Safety, pharmacokinetics and pharmacodynamics of single/multiple doses of the oral, direct Factor Xa inhibitor rivaroxaban in healthy Chinese subjects

Bioequivalence Study of Capsules versus Film Tablets Containing Rivaroxaban in Healthy Caucasian Subjects under Fasting and Fed Conditions

The bioequivalence (BE) of orally administered capsules versus film tablets containing 20  and 10 mg of rivaroxaban was assessed in 2 single-dose, open-label, randomized 2-way crossover trials with a washout period of at least 1 week. The study for the 10 mg strength was conducted under fasting conditions (n = 68) and the study for the 20 mg strength under fed conditions (n = 52). Blood samples were collected over a 36-hour period and concentrations were assayed using a liquid chromatography tandem mass spectrometry method. Pharmacokinetic (PK) evaluation was performed with the program Phoenix WinNonlin, for non-compartmental assessment of data. After administration of 10 mg rivaroxaban under fasting conditions, mean Area Under the time - concentration Curve until the last blood sampling point (AUCt ), Area Under the time - concentration Curve until infinity (AUC∞ ), and maximum plasma concentration (Cmax ) were comparable (972 ng/mL*h, 1048 ng/mL*h, and 111 ng/mL, respectively, for the test and 1013 ng/mL*h, 1070 ng/mL*h and 130 ng/mL, respectively, for the reference formulation). Mean AUCt , AUC∞ , and Cmax were also comparable under fed conditions after administration of 20 mg rivaroxaban (2145 ng/mL*h, 2198 ng/mL*h and 275 ng/mL, respectively, for the test and 1856 ng/mL*h, 1916 ng/mL*h and 240 ng/mL, respectively, for the reference formulation). The 90% confidence intervals for all PK parameters were within the acceptance range of 80%-125%, suggesting BE between the generic product and the innovator product in healthy Caucasian male subjects. A clinically relevant difference in the tolerability and safety of the treatments was not detected. Study results indicated that the capsule formulations were bioequivalent with the film tablet formulations.

Effect of a High-Fat Diet on the Pharmacokinetics and Safety of Rivaroxaban in Healthy Chinese Subjects

The effects of food on the pharmacokinetics (PKs) and safety of 10-mg rivaroxaban tablets in healthy Chinese subjects were investigated from 1 bioequivalence trial. The bioequivalence trial was designed as randomized, open-label, 2-sequence, 4-period crossover under both fasted and fed conditions. A total of 56 healthy subjects were enrolled, 62.5% were male. These subjects received a single oral 10-mg dose of rivaroxaban with a 7-day washout between 4 periods. Serial PK samples were collected and plasma concentrations were analyzed using validated high-performance liquid chromatography-mass spectrometry. Pharmacokinetic parameters were calculated by noncompartmental methods. The BE module of WinNonLin was used for statistical analysis of the maximum concentration (Cmax ), the area under the concentration-time curve from zero to the final measurable concentration (AUC0-t ), and the area under the concentration-time curve from time zero to infinity (AUC0-∞ ) of rivaroxaban in plasma. Compared with the fasted state, the Cmax , AUC0-t , and AUC0-∞ of rivaroxaban significantly increased by 47%, 28%, and 26%, respectively, with oral administration of rivaroxaban 10 mg in the fed state. The incidence of adverse events (AEs) was similar between the fasted and fed states, and no serious AEs were observed. Food significantly increased the exposure to rivaroxaban 10 mg in Chinese subjects.

Comparisons of effectiveness and safety between on-label dosing, off-label underdosing, and off-label overdosing in Asian and non-Asian atrial fibrillation patients treated with rivaroxaban: a systematic review and meta-analysis of observational studies

AIMS

Limited real-world data show that rivaroxaban following dosage criteria from either ROCKET AF [20 mg/day or 15 mg/day if creatinine clearance (CrCl) < 50 mL/min] or J-ROCKET AF (15 mg/day or 10 mg/day if CrCl < 50 mL/min) is associated with comparable risks of thromboembolism and bleeding with each other in patients with non-valvular atrial fibrillation (NVAF). We are aimed to study whether these observations differ between Asian and non-Asian subjects.

METHODS AND RESULTS

A systematic review and meta-analysis with random effects was conducted to estimate the aggregate hazard ratio (HR) and 95% confidence interval (CI) using PubMed and MEDLINE databases from 8 September 2011 to 31 December 2022 searched for adjusted observational studies that reported relevant clinical outcomes of NVAF patients receiving rivaroxaban 10 mg/day if CrCl > 50 mL/min, on-label dose rivaroxaban eligible for ROCKET AF or J-ROCKET AF, and rivaroxaban 20 mg/day if CrCl < 50 mL/min. Effectiveness and safety endpoints were compared between ROCKET AF and J-ROCKET AF dosing regimen in Asian and non-Asian subjects, separately. Also, risks of events of rivaroxaban 10 mg/day despite of CrCl > 50 mL/min and rivaroxaban 20 mg/day despite of CrCl < 50 mL/min were compared to that of 'ROCKET AF/J-ROCKET AF dosing'. Sensitivity analyses were performed by sequential elimination of each study from the pool. The meta-regression analysis was performed to explore the influence of potential factors on the effectiveness and safety outcomes. Eighteen studies involving 67 571 Asian and 54 882 non-Asian patients were included. Rivaroxaban following J-ROCKET AF criteria was associated with comparable risks of thromboembolism in the Asian subgroup, whereas rivaroxaban following J-ROCKET AF criteria was associated with higher risks of all-cause mortality (HR:1.30; 95% CI:1.05-1.60) compared with that of ROCKET AF criteria in the non-Asian population. There were no differences in risks of major bleeding between rivaroxaban following J-ROCKET AF vs. ROCKET AF criteria either in the Asian or non-Asian population. The use of rivaroxaban 10 mg despite of CrCl > 50 mL/min was associated with a higher risk of thromboembolism (HR:1.64; 95% CI:1.28-2.11) but lower risk of major bleeding (HR:0.72; 95% CI:0.57-0.90) compared with eligible dosage criteria. The use of rivaroxaban 20 mg despite of CrCl < 50 mL/min was associated with worse clinical outcomes in the risks of thromboembolism (HR:1.32; 95% CI:1.09-1.59), mortality (HR:1.33; 95% CI:1.10-1.59), and major bleeding (HR:1.26; 95% CI:1.03-1.53) compared with eligible dosage criteria. The pooled results were generally in line with the primary effectiveness and safety outcomes by removing a single study at one time. Meta-regression analyses failed to detect the bias in most potential patient characteristics associated with the clinical outcomes.

CONCLUSION

Rivaroxaban dosing regimen following J-ROCKET criteria may serve as an alternative to ROCKET AF criteria for the Asian population with NVAF, whereas the dosing regimen following ROCKET AF criteria was more favourable for the non-Asian population. The use of rivaroxaban 10 mg despite of CrCl > 50 mL/min was associated with a higher risk of thromboembolism but a lower risk of major bleeding, while use of rivaroxaban 20 mg despite of CrCl < 50 mL/min was associated with worse outcome in most clinical events.

