Integrated Population Pharmacokinetic Analysis of Rivaroxaban Across Multiple Patient Populations

Controversies and challenges of anticoagulation therapy in obesity

INTRODUCTION

The relationship between anticoagulation efficacy and safety in obesity is complex and can vary between degrees of obesity and anticoagulant choice. Indeed, patients at extremes of body weight were under-represented in randomized trials. Additionally, the possibility of an 'obesity paradox' has been raised in atrial fibrillation, describing decreased thromboembolic risk in obese patients.

AREAS COVERED

We explore the current literature on anticoagulation in obesity, specifically with regard to efficacy in atrial fibrillation, efficacy in venous thromboembolism, and bleeding risk. Pharmacodynamic and pharmacokinetic considerations are also discussed.

EXPERT OPINION

As a class, direct oral anticoagulants are comparable to vitamin-K antagonists in preventing and treating thromboembolism in overweight and obese patients, whilst not increasing bleeding risk.

Population pharmacokinetics and pharmacodynamics of edoxaban in pediatric patients

Edoxaban is an orally active inhibitor of activated factor X (FXa). Population pharmacokinetic (PK) and pharmacodynamic (PD) analyses were performed to characterize the PK and PK-PD relationships of edoxaban in pediatric patients to identify the covariates that may contribute to inter-subject variability in PK and PD of edoxaban in pediatric patients, and to compare the PK and PD data between pediatric and adult patients. The pediatric PK of edoxaban was best described by a two-compartment model with transit compartments, first-order oral absorption, and linear elimination. The estimated glomerular filtration rate (eGFR), body weight, and post-menstrual age were the significant covariates explaining variability in edoxaban PK among pediatric patients. A function based on renal maturation was applied to edoxaban clearance. The clearance for a 70 kg patient with an eGFR of 110 mL/min/1.73 m2 was estimated to be 42.9 L/h (CV ~ 31.8%). PK simulation showed that exposures across five pediatric age groups were comparable to that in adult patients receiving 60 mg once daily dose. The PK-PD relationship for anti-factor Xa was best fit with an Emax (8.65 IU/mL) model with an EC50 of 631 ng/mL. The PK-PD relationships for activated partial thromboplastin time and prothrombin time were best fit with linear models (slopes of 0.0467, and 0.0415 s mL/ng, respectively). In addition, due to the small number of efficacy and safety events, an exploratory analysis did not detect a correlation between efficacy events (recurrent venous thromboembolism) or safety events (clinically relevant bleeding) and edoxaban exposure.

Handling delayed or missed direct oral anticoagulant doses: model-informed individual remedial dosing

ABSTRACT

Nonadherence to direct oral anticoagulant (DOAC) pharmacotherapy may increase the risk of thromboembolism or bleeding, and delayed or missed doses are the most common types of nonadherence. Current recommendations from regulatory agencies or guidelines regarding this issue lack evidence and fail to consider individual differences. This study aimed to develop individual remedial dosing strategies when the dose was delayed or missed for DOACs, including rivaroxaban, apixaban, edoxaban, and dabigatran etexilate. Remedial dosing regimens based on population pharmacokinetic (PK)-pharmacodynamic (PD) modeling and simulation strategies were developed to expeditiously restore drug concentration or PD biomarkers within the therapeutic range. Population PK-PD characteristics of DOACs were retrieved from previously published literature. The effects of factors that influence PK and PD parameters were assessed for their impact on remedial dosing regimens. A web-based dashboard was established with R-shiny to recommend remedial dosing regimens based on patient traits, dosing schedules, and delay duration. Addressing delayed or missed doses relies on the delay time and specific DOACs involved. Additionally, age, body weight, renal function, and polypharmacy may marginally affect remedial strategies. The proposed remedial dosing strategies surpass current recommendations, with less deviation time beyond the therapeutic range. The online dashboard offers quick and convenient solutions for addressing missed or delayed DOACs, enabling individualized remedial dosing strategies based on patient characteristics to mitigate the risks of bleeding and thrombosis.

Exposure Matching-Based Pediatric Dose Selection for Drugs with Renal Excretion - Lessons Learned from Pediatric Development of Direct Oral Anticoagulants

The pediatric clinical development programs of the direct oral anticoagulants (DOACs) edoxaban, rivaroxaban, and dabigatran have recently been completed, with apixaban close to the finish line. One common pharmacokinetic (PK) characteristic of these four DOACs is that renal excretion contributes 27% or more in their elimination, resulting in age-dependent drug clearance in both pediatric and adult subjects. Several lessons have been learned from adult exposure matching and pediatric dose selection for DOACs. The main goal of this tutorial is to provide an informed perspective on pediatric dose selection for renally excreted drugs, using these four DOACs as case examples. This tutorial is organized into seven steps: (1) consideration of age-related differences in disease and response to treatment; (2) consideration of age-related differences in drug absorption, distribution, metabolism, and excretion; (3) selection of the reference adult population and exposure for pediatric exposure matching; (4) prediction of pediatric clearance and pediatric dose selection based on data from young adults; (5) conduct and design of efficient pediatric PK and pharmacodynamic (PD) studies that inform dose selection; (6) assessment of exposure matching and dose adjustment using population PK simulation; (7) evaluation of the need for dose adjustment in pediatric sub-populations.

Full-dose rivaroxaban in patients with a history of bariatric surgery: bridging the knowledge gap through a phase 1 study

BACKGROUND

Bariatric surgery (BS) induces significant changes in gastrointestinal anatomy, potentially influencing the pharmacokinetics of orally administered drugs such as rivaroxaban.

OBJECTIVES

This phase 1 study aimed to assess the pharmacokinetics and safety of full-dose rivaroxaban in post-BS patients.

METHODS

The ABSORB (Rivaroxaban Pharmacokinetics and Pharmacodynamics After Bariatric Surgery and in Morbid Obesity) study was a single-center, nonrandomized, multiple-dose, parallel-design bioequivalence trial. Adult patients with stable weight after Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) were compared with subjects with class III obesity and healthy controls. Participants received 20 mg of rivaroxaban daily for 8 days.

