated with novel oral anticoagulants (NOACs), including rivaroxaban, remains controversial.

PATIENT CONCERNS

A 76-year-old woman with nonvalvular atrial fibrillation, who had been receiving 15 mg rivaroxaban once daily, was brought to the emergency department with right-side hemiparesis and aphasia. The onset of neurological deficits occurred 8 hours after the last dose of rivaroxaban administration.

DIAGNOSIS

The patient was diagnosed with acute ischemic stroke.

INTERVENTIONS

Intravenous infusion of 0.6 mg/kg of r-TPA (total dose: 29 mg) was performed 9 hours and 40 minutes after the last rivaroxaban administration. During r-TPA infusion, improvement in the patient's neurological deficit was observed.

OUTCOMES

The clinical picture evidently improved from with National Institutes of Health Stroke Scale 21 to 16 on completion of r-TPA treatment.

LESSONS

Although current guidelines do not recommend administering thrombolytics in patients using NOACs with a doubtful anticoagulation status and administered within the last 24 or, even more strictly, 48 hours, this and other case studies suggest that r-TPA treatment could be considered in selected acute ischemic stroke patients receiving rivaroxaban or other Xa inhibitors, taking the patient's clinical condition and the prospective clinical benefits of r-TPA into account.

Roles of Coagulation Proteases and PARs (Protease-Activated Receptors) in Mouse Models of Inflammatory Diseases

Activation of the blood coagulation cascade leads to fibrin deposition and platelet activation that are required for hemostasis. However, aberrant activation of coagulation can lead to thrombosis. Thrombi can cause tissue ischemia, and fibrin degradation products and activated platelets can enhance inflammation. In addition, coagulation proteases activate cells by cleavage of PARs (protease-activated receptors), including PAR1 and PAR2. Direct oral anticoagulants have recently been developed to specifically inhibit the coagulation proteases FXa (factor Xa) and thrombin. Administration of these inhibitors to wild-type mice can be used to determine the roles of FXa and thrombin in different inflammatory diseases. These results can be compared with the phenotypes of mice with deficiencies of either Par1 (F2r) or Par2 (F2rl1). However, inhibition of coagulation proteases will have effects beyond reducing PAR signaling, and a deficiency of PARs will abolish signaling from all proteases that activate these receptors. We will summarize studies that examine the roles of coagulation proteases, particularly FXa and thrombin, and PARs in different mouse models of inflammatory disease. Targeting FXa and thrombin or PARs may reduce inflammatory diseases in humans.

Severe Acquired Coagulopathy During Fulminant Staphylococcus aureus Sepsis Most Likely Caused by S. aureus Exotoxins (SSLs)

Haemostatic abnormalities frequently occur during sepsis and are most often attributed to disseminated intravascular coagulation (DIC). We report the case of a patient with severe coagulopathy acquired during fulminant S. aureus sepsis. DIC was not present. This coagulopathy was most likely caused by S. aureus exotoxins forming inhibitory complexes with coagulation factor Xa.

The prothrombotic state in atrial fibrillation: pathophysiological and management implications

Atrial fibrillation (AF) is the commonest sustained cardiac arrhythmia and is associated with significant morbidity and mortality. There is plenty of evidence available to support the presence of a prothrombotic or hypercoagulable state in AF, but the contributory factors are multifactorial and cannot simply be explained by blood stasis. Abnormal changes in atrial wall (anatomical and structural, as ‘vessel wall abnormalities’), the presence of spontaneous echo contrast to signify abnormal changes in flow and stasis (‘flow abnormalities’), and abnormal changes in coagulation, platelet, and other pathophysiologic pathways (‘abnormalities of blood constituents’) are well documented in AF. The presence of these components therefore fulfils Virchow’s triad for thrombogenesis. In this review, we present an overview of the established and professed pathophysiological mechanisms for thrombogenesis in AF and its management implications.

Peak plasma concentration of direct oral anticoagulants in obese patients weighing over 120 kilograms: A retrospective study

BACKGROUND

Due to a paucity of data on the efficacy and safety of direct oral anticoagulants (DOACs) in patients with a body mass index >40 kg/m2 or a weight >120 kg, the use of DOACs in this group is not recommended.

OBJECTIVES

To determine the proportion of obese patients with body weight >120 kg with a peak plasma concentration of DOACs lower than the expected median trough level derived from population pharmacokinetic studies for each DOAC.

METHODS

Patients with body weight >120 kg taking DOACs for any indication underwent a peak drug concentration measurement at steady state.

RESULTS

38 patients were included in the analysis. The mean age was 64 ± 11 years, and 30 (79%) were males. The median body weight was 132.5 kg (interquartile range [IQR] 127-146.5). The median peak concentrations (IQR) were 148 ng/mL (138-240), 138 ng/mL (123-156.5), 215 ng/mL (181-249) for apixaban, dabigatran, and rivaroxaban, respectively. Two patients (5%, 95% confidence interval [CI]: 0.5%-18%) had a peak plasma concentration lower than the median trough and eight (21%, 95% CI: 11%-37%) had a peak plasma concentration below the fifth percentile (10th percentile for dabigatran) peak concentration.

CONCLUSIONS

Most patients in our study had peak plasma concentration higher than the median trough level for each of the three DOACs. However, 21% had a peak plasma concentration that was below the usual on-therapy range of peak concentration for the corresponding DOAC.