Application of the Population Pharmacokinetics Model-Based Approach to the Prediction of Drug-Drug Interaction between Rivaroxaban and Carbamazepine in Humans

Rivaroxaban (RIV) is one of the direct oral anticoagulants used to prevent and treat venous and arterial thromboembolic events. Considering the therapeutic indications, RIV is likely to be concomitantly administered with various other drugs. Among these is carbamazepine (CBZ), one of the recommended first-line options to control seizures and epilepsy. RIV is a strong substrate of cytochrome P450 (CYP) enzymes and Pgp/BCRP efflux transporters. Meanwhile, CBZ is well known as a strong inducer of these enzymes and transporters. Therefore, drug-drug interaction (DDI) between CBZ and RIV is expected. This study aimed to predict the DDI profile of CBZ and RIV in humans by using a population pharmacokinetics (PK) model-based approach. We previously investigated the population PK parameters of RIV administered alone or with CBZ in rats. In this study, those parameters were extrapolated from rats to humans by using simple allometry and liver blood flow scaling, and then applied to back-simulate the PK profiles of RIV in humans (20 mg RIV per day) used alone or with CBZ (900 mg CBZ per day). Results showed that CBZ significantly reduced RIV exposure. The AUC_inf and C_max of RIV decreased by 52.3% and 41.0%, respectively, following the first RIV dose, and by 68.5% and 49.8% at the steady state. Therefore, the co-administration of CBZ and RIV warrants caution. Further studies investigating the extent of DDIs between these drugs should be conducted in humans to fully understand their safety and effects.

Generic Methods for Simultaneous Analysis of Four Direct Oral Anticoagulants in Human Plasma and Urine by Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry

The new direct oral anticoagulants (DOACs) are increasingly used to treat and prevent thromboembolic disorders, and monitoring concentrations may be valuable in some special scenarios to prevent clinical adverse events. This study aimed to develop generic methods for the rapid and simultaneous analysis of four DOACs in human plasma and urine. Protein precipitation and one-step dilution were used to prepare the plasma and urine; the extracts were injected to ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for analysis. Chromatographic separation was performed on an Acquity™ UPLC BEH C₁₈ column (2.1 × 50 mm, 1.7 μm) with gradient elution of 7 min. A triple quadrupole tandem mass spectrometer with an electrospray ionization source was employed to analyze DOACs in a positive ion mode. The methods showed great linearity in the plasma (1~500 ng/mL) and urine (10~10,000 ng/mL) for all analytes (R² ≥ 0.99). The intra- and inter-day precision and accuracy were within acceptance criteria. The matrix effect and extraction recovery were 86.5~97.5% and 93.5~104.7% in the plasma, while 97.0~101.9% and 85.1~99.5% in the urine. The stability of samples during the routine preparation and storage were within the acceptance criteria of less than ±15%. The methods developed were accurate, reliable, and simple for the rapid and simultaneous measurement of four DOACs in human plasma and urine, and successfully applied to patients and subjects with DOACs therapy for anticoagulant activity assessment.

Is a Lower Dose of Rivaroxaban Required for Asians? A Systematic Review of a Population Pharmacokinetics and Pharmacodynamics Analysis of Rivaroxaban

Rivaroxaban has been widely used to prevent and treat various thromboembolic diseases for more than a decade. However, whether a lower dose of rivaroxaban is required for Asians is still debatable. This review aimed to explore the potential ethnic difference in pharmacokinetic/pharmacodynamic (PK/PD) characteristics between Asians and Caucasians. A systematic search was conducted and twenty-four studies were identified, of which 10 were conducted on Asian adults, 11 on predominantly Caucasian adults, and 3 on Caucasian pediatrics. The apparent clearance (CL/F) of rivaroxaban in Caucasian adults with non-valvular atrial fibrillation (6.45-7.64 L/h) was about 31-43% higher than that in Asians (4.46-5.98 L/h) taking 10~20 mg rivaroxaban every 24 h. Moreover, there was no obvious difference in CL/F among Japanese, Chinese, Thai, and Irani people. Regarding PK/PD relationship, prothrombin time was linked to rivaroxaban concentration in a linear or near-linear manner, and Factor Xa activity was linked with the E_max model. The exposure-response relationship was comparable between Asians and Caucasians. Renal function has a significant influence on CL/F, and no covariate was recognized for exposure-response relationship. In conclusion, a lower dose of rivaroxaban might be required for Asians, and further studies are warranted to verify this ethnic difference to facilitate optimal dosing regimens.

Application of physiologically-based pharmacokinetic model approach to predict pharmacokinetics and drug-drug interaction of rivaroxaban: A case study of rivaroxaban and carbamazepine

Rivaroxaban (RIV; Xarelto; Janssen Pharmaceuticals, Beerse, Belgium) is one of the direct oral anticoagulants. The drug is a strong substrate of cytochrome P450 (CYP) enzymes and efflux transporters. This study aimed to develop a physiologically-based pharmacokinetic (PBPK) model for RIV. It contained three hepatic metabolizing enzyme reactions (CYP3A4, CYP2J2, and CYP-independent) and two active transporter-mediated transfers (P-gp and BCRP transporters). To illustrate the performance of the developed RIV PBPK model on the prediction of drug-drug interactions (DDIs), carbamazepine (CBZ) was selected as a case study due to the high DDI potential. Our study results showed that CBZ significantly reduces the exposure of RIV. The area under the concentration-time curve from zero to infinity (AUC_inf ) of RIV was reduced by 35.2% (from 2221.3 to 1438.7 ng*h/ml) and by 25.5% (from 2467.3 to 1838.4 ng*h/ml) after the first dose and at the steady-state, respectively, whereas the maximum plasma concentration (C_max ) of RIV was reduced by 37.7% (from 266.3 to 166.1 ng/ml) and 36.4% (from 282.3 to 179.5 ng/ml), respectively. The developed PBPK model of RIV could be paired with PBPK models of other interested perpetrators to predict DDI profiles. Further studies investigating the extent of DDI between CBZ and RIV should be conducted in humans to gain a full understanding of their safety and effects.

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.

Rationale and design of a prospective study evaluating population pharmacokinetics and pharmacodynamics of rivaroxaban in Chinese patients with non-valvular atrial fibrillation

INTRODUCTION

Rivaroxaban is one of the most commonly used non-vitamin K antagonists for stroke prevention in patients with non-valvular atrial fibrillation (NVAF). Different individual exposures exist for Asian and non-Asian populations, and dose selection is different for Japanese and non-Japanese subjects. Few studies have investigated the pharmacokinetics (PK) and pharmacodynamics (PD) of rivaroxaban in Chinese patients and provided a solid reference for dose selection and individualised therapy.

METHODS AND ANALYSIS

This is a single-centre prospective study. Rivaroxaban-treated Chinese NVAF patients will be recruited according to predetermined inclusion criteria. Blood samples will be collected from both outpatients and inpatients with different sampling strategies at steady state. Rivaroxaban plasma concentration, factor Xa activity, prothrombin time and single-nucleotide polymorphisms of candidate genes will be evaluated. Follow-up will be conducted following 3 and 6 months after enrolment to collect information about the safety and efficacy outcomes. A nonlinear mixed-effects modelling strategy will be used to develop a population PK-PD model of rivaroxaban.

ETHICS AND DISSEMINATION

The study has been approved by the Ethics Committee of Huashan Hospital, Fudan University (KY2020-016). The study findings will be submitted to peer-reviewed journals and shared with public health authorities.

TRIAL REGISTRATION NUMBER

ChiCTR2100046685.