RESULTS

Post-BS patients exhibited altered rivaroxaban pharmacokinetics, suggesting reduced absorption. Mean area under the concentration-time curve from time 0 to 24 hours after the first dose (RYGB, 1806.8 ng.h/mL; SG, 1648.9 ng.h/mL) was lower compared with that in controls (1893.5 ng.h/mL). At steady state, the area under the concentration-time curve values remained lower in BS groups (RYGB, 2129.9 ng.h/mL; SG, 1946.4 ng.h/mL) than in controls (2224.8 ng.h/mL). The maximum concentration after the first dose was lower in post-RYGB subjects (214.9 ng/mL) than in controls (264.1 ng/mL). This difference was less pronounced at steady state (RYGB, 256.9 ng/mL vs controls, 288.8 ng/mL). Neither BS group met bioequivalence criteria compared with controls, whereas the group with class III obesity met bioequivalence criteria compared with controls at steady state.

CONCLUSION

Rivaroxaban displayed minor pharmacokinetic variations in post-BS patients. Given reported interindividual variability in the general population, these variations are unlikely to be of clinical significance. Our findings support rivaroxaban use in BS patients, emphasizing the need for further research in this area.

Efficacy and Safety of Direct Oral Anticoagulants versus Warfarin in Obese Patients (BMI ≥ 30 kg/m2) with Atrial Fibrillation or Venous Thromboembolism: An Updated Systematic Review and Meta-Analysis

Background: Real-world data show limited utilization of direct oral anticoagulants (DOACs) in obese patients (body mass index [BMI] ≥ 30 kg/m2) due to concerns regarding their efficacy and safety in this demographic. Aim: This review aimed to consolidate current evidence on the efficacy and safety of DOACs versus warfarin in obese patients with non-valvular atrial fibrillation (AF) or venous thromboembolism (VTE). The primary efficacy outcome assessed a composite of all-cause mortality, stroke, systemic embolism (SE), and myocardial infarction (MI). Methods: A systematic search was conducted in MEDLINE, SCOPUS, and Cochrane databases from inception to December 28, 2023. Data were synthesized using random-effects meta-analysis. Results: A total of 35 studies involving 434,320 participants were analyzed. DOAC use was associated with a significant reduction in the risk of the composite outcome (RR = 0.80, 95% CI [0.65, 0.98], I2 = 95%), hemorrhagic stroke (RR = 0.58, 95% CI [0.38, 0.88], I2 = 92%), major bleeding (RR = 0.76, 95% CI [0.63, 0.92], I2 = 94%), gastrointestinal bleeding (RR = 0.59, 95% CI [0.49, 0.72], I2 = 88%), and intracranial bleeding (RR = 0.45, 95% CI [0.34, 0.60], I2 = 44%) compared to warfarin. A non-significant benefit of DOACs was observed for all-cause mortality, MI, the composite of stroke or SE, ischemic stroke, SE, VTE, and minor bleeding compared to warfarin. Subgroup analysis indicated no significant effect modification based on the indication for anticoagulation or study design. Conclusions: DOACs demonstrated a favorable efficacy and safety profile in obese individuals compared to warfarin.

Pharmacokinetics of single-dose rivaroxaban under fed state in obese vs. non-obese subjects: An open-label controlled clinical trial (RIVOBESE-PK)

The evidence of rivaroxaban's pharmacokinetics in obese compared with non-obese populations remains inconclusive. We aimed to compare the pharmacokinetic profile of rivaroxaban between obese and non-obese populations under fed state. Participants who met the study's eligibility criteria were assigned into one of two groups: obese (body mass index ≥35 kg/m2) or non-obese (body mass index 18.5-24.9 kg/m2). A single dose of rivaroxaban 20 mg was orally administered to each participant. Nine blood samples over 48 h, and multiple urine samples over 18 h were collected and analyzed for rivaroxaban concentration using ultra-performance liquid chromatography coupled with tandem mass detector. Pharmacokinetic parameters were determined using WinNonlin software. Thirty-six participants were recruited into the study. No significant changes were observed between obese and non-obese participants in peak plasma concentration, time to reach peak plasma concentration, area under the plasma concentration-time curve over 48 h or to infinity, elimination rate constant, half-life, apparent volume of distribution, apparent clearance, and fraction of drug excreted unchanged in urine over 18 h. Rivaroxaban's exposure was similar between the obese and non-obese subjects, and there were no significant differences in other pharmacokinetic parameters between the two groups. These results suggest that dose adjustment for rivaroxaban is probably unwarranted in the obese population.

Population pharmacokinetics of rivaroxaban in Chinese deep vein thrombosis patients and the exposure simulation for dosing recommendation

This study aimed to develop a population pharmacokinetic (PPK) model for rivaroxaban and establish a model-based dosing guideline tailored to Chinese patients with deep vein thrombosis (DVT). A nonlinear mixed-effects modeling approach was employed using Phoenix NLME 7.0 software to construct the PPK model for rivaroxaban. The PK of rivaroxaban was adequately characterized through a one-compartment model. Monte Carlo simulations were employed to formulate dosing guidelines applicable to different patient subgroups. Data from 60 Chinese DVT patients yielded 217 rivaroxaban plasma concentrations for analysis. The apparent clearance (CL/F) of rivaroxaban was found to be significantly influenced by the estimated glomerular filtration rate (eGFR), identified as a major covariate. Based on Monte Carlo simulations, for the acute DVT treatment, a regimen of 15 mg, 10 mg, or 5 mg twice daily was associated with the highest total probability target attainment (PTAtotal) in patients with normal, mildly impaired, or moderately impaired renal function, respectively. For the continued DVT treatment, a regimen of 20 mg, 15 mg, or 5 mg once daily exhibited the maximum PTAtotal in patients with normal, mildly impaired, or moderately impaired renal function, respectively. The recommendation label dose achieved the PK target in those with normal renal function. However, for patients with mild or moderate renal impairment, dose adjustments below the label recommendation might be necessary. The PPK model associated CL/F with the covariate eGFR. Utilizing the PPK model, a dosage regimen table was constructed to offer tailored dosing recommendations for Chinese DVT patients.

An extension of biorelevant fed-state dissolution tests to clinical pharmacokinetics - A study on gastrointestinal factors influencing rivaroxaban exposure and efficacy in atrial fibrillation patients

A direct oral anticoagulant rivaroxaban fails to prevent stroke and systemic embolism in one-to-several percent of patients with nonvalvular atrial fibrillation (NVAF), but the reasons are unknown. The study used semi-mechanistic in vitro-in vivo prediction (IVIVP) modeling to explore the reasons for ineffective thrombosis prevention in NVAF patients. Steady-state drug concentrations in plasma were measured at 0 h (Ctrough), 3 h (C3h), and 12 h post-dosing in thirty-four patients treated with 20 mg rivaroxaban daily. The clinical data were compared against "virtual twins" generated with a novel IVIVP model that combined drug dissolution modeling, mechanistic description of gastric drug transit, and population pharmacokinetics defining the variability of drug disposition. The nonresponders had significantly lower C3h and Ctrough than the responders (p < 0.001) and the covariates included in the population pharmacokinetic submodel did not fully explain this difference. Simulations involving varied gastrointestinal parameters in the "virtual twins" revealed that lower small intestinal effective permeability (Peff), rather than a slower stomach emptying rate, could explain low rivaroxaban exposure in the nonresponders. IVIVP modeling was effectively used for exploring pharmacotherapy failure. Low Peff, found as a major determinant of ineffective rivaroxaban treatment, encourages further research to find (pato)physiological factors influencing suboptimal absorption.