Anticoagulation at the extremes of body weight: choices and dosing

INTRODUCTION

The landscape of therapeutic anticoagulation has changed dramatically over the past decade, with availability of direct oral anticoagulants (DOACs), which inhibit factor Xa or thrombin. However, the optimal anticoagulant agent and dosing strategy for patients at both extremes of body weight has not been established for any anticoagulant, including DOACs, vitamin K antagonists (VKA), and the various heparin options. Areas covered: This paper reviews available evidence to assist clinicians in prescribing of anticoagulation therapy at the extremes of body weight. Expert commentary: There are limited data to guide prescribing of all available anticoagulants at the extremes of weight and further research regarding efficacy and safety outcomes in these groups is required. Laboratory monitoring to guide dosing of traditional anticoagulants provides reassurance of 'predictable' efficacy. In contrast agents that are not routinely monitored by laboratory testing provide greater challenges. For example, underweight patients are at risk of receiving higher drug exposures of DOACs, whereas the use of fixed dose DOACs in obese patients may be associated with lower drug exposures.

Comparison of rivaroxaban concentrations between Asians and Caucasians and their correlation with PT/INR

The objectives of this study are to compare steady-state trough (Cmin,ss) and peak (Cmax,ss) concentrations of rivaroxaban between Asians and Caucasians and to evaluate the relationship between rivaroxaban concentrations and prothrombin time/international normalized ratio (PT/INR). Recruited patients were advised on the time to take rivaroxaban. Cmin,ss and PT/INR were taken when patients arrived. Cmax,ss and PT/INR were drawn between 2 and 4 h later after the patient took rivaroxaban with food. Thirty patients were included in the analyses: 57% (n = 17) males and 43% (n = 13) females, 77% (n = 23) on 20 mg and 23% (n = 7) on 15 mg. Median PT_trough and PT_peak are moderately correlated with Cmin,ss (r² = 0.43) and Cmax,ss (r² = 0.49), respectively. Patients on 15 mg have lower Cmin,ss and Cmax,ss versus Caucasians [12 ng/ml vs. 57 ng/ml (Cmin,ss); 87 ng/ml vs. 229 ng/ml (Cmax,ss), p < 0.01 for both]. Patients on 20 mg also have lower Cmin,ss and Cmax,ss versus Caucasians [14 ng/ml vs. 44 ng/ml (Cmin,ss); 101 ng/ml vs. 249 ng/ml (Cmax,ss), p < 0.01 for both]. Subgroup analysis shows patients with BMI ≥ 30 have lower Cmax,ss than patients with BMI < 30 [80.47 ng/ml vs. 124 (p = 0.014)]. Cmin,ss and Cmax,ss were lower in Singaporeans than Caucasians. This may have an impact on the effectiveness of rivaroxaban in Singaporeans. Patients with higher BMI may not benefit similarly as patients with lower BMI. Lastly, the Dade Innovin reagent's measure of PT/INR is not sensitive towards changes in rivaroxaban concentrations.

Coagulation Testing in Intracerebral Hemorrhage Related to Non-vitamin K Antagonist Oral Anticoagulants

BACKGROUND

Intracerebral hemorrhage (ICH) is a life-threatening complication of non-vitamin K antagonist oral anticoagulants (NOAC). Little is known about the effect of intensity of anticoagulation on NOAC-ICH. We describe the current use of coagulation testing in the emergency setting and explore associations with baseline size and expansion of hematoma as determined in a previous study.

METHODS

Data from the prospective multicenter RASUNOA registry were analyzed. Patients with NOAC-ICH were enrolled between February 2012 and December 2014. Frequency of local test performance of specific (anti-factor Xa tests, diluted thrombin time) and non-specific tests (international normalized ratio (INR), activated partial thromboplastin time (aPTT), thrombin time) was analyzed. The association of anticoagulation intensity at admission with hematoma volume and hematoma expansion was explored.

RESULTS

In 61 NOAC-ICH patients enrolled at 21 centers, drug-specific coagulation testing was performed in 16 cases (26%), and only 29% of centers appeared to use drug-specific tests in NOAC-ICH at all. In some cases, INR and aPTT values were normal despite drug concentrations in the peak range. In patients with available drug-specific concentrations, 50% had drug levels in the peak range at admission. Higher intensity of anticoagulation was not associated with higher hematoma volume at admission or with subsequent hematoma expansion.

CONCLUSION

Drug-specific tests are only infrequently used in NOAC-ICH. Normal results in non-specific coagulation do not reliably rule out peak range concentrations. Anticoagulation intensity at admission does not predict baseline hematoma volume or subsequent hematoma expansion.

The prothrombin time does not predict the risk of recurrent venous thromboembolism or major bleeding in rivaroxaban-treated patients

INTRODUCTION

For treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE), rivaroxaban is given in fixed doses without routine coagulation monitoring.

PATIENTS AND METHODS

To determine whether monitoring would enhance its benefit-risk profile, we examined whether peak and trough prothrombin time (PT) values measured in 3797 rivaroxaban-treated patients included in the EINSTEIN DVT and PE studies correlated with subsequent recurrent VTE and major bleeding. In addition, we examined the stability of PT values over time and the impact of clinical variables on PT values.

RESULTS

The mean peak PT values at months 3 and 6 or 12 were 21.9 ± 5 and 21.7 ± 6.0 s, respectively, while the mean trough PT values at months 2 and 6 were 15.1 ± 5.1 and 15.3 ± 2.9 s, respectively. Although peak and through PT values were higher in females, and with older age, frailty, active cancer, low body weight, impaired renal function and use of moderate to strong inhibitors of CYP3A4 and/or P-glycoprotein, and were lower in patients taking strong CYP 3A4 inducers, the differences were small and results were overlapping. Neither peak nor trough PT values correlated with recurrent VTE or major bleeding.

CONCLUSIONS

PT monitoring is unlikely to improve the benefit-risk profile of rivaroxaban in patients with DVT or PE. The study was registered at www.clinicaltrials.gov as #NCT00440193 (EINSTEIN-DVT) and #NCT00439777 (EINSTEIN-PE).