A Single-blind, Randomized, Single-dose, Two-sequence, Two-period, Crossover Study to Assess the Bioequivalence between Two Oral Tablet Formulations of Rivaroxaban 20 mg in Healthy Mexican Volunteers

The objective of this study was to demonstrate the bioequivalence of 2 oral tablet formulations of rivaroxaban 20 mg in healthy Mexican volunteers under fed conditions. This phase I, single‐blind, single‐dose, randomized, two‐sequence, two‐period crossover study included 32 volunteers. Subjects were randomly assigned to one of two sequences: test formulation (single 20 mg dose) in the first period followed by the reference formulation (single 20 mg dose) in the second, or vice versa. Blood samples were collected predose and at predefined timepoints across a 48‐hour period after drug intake. Rivaroxaban plasma concentrations were measured using a validated high‐performance liquid chromatography‐tandem mass spectrometry method. Pharmacokinetic parameters included maximum plasma concentration (C_max), area under the plasma concentration‐time curve from time zero to last measurable concentration and to infinity (AUC_0‐t, AUC_0‐∞), time to reach C_max, and half‐life. Safety was evaluated through adverse‐event monitoring using subject interviews and recording of vital signs. The 90% confidence intervals for the test/reference geometric mean ratios of C_max (100.4%–112.7%), AUC_0‐t (96.5%–111.6%), and AUC_0‐∞ (95.5%–109.5%) were within the bioequivalence acceptance range (80‐125%). Two adverse events (headaches) were recorded. Both formulations of rivaroxaban 20 mg tablets were bioequivalent and well tolerated in a healthy population of Mexican volunteers under fed conditions.

Rivaroxaban population pharmacokinetic and pharmacodynamic modeling in Iranian patients

WHAT IS KNOWN AND OBJECTIVE

Although predictable pharmacokinetic and pharmacodynamic of rivaroxaban allow fixed dosing regimens without routine coagulation monitoring, there is still the necessity to monitor and predict the effects of rivaroxaban in specific conditions and different populations. The current study was designed and conducted to analyze the rivaroxaban population pharmacokinetics in Iranian patients and establish a pharmacokinetic/pharmacodynamic model to predict the relationship between rivaroxaban concentration and its anticoagulant activity.

METHODS

A sequential nonlinear mixed effect pharmacokinetic/pharmacodynamic modeling method was used to establish the relation between rivaroxaban concentration and anti-factor Xa activity, prothrombin time, and activated partial thromboplastin time (aPTT) as pharmacodynamic biomarkers in a population of sixty-nine Iranian patients under treatment with oral rivaroxaban. Rivaroxaban plasma concentration was quantified by a validated high-performance liquid chromatography-tandem mass spectrometry.

RESULTS AND DISCUSSION

The typical population values (inter-individual variability%) of the oral volume of distribution and clearance for a one-compartment model were 61.2 L (21%) and 3.68 L·h^-1 (61%), respectively. Creatinine clearance and Child-Turcotte-Pugh score were found to affect the clearance. A direct link linear structural model best fitted the data for both prothrombin time and aPTT. The baseline estimates of aPTT and prothrombin time in the population were 35.0 (15%) and 12.6 (2%) seconds, respectively. The slope of the relationship between apTT, prothrombin time, and rivaroxaban concentration was 0.033 (28%) and 0.018 (54%) s·ml·ng^-1 , respectively. The selected model for anti-factor Xa activity consisted of a direct link inhibitory E_max model with Hill coefficient. The maximum level of inhibition (E_max ) was 4 IU·ml^-1 . The concentration of rivaroxaban producing 50% of the maximum inhibitory effect (EC₅₀ ) was 180 (24%) ng·ml^-1 , and Hill coefficient (γ) was 1.44 (108%). No covariates showed a statistically significant effect on PT and activated partial thromboplastin time prolonging properties and anti-factor Xa activity.

WHAT IS NEW AND CONCLUSION

Our results confirmed that pharmacokinetic/pharmacodynamic models similar to those of the other studies describe the relationship between the rivaroxaban concentration and its anticoagulant effect in Iranian patients. However, considerable differences were observed in the parameters of the pharmacodynamics-pharmacokinetic models with the results of other reports that can explain the unpredictable effects of rivaroxaban in some patients.

A Combined Pharmacometrics Analysis of Biomarker Distribution Under Treatment With Standard- or Low-Dose Rivaroxaban in Real-World Chinese Patients With Nonvalvular Atrial Fibrillation

Background: The rivaroxaban dose regimen for patients with nonvalvular atrial fibrillation (NVAF) is complex in Asia. Given the high interindividual variability and the risk of bleeding caused by rivaroxaban in Asians, the influencing factors and the relationship between outlier biomarkers and bleeding events need exploration.

Methods: The integrated pharmacokinetics (PK)/pharmacodynamics (PD) models were characterized based on rich PK/PD data from 304 healthy volunteers and sparse PD [anti-factor Xa activity (anti-Xa) and prothrombin (PT)] data from 223 patients with NVAF. The correlations between PD biomarkers and clinically relevant bleedings in 1 year were explored. The final integrated PK/PD model was used to evaluate the influence of dosage and individual covariates on PD parameters.

Results: A two-compartment, linear model with sequential zero-order and first-order absorption was adopted. The dose-specific relative bioavailability (F₁), diet status, creatinine clearance, and body mass index (BMI) improved the model fit. The apparent systemic clearance was 7.39 L/h, and the central and peripheral volumes were 10.9 and 50.9 L, respectively. The linear direct-effects model with shape factor plus the additive (and/or proportional) error model described the correlation between anti-Xa/PT and plasma concentration. Bodyweight, total cholesterol (TCHO), and diet status were selected as the covariates of the anti-Xa/PT model. Anti-Xa was more sensitive to the increase in rivaroxaban exposure compared with PT. An elevated bleeding tendency was seen with higher peak anti-Xa and PT. For a typical Chinese patient, the peak anti-Xa value (median (5%–95% PI)) of 20 and 15 mg were 309 ng/ml (139–597 ng/ml) and 296 ng/ml (138–604 ng/ml), both median values were within the expected range. For patients with CrCL 30–49 ml/min, the median peak anti-Xa with recommended 10 mg other than 15 mg were within the expected range.

Conclusion: Fixed doses of rivaroxaban could be prescribed for patients with NVAF without adjustment for bodyweight, BMI, and TCHO. Randomized studies should be performed to evaluate the efficacy and safety of low-dose rivaroxaban in Chinese patients with NVAF.

Inter- and intra-individual concentrations of direct oral anticoagulants: The KIDOAC study

BACKGROUND

Direct oral anticoagulants (DOACs) do not require concentration monitoring. However, whether DOAC concentrations are stable and their variation between and within patients is not well studied.

METHODS

Patients on vitamin K antagonists (VKA) who switched to rivaroxaban, apixaban, or dabigatran were included between 2018 and 2020. Blood was drawn at DOAC trough and peak concentrations at week 0, 2, and 8. Plasma drug concentrations were determined by anti-factor Xa concentrations (rivaroxaban, apixaban) or diluted thrombin time (dabigatran). Inter- and intra-individual variability was assessed by calculating the coefficient of variation (CV). Linear regression models were employed to evaluate associations between DOAC trough concentrations and previous VKA dosage, creatinine clearance, and body mass index (BMI).

RESULTS

One hundred fifty-two patients were included, of whom 96 (63%) were male and with a mean age of 73.9 ± 8.4 years. For the inter-individual variability, the CV ranged between 48% and 81% for trough values and between 25% and 69% for peak values among patients using the recommended DOAC dose. Intra-individual variability was substantially lower, as here the CV ranged between 18% and 33% for trough values and between 15% and 29% for peak values among patients using the recommended DOAC dose. Previous VKA dosage and creatinine clearance were inversely associated with DOAC trough concentrations. No association was found between BMI and DOAC trough concentrations.