Insights into the Pharmacokinetics and Pharmacodynamics of Direct Oral Anticoagulants in Older Adults with Atrial Fibrillation: A Structured Narrative Review

Older adults, the fastest growing population, represent almost 50% of all users of direct oral anticoagulants (DOACs). Unfortunately, we have very little relevant pharmacological and clinical data on DOACs, especially in older adults with geriatric profiles. This is highly relevant as pharmacokinetics and pharmacodynamics (PK/PD) often differ substantially in this population. Hence, we need to obtain a better understanding of the PK/PD of DOACs in older adults, to ensure appropriate treatment. This review summarises the current insights into PK/PD of DOACs in older adults. A search was undertaken up to October 2022 to identify PK/PD studies of apixaban, dabigatran, edoxaban, and rivaroxaban, that included older adults aged ≥ 75 years. This review identified 44 articles. Older age alone did not influence exposure of edoxaban, rivaroxaban and dabigatran, while apixaban peak concentrations were 40% higher in older adults than in young volunteers. Nevertheless, high interindividual variability in DOAC exposure in older adults was noted, which can be explained by distinctive older patient characteristics, such as kidney function, changes in body composition (especially reduced muscle mass), and co-medication with P-gp inhibitors, which is in line with the current dosing reduction criteria of apixaban, edoxaban, and rivaroxaban. Dabigatran had the largest interindividual variability among all DOACs since its dose adjustment criterion is only age, and thus it is not a preferable option. Additionally, DOAC exposure, which fell outside of on-therapy ranges, was significantly related to stroke and bleeding events. No definite thresholds linked to these outcomes in older adults have been established.

Transferability of Published Population Pharmacokinetic Models for Apixaban and Rivaroxaban to Subjects with Obesity Treated for Venous Thromboembolism: A Systematic Review and External Evaluations

Apixaban and rivaroxaban have first-line use for many patients needing anticoagulation for venous thromboembolism (VTE). The pharmacokinetics of these drugs in non-obese subjects have been extensively studied, and, while changes in pharmacokinetics have been documented in obese patients, data remain scarce for these anticoagulants. The aim of this study was to perform an external validation of published population pharmacokinetic (PPK) models of apixaban and rivaroxaban in a cohort of obese patients with VTE. A literature search was conducted in the PubMed/MEDLINE, Scopus, and Embase databases following the PRISMA statement. External validation was performed using MonolixSuite software, using prediction-based and simulation-based diagnostics. An external validation dataset from the university hospitals of Brest and Rennes, France, included 116 apixaban pharmacokinetic samples from 69 patients and 121 rivaroxaban samples from 81 patients. Five PPK models of apixaban and 16 models of rivaroxaban were included, according to the inclusion criteria of the study. Two of the apixaban PPK models presented acceptable performances, whereas no rivaroxaban PPK model did. This study identified two published models of apixaban applicable to apixaban in obese patients with VTE. However, none of the rivaroxaban models evaluated were applicable. Dedicated studies appear necessary to elucidate rivaroxaban pharmacokinetics in this population.

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.

Pharmacokinetics and Dosing Regimens of Direct Oral Anticoagulants in Morbidly Obese Patients: An Updated Literature Review

Data on the impact of morbid obesity (body mass index [BMI] ≥ 40 kg/m²) on the pharmacokinetics (PK), pharmacodynamics (PD) of direct oral anticoagulants (DOACs) are relatively limited, making it difficult to design optimal dosing regimens in morbidly obese patients.To review literature on PK/PD profile, efficacy, and safety of DOACs in venous thromboembolism (VTE) and nonvalvular atrial fibrillation (AF) patients with morbid obesity and make recommendations regarding optimal dosing regimens in these patient populations.A detailed literature search was conducted (from inception to June 22, 2022) for relevant articles involving PK/PD and clinical data on DOACs use in morbidly obese patients with VTE or AF, or healthy volunteers.A total of 28 studies were identified. DOAC-specific PK variations and clinical outcomes have been observed. Obesity may have a modest effect on PK/PD of dabigatran, apixaban, or rivaroxaban. Dabigatran was effective in AF patients with morbid obesity but might increase the risk of gastrointestinal bleeding. Standard dosing of apixaban or rivaroxaban is effective and safe for VTE and AF patients with morbid obesity. Trough edoxaban concentration and anti-Xa activity were similar in different BMI groups (18.5 to >40 kg/m²), and standard dosing of edoxaban may be effective and safe for AF patients.Current evidence suggests dabigatran should be used with caution in patients with AF as it might increase the risk of gastrointestinal bleeding; Standard dosing of apixaban or rivaroxaban can be used in VTE or AF patients; Standard dosing of edoxaban may be considered in AF patients.

Management of venous thromboembolism in morbidly obese patients: a 10-year review

Obesity is a known risk factor for venous thromboembolism (VTE) and poses a unique set of challenges in anticoagulation management. We report a 10-year experience of VTE management in morbidly obese patients. We conducted a retrospective analysis of VTE presentations to Northern Health, Victoria, Australia, from January 2011 to December 2020, with median follow-up of 44 months. Morbidly obese patients (defined as weighing > 120 kg) were compared to those ≤ 120 kg. Patients with active malignancy were excluded. 194 VTE cases with weight > 120 kg were compared to 2168 cases weighing ≤ 120 kg. Patients > 120 kg were more likely to present with unprovoked VTE (59.3% vs. 45.2%, p < 0.001) and major VTE (74.7% vs. 67.4%, p = 0.028). Overall, patients > 120 kg were more likely to develop VTE recurrence after anticoagulation cessation (7.80 vs. 3.92 per 100-patient-years, HR 1.97, 95%CI 1.29-3.00), while there were no significant differences in major bleeding or 30-day all-cause mortality. There were no significant differences in outcomes in patients > 120 kg treated with warfarin compared to direct oral anticoagulants (DOAC), or when comparing those treated with an uncapped (1 mg/kg BD) vs. capped (< 1 mg/kg) enoxaparin dosing regimen. Morbid obesity is associated with increased clot burden at presentation and VTE recurrence following anticoagulation cessation, without significant differences in bleeding compared to those ≤ 120 kg. There were no significant differences in morbidly obese patients' outcomes when treated with warfarin or DOAC, or when treated with an uncapped or capped enoxaparin dosing strategy. Larger randomised controlled trials evaluating the safety of DOACs and different enoxaparin dosing strategies in patients > 120 kg are warranted.