CONCLUSION

Inter-individual variability of DOAC concentrations was higher than intra-individual variability. Lower previous VKA dosage and creatinine clearance were associated with higher DOAC trough concentrations. These findings support further study into an optimal target range, in which the risks of both bleeding and thrombosis are minimal.

Population pharmacokinetic analysis of rivaroxaban in children and comparison to prospective physiologically-based pharmacokinetic predictions

Rivaroxaban has been investigated in the EINSTEIN‐Jr program for the treatment of acute venous thromboembolism (VTE) in children aged 0 to 18 years and in the UNIVERSE program for thromboprophylaxis in children aged 2 to 8 years with congenital heart disease after Fontan‐procedure. Physiologically‐based pharmacokinetic (PBPK) and population pharmacokinetic (PopPK) modeling were used throughout the pediatric development of rivaroxaban according to the learn‐and‐confirm paradigm. The development strategy was to match pediatric drug exposures to adult exposure proven to be safe and efficacious. In this analysis, a refined pediatric PopPK model for rivaroxaban based on integrated EINSTEIN‐Jr data and interim PK data from part A of the UNIVERSE phase III study was developed and the influence of potential covariates and intrinsic factors on rivaroxaban exposure was assessed. The model adequately described the observed pediatric PK data. PK parameters and exposure metrics estimated by the PopPK model were compared to the predictions from a previously published pediatric PBPK model for rivaroxaban. Ninety‐one percent of the individual post hoc clearance estimates were found within the 5th to 95th percentile of the PBPK model predictions. In patients below 2 years of age, however, clearance was underpredicted by the PBPK model. The iterative and integrative use of PBPK and PopPK modeling and simulation played a major role in the establishment of the bodyweight‐adjusted rivaroxaban dosing regimen that was ultimately confirmed to be a safe and efficacious dosing regimen for children aged 0 to 18 years with acute VTE in the EINSTEIN‐Jr phase III study.

Novel assay based on diluted prothrombin time reflects anticoagulant effects of direct oral factor Xa inhibitors: Results of multicenter study in Japan

BACKGROUND

Direct oral anticoagulants targeting factor Xa (DXaIs) are administered as prophylaxis for various venothrombotic diseases without routine monitoring required. However, assessment of their anticoagulant effects is necessary to prevent severe events, including major bleeding and/or refractory thrombosis.

OBJECTIVES

We examined the correlation of ratio of inhibited thrombin generation (RITG), determined using a novel assay based on dilute prothrombin time (dPT), with coagulant markers and laboratory test results to show drug effects. In addition, RITG usefulness as a confirmation test for DXaI therapy was investigated.

METHODS

Citrated plasma samples were obtained from patients treated with rivaroxaban (n = 882), apixaban (n = 1214), or edoxaban (n = 820) at 4 different institutions in Japan. Laboratory tests, including prothrombin time (PT), activated partial thromboplastin time (APTT), D-dimer, and plasma concentrations of DXaIs, were conducted, with drug concentrations divided into peak and trough groups, within and after 5 h of administration.

RESULTS

In each DXaI group, RITG was positively correlated with PT, APTT, and drug concentration, and negatively with D-dimer. RITG fluctuation during the peak and trough periods reflected the anticoagulant activity characteristic of each DXaI, which was different from blood concentration fluctuations. RITG showed a significant decrease in cases with thrombosis, while that was increased in those with hemorrhage.

CONCLUSION

We developed RITG, a novel measurement method based on dPT. RITG represents residual coagulation ability in plasma samples, and is useful for assessment of bleeding and thrombotic tendencies in DXaI patients. RITG can be utilized to confirm the effectiveness of oral anticoagulation therapy with DXaI agents.

The Timing of Symptomatic Pulmonary Embolism in Patients With Nonwarfarin Anticoagulants Following Elective Primary Total Joint Arthroplasty

BACKGROUND

The purpose of this study is to investigate the incidence and timing of postoperative, symptomatic pulmonary embolism (PE) in patients receiving nonwarfarin treatment following primary total joint arthroplasty (TJA), to clarify the appropriate duration of postoperative VTE prophylaxis.

METHODS

We retrospectively reviewed the medical records of 11,148 patients who underwent primary TJA, including total knee arthroplasty and total hip arthroplasty at our institution between January 2012 and March 2019. The median postoperative day of diagnosis of symptomatic PE and the interquartile range for day of diagnosis were determined. Multivariate Cox proportional hazards modeling was used to test the difference of timing for PE based on demographics and comorbidities.

RESULTS

The overall 90-day rate of symptomatic PE was 0.71%. The median day of diagnosis for symptomatic PE was 3 days postoperatively (interquartile range, 2-7 days). Factors showed statistical significance on multivariate analysis in association with earlier timing of PE occurrence in patients with atrial fibrillation, diabetes mellitus, coronary heart disease, and history of stroke.

CONCLUSION

The vast majority of symptomatic PE occurs in the early postoperative period after TJA, and atrial fibrillation, diabetes mellitus, coronary heart disease, and history of stroke were independent factors affecting the timing of symptomatic PE.

Real-World Rivaroxaban and Apixaban Levels in Asian Patients With Atrial Fibrillation

This study aims to measure the plasma levels of rivaroxaban and apixaban among Asian patients with atrial fibrillation and compare the results with expected drug levels from clinical studies. A total of 73 patients taking rivaroxaban and 105 patients taking apixaban were enrolled. Peak and trough levels were measured using ultra-high performance liquid chromatography with tandem mass spectrometry. The percentage of those with drug levels within the expected range reported in clinical studies was significantly higher in the apixaban group than in the rivaroxaban group, both for trough (84.8% vs. 64.4%; P = 0.002) and peak levels (76.9% vs. 33.8%; P < 0.001). After adjusting for age, sex, kidney function, appropriate dose, and adherence, patients taking rivaroxaban were still less likely to have peak and trough levels within the expected drug levels. Our real-world data suggests that Asian patients taking rivaroxaban are more likely to have out-of-expected drug levels than those taking apixaban.

Pharmacokinetic Properties of Rivaroxaban in Healthy Human Subjects

Direct oral anticoagulants (DOACs) have predictable pharmacokinetics and pharmacodynamics, limited potential for drug to drug interactions, and can be given at fixed doses without the need for routine coagulation monitoring, which makes them a very attractive alternative to vitamin K antagonists. DOACs act by specifically targeting a single coagulation factor, such as Factor Xa or thrombin. Rivaroxaban is a direct Factor Xa inhibitor and has been approved for use in several thromboembolic disorders, such as the prevention of stroke and systemic embolism in adults with non-valvular atrial fibrillation and the prevention of recurrent deep vein thrombosis and pulmonary embolism in adult patients. This review aimed to provide an overview of the mechanism of action of rivaroxaban and outline its pharmacokinetic properties (absorption, distribution, metabolism, and excretion) in healthy adult subjects.

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.