Challenges and Possible Solutions to Direct-Acting Oral Anticoagulants (DOACs) Dosing in Patients with Extreme Bodyweight and Renal Impairment

This article aims to highlight the dosing issues of direct oral anticoagulants (DOACs) in patients with renal impairment and/or obesity in an attempt to develop solutions employing advanced data-driven techniques. DOACs have become widely accepted by clinicians worldwide because of their superior clinical profiles, more predictable pharmacokinetics, and hence more convenient dosing relative to other anticoagulants. However, the optimal dosing of DOACs in extreme bodyweight  patients and patients with renal impairment is difficult to achieve using the conventional dosing approach. The standard dosing approach (fixed-dose) is based on limited data from clinical studies. The existing formulae (models) for determining the appropriate doses for these patient groups leads to suboptimal dosing. This problem of mis-dosing is worsened by the lack of standardized laboratory parameters for monitoring the exposure to DOACs in renal failure and extreme bodyweight patients. Model-informed precision dosing (MIPD) encompasses a range of techniques like machine learning and pharmacometrics modelling, which could uncover key variables and relationships as well as shed more light on the pharmacokinetics and pharmacodynamics of DOACs in patients with extreme bodyweight or renal impairment. Ultimately, this individualized approach-if implemented in clinical practice-could optimise dosing for the DOACs for better safety and efficacy.

Population Pharmacokinetics and Hemorrhagic Risk Analysis of Rivaroxaban in Elderly Chinese Patients With Nonvalvular Atrial Fibrillation

Rivaroxaban is a popular direct factor Xa inhibitor used for anticoagulation therapy in patients with nonvalvular atrial fibrillation (NVAF). The aim of this study was to establish a population pharmacokinetic (PPK) model for rivaroxaban in elderly Chinese patients with nonvalvular atrial fibrillation, evaluate precision dosing regimens, and analyze hemorrhagic risk after rivaroxaban treatment. A 1-compartment population PK model with estimated glomerular filtration rate (eGFR), total bilirubin (TBIL), and ABCB1 rs1045642 as major covariates for apparent clearance was developed using the nonlinear mixed-effects model (NONMEM). A Monte Carlo simulation was performed to evaluate various dosing schemes and different levels of covariates for the target range of therapeutic drug-monitoring concentrations (C_max,ss and C_min,ss ). The exposure to rivaroxaban was simulated and assessed through hemorrhagic risk evaluation. The results showed that the average probability of target attainment (PTA) for optimal dosing regimens with different covariate levels for the targeted C_max,ss and C_min,ss were 29.35% to 31.3% and 64.91% to 65.8%, respectively. A dosage of 10 mg of rivaroxaban in elderly Chinese patients with normal renal and liver function was appropriate. The area under the concentration-time curve estimated over 24 hours with precision dosing at steady state (AUC_24,ss ) was statistically significantly associated with an increased risk of bleeding events (OR 1.0006, 95%CI 1.0003 to 1.001, P < .0001), and the bleeding risk increased by 1.82-fold for every 1000 μg*h/L increase in AUC_24,ss . A lower dose is recommended for elderly patients with renal impairment to avoid overexposure and bleeding events. The PPK model could inform individualized dosing for elderly Chinese patients with nonvalvular atrial fibrillation receiving rivaroxaban anticoagulation therapy.

Leveraging a Previously Published Population Pharmacokinetic Model to Predict Rivaroxaban Exposure in Real-World Patients

Population pharmacokinetic (PK)/pharmacodynamic models are commonly used to inform drug dosing; however, often real-world patients are not well represented in the clinical trial population. We sought to determine how well dosing recommended in the rivaroxaban drug label results in exposure for real-world patients within a reference area under the concentration-time curve (AUC) range. To accomplish this, we assessed the utility of a prior published rivaroxaban population PK model to predict exposure in real-world patients. We used the model to predict rivaroxaban exposure for 230 real-world patients using 3 methods: (1) using patient phenotype information only, (2) using individual post hoc estimates of clearance from the prior model based on single PK samples of rivaroxaban collected at steady state without refitting of the prior model, and (3) using individual post hoc estimates of clearance from the prior model based on PK samples of rivaroxaban collected at steady state after refitting of the prior model. We compared the results across 3 software packages (NONMEM, Phoenix NLME, and Monolix). We found that while the average patient-assigned dosing per the drug label will likely result in the AUC falling within the reference range, AUC for most individual patients will be outside the reference range. When comparing post hoc estimates, the average pairwise percentage differences were all <10% when comparing the software packages, but individual pairwise estimates varied as much as 50%. This study demonstrates the use of a prior published rivaroxaban population PK model to predict exposure in real-world patients.

Trough Concentration Deficiency of Rivaroxaban in Patients With Nonvalvular Atrial Fibrillation Leading to Thromboembolism Events

ABSTRACT

This retrospective study investigated factors influencing the steady-state trough concentrations (C trough ) of rivaroxaban in patients with nonvalvular atrial fibrillation (NVAF). We retrieved data from patients with NAVF who first started rivaroxaban anticoagulation at the Fujian Provincial Hospital from October 2017 to October 2020 through the electronic medical record system. Patients were followed for 1 year after the first dose of rivaroxaban, and the primary efficacy and safety end points were recorded. All follow-up visits were completed by October 2021. A C trough of <12 ng/mL was defined as C trough deficiency. Factors that influenced rivaroxaban C trough deficiency were investigated using multivariate binary logistic regression analysis. Kaplan-Meier survival curve analysis was used to determine differences between C trough deficiency and event-free survival. A total of 167 patients with NVAF were enrolled in the study, including 113 men and 54 women, with an average (± SD) age of 70.40 ± 12.46 years. High albumin levels were an independent protective factor against C trough deficiency (odds ratio, 0.932; P = 0.031). C trough deficiency was associated with the probability of freedom from thrombotic events ( P = 0.004); however, there were no significant differences in the probability of freedom from bleeding events ( P > 0.05). In conclusion, among the variables studied, a low albumin level was the main contributor to C trough deficiency. Rivaroxaban C trough deficiency also increased thrombotic events, but this was not associated with hemorrhagic events in Chinese patients with NVAF.