An analysis on distribution and inter-relationships of biomarkers under rivaroxaban in Japanese patients with non-valvular atrial fibrillation (CVI ARO 1)

Prothrombin time (PT) has been widely used for measuring anticoagulation intensity under rivaroxaban therapy, but precise information has not been well established yet. Consecutive 96 non-valvular atrial fibrillation (NVAF) under rivaroxaban between Jan/June, 2015 were recruited. Serum concentration (SC) and PT with 5 representative reagents available in Japan (Neoplastin Plus®, Thromborel S®, Thrombocheck PT®, Thrombocheck PT Plus®, and Recombiplastin®) at 2-4 hours after (peak) and before intake of rivaroxaban (trough) were measured at outpatient clinic in the cardiovascular institute (CVI ARO study 1). Nonlinear mixed-effects modelling was used to model the population pharmacokinetics and pharmacodynamics of rivaroxaban. An oral one-compartment model was employed to describe the population pharmacokinetics of rivaroxaban. The pharmacokinetics of rivaroxaban were affected by creatinine clearance, alanine aminotransferase, and use of CYP3A4 or P-gp inhibitors. PTs with 5 reagents were predicted by pharmacodinamic models with SC, hematocrit, serum albumin, and age, with medium predicting ability (highest/lowest R2 = 0.746/0.658 in Recombiplastin/Thromborel S, respectively). This population analysis in NVAF patients under rivaroxaban therapy demonstrated that pharmacokinetics of rivaroxaban was described by an oral one-compartment model with expected covariates, and can be assessed by PT with available reagents in Japan with medium predicting ability.

Application of physiologically based pharmacokinetic modeling to the prediction of drug-drug and drug-disease interactions for rivaroxaban

PURPOSE

Rivaroxaban is a direct oral anticoagulant with a large inter-individual variability. The present study is to develop a physiologically based pharmacokinetic (PBPK) model to predict several scenarios in clinical practice.

METHODS

A whole-body PBPK model for rivaroxaban, which is metabolized by the cytochrome P450 (CYP) 3A4/5, 2J2 pathways and excreted via kidneys, was developed to predict the pharmacokinetics at different doses in healthy subjects and patients with hepatic or renal dysfunction. Hepatic clearance and drug-drug interactions (DDI) were estimated by in vitro in vivo extrapolation (IVIVE) based on parameters obtained from in vitro experiments. To validate the model, observed concentrations were compared with predicted concentrations, and the impact of special scenarios was investigated.

RESULTS

The PBPK model successfully predicted the pharmacokinetics for healthy subjects and patients as well as DDIs. Sensitivity analysis shows that age, renal, and hepatic clearance are important factors affecting rivaroxaban pharmacokinetics. The predicted fold increase of rivaroxaban AUC values when combined administered with the inhibitors such as ketoconazole, ritonavir, and clarithromycin were 2.3, 2.2, and 1.3, respectively. When DDIs and hepatic dysfunction coexist, the fold increase of rivaroxaban exposure would increase significantly compared with one factor alone.

CONCLUSIONS

Our study using PBPK modeling provided a reasonable approach to evaluate exposure levels in special patients under special scenarios. Although further clinical study or real-life experience would certainly merit the current work, the modeling work so far would at least suggest caution of using rivaroxaban in complicated clinical settings.

Phamacokinetics of rivaroxaban in adolescents

Background: The direct factor Xa inhibitor rivaroxaban is approved for venous throm-boembolism (VTE) treatment in adults. However, in all phase-III trials children or adolescents have not been included. For under-aged VTE patients, current standard treatment consists of low molecular weight heparin or Vitamin K antagonists. Rivaroxaban could be an attractive alternative, however, no data on the pharmacokinetics (PK) of rivaroxaban in adolescents are currently available.

Patient, methods: We report PK data for rivaroxaban derived from a girl (age:15 years), who presented three month after acute deep vein thrombosis, already receiving rivaroxaban therapy. In the steady state of rivaroxaban therapy (20 mg once daily), plasma levels at baseline, 3 and 6 hours after intake of rivaroxaban were measured to evaluate the pharmacokinetics and changes of global coagulation tests.

Results: At baseline, a very low trough level of only 9.9 ng/ml rivaroxaban was found. At 3 hours, a peak concentration of 137.76 ng/ml rivaroxaban was observed with a rapid decrease within 6 hours after drug intake, when plasma levels of 34.45 ng/ml were measured. The patients INR and aPTT values reacted correspondingly.

Conclusion: Our data indicate that adolescents may exhibit lower peak and trough levels after rivaroxaban intake compared to adult patients, but seem to have similar PK curves during the elimination phase. While our case is the first published case of a successful VTE treatment in an under-aged , we strongly discourage the routine use of rivaroxaban in non-adult patients, until data from phase II and III trials are available.

Rivaroxaban vs Warfarin Sodium in the Ultra-Early Period After Atrial Fibrillation-Related Mild Ischemic Stroke: A Randomized Clinical Trial

Importance

In atrial fibrillation (AF)-related acute ischemic stroke, the optimal oral anticoagulation strategy remains unclear.

Objective

To test whether rivaroxaban or warfarin sodium is safer and more effective for preventing early recurrent stroke in patients with AF-related acute ischemic stroke.

Design, Setting, and Participants

A randomized, multicenter, open-label, blinded end point evaluation, comparative phase 2 trial was conducted from April 28, 2014, to December 7, 2015, at 14 academic medical centers in South Korea among patients with mild AF-related stroke within the previous 5 days who were deemed suitable for early anticoagulation. Analysis was performed on a modified intent-to-treat basis.

Interventions

Participants were randomized 1:1 to receive rivaroxaban, 10 mg/d for 5 days followed by 15 or 20 mg/d, or warfarin with a target international normalized ratio of 2.0-3.0, for 4 weeks.

Main Outcomes and Measures

The primary end point was the composite of new ischemic lesion or new intracranial hemorrhage seen on results of magnetic resonance imaging at 4 weeks. Primary analysis was performed in patients who received at least 1 dose of study medications and completed follow-up magnetic resonance imaging. Key secondary end points were individual components of the primary end point and hospitalization length.

Results

Of 195 patients randomized, 183 individuals (76 women and 107 men; mean [SD] age, 70.4 [10.4] years) completed magnetic resonance imaging follow-up and were included in the primary end point analysis. The rivaroxaban group (n = 95) and warfarin group (n = 88) showed no differences in the primary end point (47 [49.5%] vs 48 [54.5%]; relative risk, 0.91; 95% CI, 0.69-1.20; P = .49) or its individual components (new ischemic lesion: 28 [29.5%] vs 31 of 87 [35.6%]; relative risk, 0.83; 95% CI, 0.54-1.26; P = .38; new intracranial hemorrhage: 30 [31.6%] vs 25 of 87 [28.7%]; relative risk, 1.10; 95% CI, 0.70-1.71; P = .68). Each group had 1 clinical ischemic stroke, and all new intracranial hemorrhages were asymptomatic hemorrhagic transformations. Hospitalization length was reduced with rivaroxaban compared with warfarin (median, 4.0 days [interquartile range, 2.0-6.0 days] vs 6.0 days [interquartile range, 4.0-8.0]; P < .001).

Conclusions and Relevance

In mild AF-related acute ischemic stroke, rivaroxaban and warfarin had comparable safety and efficacy.

Trial Registration

clinicaltrials.gov Identifier: NCT02042534.

Circadian variations in laboratory measurements of coagulation assays after administration of rivaroxaban or warfarin in patients with nonvalvular atrial fibrillation

BACKGROUND

Although rivaroxaban has a relatively shorter half-life and peak and trough plasma concentrations throughout the day than warfarin, rivaroxaban has been found to be non-inferior to warfarin in preventing thromboembolic events in patients with nonvalvular atrial fibrillation (NVAF). We measured circadian variations in laboratory measurements of coagulation assays for chronic treatment with rivaroxaban or warfarin in patients with NVAF.

METHODS

We included 28 consecutive patients with NVAF who were treated with rivaroxaban (n=13) or warfarin (n=15). Blood samples were collected at 6 AM, 11 AM, and 3 PM on the same day and on the next morning at 6 AM. Prothrombin time (PT), international normalized ratio of the PT (PT-INR), activated partial thromboplastin time (APTT), prothrombin fragment 1+2 (F1+2), and protein C level/activity were measured in each patient.