Population Pharmacokinetics and Dose Optimization Based on Renal Function of Rivaroxaban in Thai Patients with Non-Valvular Atrial Fibrillation

Low-dose rivaroxaban has been used in Asian patients with direct oral anticoagulants (DOACs) eligible for atrial fibrillation (AF). However, there are few pharmacokinetic (PK) data in Thai patients to support precise dosing. This study aimed to develop a population PK model and determine the optimal rivaroxaban doses in Thai patients. A total of 240 Anti-Xa levels of rivaroxaban from 60 Thai patients were analyzed. A population PK model was established using the nonlinear mixed-effect modeling approach. Monte Carlo simulations were used to predict drug exposures at a steady state for various dosages. Proportions of patients having rivaroxaban exposure within typical exposure ranges were determined. A one-compartment model with first-order absorption best described the data. Creatinine clearance (CrCl) and body weight significantly affected CL/F and V/F, respectively. Regardless of body weight, a higher proportion of patients with CrCl < 50 mL/min receiving the 10-mg once-daily dose had rivaroxaban exposures within the typical exposure ranges. In contrast, a higher proportion of patients with CrCl ≥ 50 mL/min receiving the 15-mg once-daily dose had rivaroxaban exposures within the typical exposure ranges. The study’s findings suggested that low-dose rivaroxaban would be better suited for Thai patients and suggested adjusting the medication’s dose in accordance with renal function.

Model‐informed bridging of rivaroxaban doses for thromboprophylaxis in pediatric patients aged 9 years and older with congenital heart disease

Rivaroxaban is approved in various regions for the treatment of acute venous thromboembolism (VTE) in children aged between 0 and 18 years and was recently investigated for thromboprophylaxis in children aged between 2 and 8 years (with body weights <30 kg) with congenital heart disease who had undergone the Fontan procedure. In the absence of clinical data, rivaroxaban doses for thromboprophylaxis in post‐Fontan children aged 9 years and older or ≥30 kg were derived by a bridging approach that used physiologically‐based pharmacokinetic (PBPK) and population pharmacokinetic (popPK) models based on pharmacokinetic (PK) data from 588 pediatric patients and from adult patients who received 10 mg once daily for thromboprophylaxis after major orthopedic surgeries as a reference. Both models showed a tendency toward underestimating rivaroxaban exposure in post‐Fontan patients aged between 2 and 5 years but accurately described rivaroxaban PK in post‐Fontan patients aged between 5 and 8 years. Under the assumption that hepatic function is not impaired in post‐Fontan patients, PBPK and popPK simulations indicated that half of the rivaroxaban doses for the same body weight given to pediatric patients treated for acute VTE would yield in pediatric post‐Fontan patients exposures similar to the exposure observed in adult patients receiving 10 mg rivaroxaban once daily for thromboprophylaxis. Simulation‐derived doses (7.5 mg rivaroxaban once daily for body weights 30–<50 kg and 10 mg once daily for body weights ≥50 kg) were therefore included in the recent US label of rivaroxaban for thromboprophylaxis in children aged 2 years and older with congenital heart disease who have undergone the Fontan procedure.

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.

Population Pharmacokinetic Models for Direct Oral Anticoagulants: A Systematic Review and Clinical Appraisal Using Exposure Simulation

Available data have shown an association between direct oral anticoagulant (DOAC) plasma concentration and clinical, particularly bleeding, events. Factors that may influence DOAC plasma concentration are therefore the focus of particular attention. Population pharmacokinetic (PopPK) analyses can help in identifying such factors while providing predictive models. The main aim of the present study was to identify all the PopPK models to date for the four most frequently used DOACs (dabigatran, apixaban, rivaroxaban, and edoxaban). The secondary aim was to use these models to simulate different DOAC plasma concentration–time profiles in relevant clinical scenarios. The results of our model‐based simulations confirm the clinical relevance of the known major factors influencing DOAC exposure and support the current approved dose adaptation, at least for atrial fibrillation. They also highlight how the accumulation of covariates, not currently considered for dose adaptation due to their seemingly minor influence on DOAC exposure, lead to supratherapeutic blood concentrations and could thus enhance the risk of major bleeding. The present results therefore question DOAC dose adaptation in the presence of these covariates, such as drug–drug interaction or genotypes, alongside the known existing covariates. As the overall effect of accumulation of several covariates could be difficult to apprehend for the clinicians, PopPK modeling could represent an interesting approach for informed precision dosing and to improve personalized prescription of DOACs.

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.

Biopharmaceutics considerations for direct oral anticoagulants

Vitamin K antagonists (VKA) and direct oral anticoagulants (DOACs) have been clinically used in the treatment of coagulation disorders. There are four DOACs approved since 2010 (dabigatran etexilate, rivaroxaban, apixaban, and edoxaban), and they were designed to overcome the practical limitations of VKA. This review summarized biopharmaceutics considerations about DOACs, which are critically discussed, applying risk analyses to subside the further classification of these drugs according to the Biopharmaceutics Classification System (BCS). These discussions included data compiled about physicochemical properties, equilibrium solubility, permeability, and drug dissolution of DOACs. From the biopharmaceutics characteristics is possible to identify critical variables related to the absorption process, which can help in the design of new formulations. The data were compared with the criteria recommended by regulatory agencies for the biopharmaceutics classification according to the BCS. From that, these data may be used to discuss the approval of generic medicines by the BCS-based biowaiver, and the clinical risks arising from novel formulations with DOACs. However, although there are indications of biopharmaceutics classifications for DOACs, conclusive information to classify these compounds according to the BCS is lacking, requiring more experimental studies to achieve this aim. Conclusive information is essential for a safe decision about the biowaiver, as well as to guide the development of new formulations containing the DOACs.

Population Pharmacokinetics of Rivaroxaban in Chinese Patients with Non-Valvular Atrial Fibrillation: A Prospective Multicenter Study

BACKGROUND AND OBJECTIVE

Rivaroxaban is a novel oral anticoagulant widely used for thromboprophylaxis in patients with non-valvular atrial fibrillation (NVAF). The present study aimed to develop a population pharmacokinetic (PPK) model for rivaroxaban in Chinese patients with NVAF.