RESULTS

PT and PT-INR were significantly and consistently lower, and the F1+2 and protein C level/activity were significantly and consistently higher throughout the day in rivaroxaban-treated patients than in warfarin-treated patients. Significant increases in PT and PT-INR were observed 3h after oral administration in the patients taking rivaroxaban in the morning, whereas, significant increases in the protein C level/activity were observed 3h after oral administration in the patients taking warfarin in the morning.

CONCLUSIONS

The protein C level/activity was significantly and consistently higher in the rivaroxaban-treated patients than in the warfarin-treated patients throughout the day, which was in contrast to the findings for other coagulation assays. These findings may partly explain the specific persistent anticoagulant effects of rivaroxaban even during the trough phase of the plasma concentration.

Individualized approaches to thromboprophylaxis in atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia worldwide. The prevalence of AF in persons older than 55 years is at least 33.5 million globally and is predicted to more than double in the next half-century. Anticoagulation, heart rate control, and heart rhythm control comprise the 3 main treatment strategies in AF. Anticoagulation is aimed at preventing debilitating stroke, systemic embolism, and associated mortality. Historically, anticoagulation in AF was achieved with a vitamin K antagonist such as warfarin, which is supported by evidence demonstrating reduced incident stroke and all-cause mortality. However, warfarin has unpredictable pharmacokinetics with many drug-drug interactions that require regular monitoring to ensure patients remain in the therapeutic anticoagulant range. Non-vitamin K antagonist oral anticoagulants including dabigatran, rivaroxaban, apixaban, and edoxaban provide a possible solution to these issues with their more predictable pharmacokinetics, rapid onset of action, and greater specificity. Results from large randomized, controlled trials indicate that these agents are at least noninferior to warfarin in prevention of stroke. These trials also demonstrate a consistently lower incidence of intracranial hemorrhage, almost always all life-threatening bleeds, and many forms of major bleeds with the possible exception of gastrointestinal and some other forms of mucosal bleeding, compared with warfarin. Patients with AF are a heterogeneous population with diverse risk of stroke and bleeding, and different subgroups respond differently to anticoagulation. Important clinical questions have arisen regarding optimal anticoagulation drug selection in distinct populations such as those with renal impairment, older age, coronary artery disease, and heart failure as well as those at particularly high risk for bleeding or thromboembolism. In this review, treatment strategies in AF management are discussed in the context of different individual subgroups of patients.

Risk of Gastrointestinal Bleeding with Rivaroxaban: A Comparative Study with Warfarin

Introduction. The risk of gastrointestinal (GI) bleeding with rivaroxaban has not been studied extensively. The aim of our study was to assess this risk in comparison to warfarin. Methods. We examined the medical records for patients who were started on rivaroxaban or warfarin from April 2011 to April 2013. Results. We identified 300 patients (147 on rivaroxaban versus 153 on warfarin). GI bleeding occurred in 4.8% patients with rivaroxaban when compared to 9.8% patients in warfarin group (p = 0.094). GI bleeding occurred in 8% with therapeutic doses of rivaroxaban (>10 mg/d) compared to 9.8% with warfarin (p = 0.65). Multivariate analysis showed that patients who were on rivaroxaban for ≤40 days had a higher incidence of GI bleeding than those who were on it for >40 days (OR = 2.8, p = 0.023). Concomitant use of dual antiplatelet agents was associated with increased risk of GI bleeding in the rivaroxaban group (OR = 7.4, p = 0.0378). Prior GI bleeding was also a risk factor for GI bleeding in rivaroxaban group (OR = 15.5). Conclusion. The incidence of GI bleeding was similar between rivaroxaban and warfarin. The risk factors for GI bleeding with rivaroxaban were the first 40 days of taking the drug, concomitant dual antiplatelet agents, and prior GI bleeding.

Clinical use of rivaroxaban: pharmacokinetic and pharmacodynamic rationale for dosing regimens in different indications

Target-specific oral anticoagulants have become increasingly available as alternatives to traditional agents for the management of a number of thromboembolic disorders. To date, the direct Factor Xa inhibitor rivaroxaban is the most widely approved of the new agents. The dosing of rivaroxaban varies and adheres to specific schedules in each of the clinical settings in which it has been investigated. These regimens were devised based on the results of phase II dose-finding studies and/or pharmacokinetic modeling, and were demonstrated to be successful in randomized, phase III studies. In most cases, the pharmacodynamic profile of rivaroxaban permits once-daily dosing. A once-daily dose is indicated for the prevention of venous thromboembolism (VTE) in patients undergoing hip or knee replacement surgery, the long-term prevention of stroke in patients with non-valvular atrial fibrillation, and the long-term secondary prevention of recurrent VTE. Twice-daily dosing is required in the acute phase of treatment in patients with VTE and in the combination of rivaroxaban with standard single or dual antiplatelet therapy for secondary prevention after acute coronary syndrome events. This article reviews the empirical and clinical rationale supporting the dose regimens of rivaroxaban in each clinical setting.

Pharmacokinetic and pharmacodynamic evaluation of rivaroxaban: considerations for the treatment of venous thromboembolism

Patients with deep vein thrombosis or pulmonary embolism are recommended to receive anticoagulation for acute treatment and secondary prevention of venous thromboembolism (VTE). Fast-acting direct oral anticoagulants, with or without parenteral heparin, have the potential to replace vitamin K antagonists in this setting. Rivaroxaban, a direct Factor Xa inhibitor, is approved in the European Union and the United States for the single-drug treatment of deep vein thrombosis and pulmonary embolism and the secondary prevention of recurrent VTE in adults. The approved rivaroxaban dose schedule (15 mg twice daily for 3 weeks followed by 20 mg once daily) was derived based on pharmacological data from the clinical development programme to achieve a strong antithrombotic effect in the acute treatment phase and address the need to balance efficacy and bleeding risk for long-term treatment with a once-daily dose in the maintenance phase. Data from dose-ranging studies, pharmacokinetic modelling and randomised phase III trials support the use of this regimen. Other direct oral anticoagulants have also shown favourable efficacy and safety compared with standard treatment, and apixaban (European Union) and dabigatran (European Union and United States) have been approved in this indication. There are practical aspects to rivaroxaban use that must be considered, such as treatment of patients with renal and hepatic impairment, drug–drug interactions, monitoring of effect and management of bleeding. This review discusses the derivation of the VTE treatment regimen for rivaroxaban, summarises the clinical data for rivaroxaban and other direct oral anticoagulants in VTE treatment, and considers the practical aspects of rivaroxaban use in this setting.

Clinical pharmacokinetic and pharmacodynamic profile of rivaroxaban

Rivaroxaban is an oral, direct Factor Xa inhibitor that targets free and clot-bound Factor Xa and Factor Xa in the prothrombinase complex. It is absorbed rapidly, with maximum plasma concentrations being reached 2-4 h after tablet intake. Oral bioavailability is high (80-100 %) for the 10 mg tablet irrespective of food intake and for the 15 mg and 20 mg tablets when taken with food. Variability in the pharmacokinetic parameters is moderate (coefficient of variation 30-40 %). The pharmacokinetic profile of rivaroxaban is consistent in healthy subjects and across a broad range of different patient populations studied. Elimination of rivaroxaban from plasma occurs with a terminal half-life of 5-9 h in healthy young subjects and 11-13 h in elderly subjects. Rivaroxaban produces a pharmacodynamic effect that is closely correlated with its plasma concentration. The pharmacokinetic and pharmacodynamic relationship for inhibition of Factor Xa activity can be described by an E max model, and prothrombin time prolongation by a linear model. Rivaroxaban does not inhibit cytochrome P450 enzymes or known drug transporter systems and, because rivaroxaban has multiple elimination pathways, it has no clinically relevant interactions with most commonly prescribed medications. Rivaroxaban has been approved for clinical use in several thromboembolic disorders.

Non-vitamin K antagonist oral anticoagulants in cardiovascular disease management: evidence and unanswered questions

WHAT IS KNOWN AND OBJECTIVE

Anticoagulation is important in the management of cardiovascular disorders; however, traditional anticoagulants such as heparins and vitamin K antagonists (VKAs) have limitations, including parenteral administration with the former and the need for coagulation monitoring and dose adjustments with the latter. Three non-VKA oral anticoagulants (OACs), dabigatran, rivaroxaban and apixaban, are available for the prevention of stroke in patients with atrial fibrillation (AF) and may change clinical practice. This article reviews current knowledge and important unanswered questions on the use of these agents in patients with cardiovascular disease.

METHODS

A literature search was performed using PubMed and the search terms dabigatran, rivaroxaban, apixaban, AF and acute coronary syndrome (ACS). Peer-reviewed, published clinical trials, review articles, relevant treatment guidelines and prescribing information documents were identified and reviewed for relevance.

RESULTS AND DISCUSSION

Dabigatran is an oral direct thrombin inhibitor; rivaroxaban and apixaban are oral direct Factor Xa inhibitors. These agents have a quicker onset and offset of action, more predictable pharmacokinetic and pharmacodynamic profiles, and fewer drug-drug interactions than VKAs, allowing use of fixed doses. For the prevention of stroke in patients with AF, the non-VKA OACs were either non-inferior or superior to warfarin with similar or improved bleeding profiles, particularly with respect to reductions in intracranial haemorrhage. In patients with ACS receiving dual antiplatelet therapy, the addition of rivaroxaban significantly reduced the rate of death from cardiovascular causes, myocardial infarction or stroke without increasing fatal bleeding, but led to higher rates of major bleeding. Dose reductions with non-VKA OACs are mandated in certain circumstances in patients with AF, such as moderate renal impairment. Contraindications include creatinine clearance <15 mL/min (<30 mL/min for dabigatran in Europe and Canada) and moderate or severe hepatic impairment, but patients can be transitioned to other anticoagulants if appropriate. It is unknown which non-VKA OAC is optimal for stroke prevention in patients with AF, although factors such as co-medications (e.g. dabigatran may be preferred if a patient is taking a co-medication that is a strong cytochrome P450 3A4 inhibitor) and renal function (rivaroxaban and apixaban depend less on renal clearance than dabigatran) will be important for individual patients. Addition of rivaroxaban to antiplatelet therapy for prevention of recurrent events in patients with recent ACS is approved in Europe for patients at the highest risk (with elevated cardiac biomarkers) and must take into account the increased risk of major bleeding. Although routine coagulation monitoring is not required, an understanding of which assays are appropriate for each non-VKA OAC and how they are affected is important. In a bleeding emergency, non-specific prohaemostatic agents are suggested to reverse the action of the non-VKA OACs, but more clinical data are needed.

WHAT IS NEW AND CONCLUSION

Non-VKA OACs provide similar or improved efficacy and, on current evidence, improved safety. They provide greater convenience, compared with traditional anticoagulants for the prevention of stroke in patients with AF. Rivaroxaban may be of benefit to selected high-risk patients with ACS. Selection of the most appropriate non-VKA OAC will depend on individual patient factors.

Rivaroxaban and other non-vitamin K antagonist oral anticoagulants in the emergency treatment of thromboembolism

Pulmonary embolism (PE) is potentially fatal and often requires emergency management. Because PE associated with shock and/or hypotension carries a high risk of sudden death, emergency clinicians must rapidly make a diagnosis and initiate appropriate therapeutic strategies, usually involving anticoagulant treatment. Traditional anticoagulants, such as heparins and vitamin K antagonists, although effective and recommended by guidelines, are associated with limitations. Several targeted, orally administered anticoagulants that may overcome some of these constraints have been developed recently and undergone analysis in randomised, phase III clinical trials. Rivaroxaban, a direct factor Xa inhibitor, was non-inferior to standard therapy with enoxaparin plus a vitamin K antagonist for the prevention of recurrent, symptomatic venous thromboembolism (VTE) in patients with acute PE and led to a 50% reduction in major bleeding. Dabigatran, a direct thrombin inhibitor, was also non-inferior to standard therapy for the prevention of recurrent VTE or VTE-related death when given after a parenteral anticoagulant and had a similar incidence of major bleeding. The results of a phase III study of apixaban, another direct factor Xa inhibitor, for the acute treatment of VTE are expected in the near future. Rivaroxaban is now approved in Europe and the US for the treatment of acute PE and prevention of recurrent VTE. This article reviews the current guidance on the treatment of PE with special focus on the emergency setting, and considers data regarding rivaroxaban and the other non-vitamin K antagonist oral anticoagulants and their potential role, including patients who are and are not appropriate for treatment with these agents. Issues such as drug interactions, reversal of anticoagulant effect and coagulation monitoring are also discussed.

Rivaroxaban: an oral factor Xa inhibitor

BACKGROUND

Currently available anticoagulants utilized for venous thromboembolism (VTE) treatment and prevention and stroke prevention in patients with atrial fibrillation (AF) have proven effectiveness but are not optimally utilized because of barriers such as the need for subcutaneous administration and requisite routine laboratory monitoring. Rivaroxaban, a novel oral Xa inhibitor, is an alternative to standard therapies utilized for VTE prevention after elective orthopedic surgery, primary and secondary stroke prevention in nonvalvular AF, VTE treatment after an acute VTE event, and secondary prevention after the acute coronary syndromes (ACS).

OBJECTIVE

This article reviews the pharmacology, efficacy, and tolerability of rivaroxaban for VTE prophylaxis in post-orthopedic surgery and medically ill patients, stroke prevention in nonvalvular AF, adjunctive therapy in patients with ACS, and VTE treatment.

METHODS

International Pharmaceutical Abstracts and EMBASE were searched for English-only clinical trials and reviews published between 1970 and March 15, 2012. PubMed was searched for articles published between 1970 and June 30, 2012. Additional trials and reviews were identified from the citations of published articles.

RESULTS

Eighty-nine publications were identified: 10 clinical trials and 1 meta-analysis were used to obtain efficacy and tolerability data, and 1 analysis of pooled data from the clinical trials was included; 17 pharmacokinetic, pharmacodynamic, and drug-drug interaction studies were included; and 5 cost-analyses were reviewed. These data showed rivaroxaban to be noninferior to enoxaparin for thromboprophylaxis of VTE after total knee and total hip replacement surgery. It was also shown to be noninferior to vitamin K antagonist therapy for primary and recurrent stroke prevention in nonvalvular AF as well as for the treatment of VTE after an acute deep vein thrombosis or pulmonary embolism. It also showed benefit in lowering the risk for major adverse cardiovascular events after ACS. Differences in major bleeding rates were not statistically significant between rivaroxaban and comparators across the various studies, with the exception of ACS, in which there were higher rates of non-coronary artery bypass graft surgery related bleeding and intracranial hemorrhage.