METHODS

We performed a prospective multicenter study. The plasma concentration of rivaroxaban was directly detected by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and indirectly by rivaroxaban-calibrated chromogenic anti-Xa assay (STA^®). Gene polymorphisms were detected by MassARRAY single nucleotide polymorphism genotyping technology. Nonlinear mixed-effects modeling was used to develop the PPK model for rivaroxaban in patients with NVAF, and we simulated the steady-state rivaroxaban exposures under different dosing strategies in different covariate levels.

RESULTS

A total of 150 patients from five centers were recruited, including 263 plasma concentrations detected by HPLC-MS/MS, 2626 gene polymorphisms, and 131 plasma concentrations detected by anti-Xa assay. In our study, an oral one-compartment model was used to describe the pharmacokinetics of rivaroxaban in patients with NVAF. In the final model, the estimated apparent clearance (CL/F) and volume of distribution (V/F) were 5.79 L/h (relative standard error [RSE] 4.4%) and 51.5 L (RSE 5.0%), respectively. Covariates in the final model included creatinine clearance, total bilirubin, rs4728709, and body weight. The simulation results showed that in the 15 mg once-daily dosing regimen, in most instances the maximum plasma concentration at steady state (C_max,ss) and trough plasma concentration at steady state (C_min,ss) were in the target range for different covariate levels. When patients were administered rivaroxaban 15 or 20 mg once daily, the C_max,ss and C_min,ss in the different bodyweight levels were also in the target range. For patients with the ABCB1 rs4728709 mutation, the C_min,ss in the 10, 15, and 20 mg once-daily dosing regimens were lower than the target range. The anti-Xa assay was highly linearly correlated with the HPLC-MS/MS method [y = 1.014x - 2.4648 (R² = 0.97)].

CONCLUSIONS

Our study was the first multicenter PPK model for rivaroxaban in Chinese patients with NVAF (Alfalfa-RIVAAF-PPK). The study found that 15 mg once daily may be suitable as the principal rivaroxaban dose for Chinese patients with NVAF. For patients with the rs4728709 mutation, it may be necessary to examine insufficient anticoagulation. We found that the rivaroxaban-calibrated chromogenic anti-Xa assay and HPLC-MS/MS method were highly linearly correlated. Prospective studies with larger sample sizes and real-world studies are needed for further verification.

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.

The impact of advanced age on anticoagulant therapy for acute venous thromboembolism

INTRODUCTION

Management of venous thromboembolic events (VTE) has been completely changed after the introduction of direct oral anticoagulants (DOAC). VTE is common in the geriatric population, but the management of DOACs remains complex because of the lack of specific data in this polymedicated fragile population.An exhaustive search of anticoagulants in the indication of VTE was performed on PubMed, including data from clinical trials, observational studies, real-world data, drug-drug interaction studies, as well as various guidelines from scientific societies.

AREAS COVERED

The present review aims to summarize our current knowledge on the era of DOACs in the management of VTE in the elderly. This involves learning the pharmacokinetics/pharmacodynamics of drugs specific to geriatrics, the problem of drug-drug interactions, and the main randomized clinical trials validating the use of DOACs.

EXPERT OPINION

DOACs have become an essential part of the management of VTE in the elderly, both for their efficacy and safety. However, we are faced with a list of unmet needs, such as the relevance of DOACs in the very elderly, cancer patients, and those with renal impairment. Clinicians and pharmacists must remain cautious about comedications, as well as about the patient's comorbidities.

Rivaroxaban Pharmacokinetics in Obese Subjects: A Systematic Review

INTRODUCTION

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality globally. The direct oral anticoagulants, including rivaroxaban, are relatively novel therapeutic options in the treatment and prevention of VTE. There is a conflicting and inconclusive evidence surrounding the pharmacokinetics (PK) of rivaroxaban in patients with VTE who are obese.

OBJECTIVES

We conducted a systematic review to provide an overview, and to synthesize the available evidence in the current literature pertaining to rivaroxaban PK in obese subjects who are healthy or diseased.

METHODS

The PubMed, Embase, ScienceDirect, Rayyan, and Cochrane Library databases were systematically searched from 1 May 2021 through 28 February 2022. Studies investigating rivaroxaban PK in adult obese subjects were included in the review. Pertinent data, including anthropometric parameters, rivaroxaban dosage regimen, PK parameters, PK model, and outcome measures were extracted. Reference values of rivaroxaban PK parameters in the general population were used for comparison purposes. The review protocol was registered in the PROSPERO database (CRD42020177770).

RESULTS

In the 11 studies included in this systematic review, over 7140 healthy or diseased subjects received rivaroxaban therapy, with varying clinical indications in the diseased population. The reported PK parameters of rivaroxaban in obese subjects compared with reference values in the general population were variable. The reported values of the volume of distribution (V_d) among obese subjects (73.4-82.8 L) fell within the range of values reported/calculated for the general population (59.4-104 L), assuming complete bioavailability. However, some of the reported values of clearance (CL) in obese subjects (7.86-16.8 L.h^-1) do not fall within the range of values reported/calculated for the general population (5.57-11.3 L.h^-1). The reported maximum plasma concentrations in obese subjects versus the general population following a 10 mg dose were 149 vs. 143-180 µg.L^-1, and following a 20 mg dose were 214-305 vs. 299-360 µg.L^-1, respectively. The area under the plasma concentration versus time curves (AUC) over different intervals in obese subjects versus the general population following a 10 mg dose were 1155 (AUC from time zero to infinity [AUC_∞]) vs. 1029 (AUC_∞) µg.h.L^-1; and 1204-2800 (AUC from time zero to 24 h [AUC₂₄]) vs. 3200 (AUC₂₄) µg.h.L^-1, respectively, following a 20 mg dose. The reported values of half-life and time to reach the maximum plasma concentration in obese subjects versus the general population were not consistent across studies.

CONCLUSION

Variable changes and inconsistencies in different rivaroxaban PK parameters were reported in obese subjects. Further well-designed studies are warranted to better characterize the PK and clinical outcomes of rivaroxaban in subjects with obesity.

Apixaban and rivaroxaban in obese patients treated for venous thromboembolism: Drug levels and clinical outcomes

BACKGROUND

Direct oral anticoagulants (DOAC) use remains challenging in obese patients treated for Venous-Thrombo-Embolism (VTE) due to the paucity of prospective and dedicated studies.

OBJECTIVE

To assess rivaroxaban and apixaban concentrations at different time-points after intake, in obese patients followed at a thrombosis center and treated for VTE; to define factors associated with DOAC levels outside the on-therapy ranges; and to evaluate bleeding and thrombosis rates during follow-up.