CONCLUSIONS

Based on the findings of the studies reported in this review, rivaroxaban is an effective option for the prevention of VTE after orthopedic surgery, stroke prevention for nonvalvular AF, and treatment of VTE. At this time, rivaroxaban cannot be recommended for secondary risk reduction after ACS because of the increased bleeding risk.

Rivaroxaban and other novel oral anticoagulants: pharmacokinetics in healthy subjects, specific patient populations and relevance of coagulation monitoring

Unlike traditional anticoagulants, the more recently developed agents rivaroxaban, dabigatran and apixaban target specific factors in the coagulation cascade to attenuate thrombosis. Rivaroxaban and apixaban directly inhibit Factor Xa, whereas dabigatran directly inhibits thrombin. All three drugs exhibit predictable pharmacokinetic and pharmacodynamic characteristics that allow for fixed oral doses in a variety of settings. The population pharmacokinetics of rivaroxaban, and also dabigatran, have been evaluated in a series of models using patient data from phase II and III clinical studies. These models point towards a consistent pharmacokinetic and pharmacodynamic profile, even when extreme demographic factors are taken into account, meaning that doses rarely need to be adjusted. The exception is in certain patients with renal impairment, for whom pharmacokinetic modelling provided the rationale for reduced doses as part of some regimens. Although not routinely required, the ability to measure plasma concentrations of these agents could be advantageous in emergency situations, such as overdose. Specific pharmacokinetic and pharmacodynamic characteristics must be taken into account when selecting an appropriate assay for monitoring. The anti-Factor Xa chromogenic assays now available are likely to provide the most appropriate means of determining plasma concentrations of rivaroxaban and apixaban, and specific assays for dabigatran are in development.

Novel oral anticoagulants: clinical pharmacology, indications and practical considerations

BACKGROUND

Novel oral anticoagulants are approved in several indications: rivaroxaban, apixaban, and dabigatran for the prevention of venous thromboembolism after elective hip or knee replacement surgery, and edoxaban for hip or knee replacement surgery and hip fracture surgery (in Japan only); rivaroxaban for the treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE), and prevention of recurrent DVT and PE; and rivaroxaban, apixaban, and dabigatran for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation. These agents overcome some limitations of traditional anticoagulants, are suggested to have no requirement for routine coagulation monitoring, and are administered orally. Rivaroxaban, apixaban, and dabigatran have different pharmacological characteristics, and guidance is needed on optimum doses and dosing intervals and the effects of renal or hepatic impairment, age, food, and other drugs. Dabigatran has stricter prescribing advice than rivaroxaban or apixaban for patients with moderate-to-severe renal impairment. All three drugs have restrictions on use in patients with hepatic impairment. Apixaban requires twice-daily dosing in all indications, whereas rivaroxaban and dabigatran are dosed once- or twice-daily depending on indication. Although head-to-head comparisons are lacking, the novel oral anticoagulants may show favorable cost-benefit relations compared with traditional vitamin K antagonists or no therapy.

AIM

This review summarizes the pharmacology of rivaroxaban, apixaban, edoxaban, and dabigatran, and the indications for which they are approved. Issues regarding the optimization of the use of these anticoagulants for the management of thromboembolic disorders will also be discussed.

Confirmation of model-based dose selection for a Japanese phase III study of rivaroxaban in non-valvular atrial fibrillation patients

This study was designed to confirm the appropriateness of the dose setting for a Japanese phase III study of rivaroxaban in patients with non-valvular atrial fibrillation (NVAF), which had been based on model simulation employing phase II study data. The previously developed mixed-effects pharmacokinetic/pharmacodynamic (PK-PD) model, which consisted of an oral one-compartment model parameterized in terms of clearance, volume and a first-order absorption rate, was rebuilt and optimized using the data for 597 subjects from the Japanese phase III study, J-ROCKET AF. A mixed-effects modeling technique in NONMEM was used to quantify both unexplained inter-individual variability and inter-occasion variability, which are random effect parameters. The final PK and PK-PD models were evaluated to identify influential covariates. The empirical Bayes estimates of AUC and C(max) from the final PK model were consistent with the simulated results from the Japanese phase II study. There was no clear relationship between individual estimated exposures and safety-related events, and the estimated exposure levels were consistent with the global phase III data. Therefore, it was concluded that the dose selected for the phase III study with Japanese NVAF patients by means of model simulation employing phase II study data had been appropriate from the PK-PD perspective.

A novel μ-fluidic whole blood coagulation assay based on Rayleigh surface-acoustic waves as a point-of-care method to detect anticoagulants

A universal coagulation test that reliably detects prolonged coagulation time in patients, irrespective of the anticoagulant administered, has not been available to date. An easily miniaturised, novel μ-fluidic universal coagulation test employing surface acoustic waves (SAW) is presented here. SAW was employed to instantly mix and recalcify 6 μl citrated whole blood and image correlation analysis was used to quantify clot formation kinetics. The detection of clinically relevant anticoagulant dosing with old anticoagulants (unfractionated heparin, argatroban) and new anticoagulants (dabigatran, rivaroxaban) has been tested and compared to standard plasma coagulation assays. The applicability of this novel method has been confirmed in a small patient population. Coagulation was dose-proportionally prolonged with heparin, argatroban, dabigatran, and rivaroxaban, comparable to standard tests. Aspirin and clopidogrel did not interfere with the SAW-induced clotting time (SAW-CT), whereas the strong GPIIb/IIIa-inhibitor abciximab did interfere. Preliminary clinical data prove the suitability of the SAW-CT in patients being treated with warfarin, rivaroxaban, or dabigatran. The system principally allows assessment of whole blood coagulation in humans in a point-of-care setting. This method could be used in stroke units, emergency vehicles, general and intensive care wards, as well as for laboratory and home testing of coagulation.

Rivaroxaban in Nonvalvular Atrial Fibrillation

Each month, subscribers to The Formulary Monograph Service receive 5 to 6 well-documented monographs on drugs that are newly released or are in late phase 3 trials. The monographs are targeted to Pharmacy & Therapeutics Committees. Subscribers also receive monthly 1-page summary monographs on agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation/medication use evaluation (DUE/MUE) is also provided each month. With a subscription, the monographs are sent in print and are also available on-line. Monographs can be customized to meet the needs of a facility. Subscribers to The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X. A drug class review is now published monthly with The Formulary Monograph Service. Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The April 2012 monograph topics are on ivacaftor, vismodegib, axitinib, glucarpidase, and loxapine inhalation. The DUE/MUE is on glucarpidase.

Oral anticoagulant therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

The objective of this article is to summarize the published literature concerning the pharmacokinetics and pharmacodynamics of oral anticoagulant drugs that are currently available for clinical use and other aspects related to their management.

METHODS

We carried out a standard review of published articles focusing on the laboratory and clinical characteristics of the vitamin K antagonists; the direct thrombin inhibitor, dabigatran etexilate; and the direct factor Xa inhibitor, rivaroxaban

RESULTS

The antithrombotic effect of each oral anticoagulant drug, the interactions, and the monitoring of anticoagulation intensity are described in detail and discussed without providing specific recommendations. Moreover, we describe and discuss the clinical applications and optimal dosages of oral anticoagulant therapies, practical issues related to their initiation and monitoring, adverse events such as bleeding and other potential side effects, and available strategies for reversal.

CONCLUSIONS

There is a large amount of evidence on laboratory and clinical characteristics of vitamin K antagonists. A growing body of evidence is becoming available on the first new oral anticoagulant drugs available for clinical use, dabigatran and rivaroxaban.