METHODS

Observational prospective study in two French University hospitals. Apixaban or rivaroxaban concentrations were measured after the first visit, regardless of last intake in obese patients receiving DOAC for VTE. Concentrations were compared to published reference values for non-obese patients. Demographic, clinical, biological and therapeutic data were collected. Univariate and multivariate analyses were performed to identify factors associated to DOAC concentrations outside the on-therapy ranges.

RESULTS

Out of the 146 patients included, 22 (15%) had DOAC concentrations outside the on-therapy ranges, mainly in the rivaroxaban group (n = 17). Age ≤ 63 years, use of rivaroxaban and time since last intake ≤8 h were associated with DOAC concentrations outside the on-therapy ranges, in multivariable analysis. During the median follow-up of 16 months, two (1%) patients receiving apixaban had recurrent VTE. No patient had major bleeding, 11 (8%) patients had minor bleeding.

CONCLUSION

In this specific prospective bi-centric study dedicated to VTE obese patients, use of DOACs at fixed doses led to concentrations similar to those of non-obese patients in a high proportion of patients, without any effect of the BMI, and with risk-benefit profile comparable to non-obese patients.

Direct Oral Anticoagulants in Patients with Obesity and Atrial Fibrillation: Position Paper of Italian National Association of Hospital Cardiologists (ANMCO)

The use of the direct oral anticoagulants dabigatran, rivaroxaban, apixaban and edoxaban (DOACs) offers some major advantages over warfarin and other vitamin K antagonists (VKAs). One advantage is the possibility to use a fixed dose in normal-weight patients, overweight patients and patients with obesity. However, the "one size fits all" strategy raised a concern regarding the possibility to undertreat patients with a high body mass index. No randomized controlled trials (RCTs) have ever compared VKAs and DOACs in this population. We analyzed data from the literature on DOAC pharmacokinetics and pharmacodynamics, results from the four pivotal phase III trials on non-valvular atrial fibrillation, retrospective observational studies and metanalyses. While we are aware of the limitation imposed by the absence of specific RCTs, we propose the position of the Italian Association of Hospital Cardiologists (ANMCO) on the use of DOACs in patients with obesity based on the existing evidence.

Dosing Regimen Prediction and Confirmation with Rivaroxaban for Thromboprophylaxis in Children after the Fontan Procedure: Insights from the Phase III UNIVERSE Study

Thrombosis remains an important complication for children with single ventricle physiology post-Fontan procedure and effective thromboprophylaxis is an important unmet medical need. To obviate conventional dose-finding studies and expedite clinical development, a rivaroxaban dose regimen for this indication was determined utilizing a model-informed drug development approach. A physiologically based pharmacokinetic (PBPK) rivaroxaban model was used to predict a pediatric dosing regimen that would produce drug exposures similar to that of 10 mg once daily in adults. This regimen was used in an open-label, multicenter Phase 3 study, which investigated the use of rivaroxaban for thromboprophylaxis in post-Fontan patients 2 to 8 years of age. The pharmacokinetics (PK) of rivaroxaban was assessed in Part A (n = 12) and in Part B (n = 64) of UNIVERSE. The safety and efficacy in the rivaroxaban group were compared to those in the acetylsalicylic acid group for 12 months. Pharmacodynamic endpoints were assessed in both parts of the study. Rivaroxaban exposures achieved in Part A and B were similar to the adult reference exposures. Prothrombin time also showed similarity to the adult reference. Exposure-response analysis did not identify a quantitative relationship between rivaroxaban exposures and efficacy/safety outcomes within the observed exposure ranges. A body-weight based dose regimen selected by PBPK modeling was shown in the UNIVERSE study to be appropriate for thromboprophylaxis in the post-Fontan pediatric population. Model-based dose selection can support pediatric drug development and bridge adult dose data to pediatrics, thereby obviating the need for dose-finding studies in pediatric programs. This article is protected by copyright. All rights reserved.

Use of direct oral anticoagulants in patients with obesity for treatment and prevention of venous thromboembolism: Updated communication from the ISTH SSC Subcommittee on Control of Anticoagulation

Although direct-acting oral anticoagulants (DOACs) have widespread first-line use for treatment and prevention of venous thromboembolism (VTE), uncertainty remains regarding their efficacy and safety in patients with obesity. We reviewed available data for use of DOACs for VTE treatment and prevention in patients with obesity, including phase 3, phase 4, meta-analyses, and pharmacokinetic and pharmacodynamics studies. In addition, we reviewed available data regarding DOACs in bariatric surgery. We provide updated guidance recommendations on using DOACs in patients with obesity for treatment and prevention of VTE, as well as following bariatric surgery.

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.

Comparative Effectiveness and Safety of Rivaroxaban and Warfarin Among Nonvalvular Atrial Fibrillation (NVAF) Patients with Obesity and Polypharmacy in the United States (US)

Introduction

Current evidence indicates that rivaroxaban may be a safe and effective alternative to warfarin among patients with nonvalvular atrial fibrillation (NVAF) and obesity. However, evidence regarding the impact of polypharmacy is limited in this population. The present study evaluated the effectiveness and safety of rivaroxaban versus warfarin among NVAF patients with obesity and polypharmacy in the US.

Methods

De-identified health insurance claims data from the IQVIA PharMetrics^® Plus data (01/2010–09/2019) were used to identify NVAF patients with obesity (BMI ≥ 30 kg/m²) and polypharmacy (≥ 5 medications) initiated on rivaroxaban or warfarin. Inverse probability of treatment weighting (IPTW) was used to adjust for imbalances between groups. Study outcomes were evaluated up to 36 months post-treatment initiation and included the composite of stroke or systemic embolism (stroke/SE) and major bleeding. Subgroup analyses were conducted stratified by polypharmacy category (5–9 or ≥ 10 medications). Outcomes were assessed using Cox proportional hazards regression models with hazard ratios (HR) and 95% confidence intervals (CIs).

Results

A total of 7000 and 3920 NVAF patients with obesity and polypharmacy were initiated on rivaroxaban and warfarin, respectively. At 36 months of follow-up, rivaroxaban was associated with a 29% lower risk of stroke/SE relative to warfarin (HR 0.71, 95% CI 0.57, 0.90). Major bleeding risk was not significantly different among rivaroxaban- compared to warfarin-treated patients (HR 0.85, 95% CI 0.70, 1.03). Subgroup analyses yielded results that were largely consistent with the overall polypharmacy analysis.

Conclusions

These results suggest that rivaroxaban is an effective and safe treatment option among NVAF patients with obesity and polypharmacy in a commercially-insured US population.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12325-021-01746-2.

Associations between model-predicted rivaroxaban exposure and patient characteristics and efficacy and safety outcomes in the prevention of venous thromboembolism

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

Associations between model-predicted rivaroxaban exposure and patient characteristics and efficacy and safety outcomes in the treatment of venous thromboembolism

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

Associations between model-predicted rivaroxaban exposure and patient characteristics and efficacy and safety outcomes in patients with non-valvular atrial fibrillation

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

Post-Discharge Prophylaxis With Rivaroxaban Reduces Fatal and Major Thromboembolic Events in Medically Ill Patients

Background

Hospitalized acutely ill medical patients are at risk for fatal and major thromboembolic events. Whether use of extended-duration primary thromboprophylaxis can prevent such events is unknown.

Objectives

The purpose of this study was to evaluate whether extended-duration rivaroxaban reduces the risk of venous and arterial fatal and major thromboembolic events without significantly increasing major bleeding in acutely ill medical patients after discharge.

Methods

MARINER (A Study of Rivaroxaban [JNJ-39039039] on the Venous Thromboembolic Risk in Post-Hospital Discharge Patients) studied acutely ill medical patients with additional risk factors for venous thromboembolism (VTE). Medically ill patients with a baseline creatinine clearance ≥50 ml/min were randomized in a double-blind fashion to rivaroxaban 10 mg or placebo daily at hospital discharge for 45 days. Exploratory efficacy analyses were performed with the intent-to-treat population including all data through day 45. Time-to-event curves were calculated using the Kaplan-Meier method. A blinded independent committee adjudicated all clinical events.

Results

In total, 4,909 patients were assigned to rivaroxaban and 4,913 patients to placebo. The mean age was 67.8 years, 55.5% were men, mean baseline creatinine clearance was 87.8 ml/min, and mean duration of hospitalization was 6.7 days. The pre-specified composite efficacy endpoint (symptomatic VTE, myocardial infarction, nonhemorrhagic stroke, and cardiovascular death) occurred in 1.28% and 1.77% of patients in the rivaroxaban and placebo groups, respectively (hazard ratio: 0.72; 95% confidence interval: 0.52 to 1.00; p = 0.049), whereas major bleeding occurred in 0.27% and 0.18% of patients in the rivaroxaban and placebo groups, respectively (hazard ratio: 1.44; 95% confidence interval: 0.62 to 3.37; p = 0.398).

Conclusions

Extended-duration rivaroxaban in hospitalized medically ill patients resulted in a 28% reduction in fatal and major thromboembolic events without a significant increase in major bleeding. (A Study of Rivaroxaban [JNJ-39039039] on the Venous Thromboembolic Risk in Post-Hospital Discharge Patients [MARINER]; NCT02111564)

Healthcare resource utilization and costs of rivaroxaban versus warfarin among non-valvular atrial fibrillation (NVAF) patients with obesity in a US population

AIM

To assess the real-world healthcare resource utilization (HRU) and costs of patients with non-valvular atrial fibrillation (NVAF) and obesity newly initiated on rivaroxaban or warfarin in the US.

METHODS

This retrospective study used IQVIA PharMetrics Plus data (01/2010-09/2019) to evaluate patients (≥18 years) with NVAF and obesity (body mass index ≥30 kg/m²) initiated on rivaroxaban or warfarin (on or after 01/2013). Inverse probability of treatment weighting (IPTW) was used to adjust for confounding between cohorts. HRU and costs were assessed post-treatment initiation. Weighted cohorts were compared using Poisson regression models and cost differences, with 95% confidence intervals (CIs) and p values generated using non-parametric bootstrap procedures.

RESULTS

After IPTW, 10,555 and 5,080 patients were initiated on rivaroxaban and warfarin, respectively (mean age: 59 years). At 12 months follow-up, the rivaroxaban cohort had lower all-cause HRU, including fewer hospitalizations (rate ratio [RR]: 0.80, 95% CI: 0.74, 0.87), emergency room visits (RR: 0.89, 95% CI: 0.83, 0.97), and outpatient visits (RR: 0.72, 95% CI: 0.69, 0.77; all p < .05). Medical costs were also reduced in the rivaroxaban cohort (mean difference: -$6,759, 95% CI: -$9,814, -$3,311) due to reduced hospitalization costs (mean difference: -$5,967, 95% CI: -$8,721, -$3,327), resulting in lower total all-cause healthcare costs compared to the warfarin cohort (mean difference: -$4,579, 95% CI: -$7,609, -$1,052; all p < .05). The rivaroxaban cohort also had lower NVAF-related HRU and medical costs driven by lower hospitalization at 12 months post-treatment initiation. HRU and cost reductions associated with rivaroxaban persisted up to 36 months of follow-up.

LIMITATIONS

Claims data may have contained inaccuracies and obesity was classified based on ICD diagnosis codes given that patient BMI values were not available.

CONCLUSIONS

Rivaroxaban was associated with reduced HRU and costs compared to warfarin among NVAF patients with obesity in a real-world US setting.

Dose Optimization in Kidney Disease: Opportunities for PBPK Modeling and Simulation

Kidney disease affects pharmacokinetic (PK) profiles of not only renally cleared drugs but also nonrenally cleared drugs. The impact of kidney disease on drug disposition has not been fully elucidated, but describing the extent of such impact is essential for conducting dose optimization in kidney disease. Accurate evaluation of kidney function has been a clinical interest for dose optimization, and more scientists pay attention and conduct research for clarifying the role of drug transporters, metabolic enzymes, and their interplay in drug disposition as kidney disease progresses. Physiologically based pharmacokinetic (PBPK) modeling and simulation can provide valuable insights for dose optimization in kidney disease. It is a powerful tool to integrate discrete knowledge from preclinical and clinical research and mechanistically investigate system- and drug-dependent factors that may contribute to the changes in PK profiles. PBPK-based prediction of drug exposures may be used a priori to adjust dosing regimens and thereby minimize the likelihood of drug-related toxicity. With real-time clinical studies, parameter estimation may be performed with PBPK approaches that can facilitate identification of sources of interindividual variability. PBPK modeling may also facilitate biomarker research that aids dose optimization in kidney disease. U.S. Food and Drug Administration guidances related to conduction of PK studies in kidney impairment and PBPK documentation provide the foundation for facilitating model-based dose-finding research in kidney disease.

Fixed dose rivaroxaban can be used in extremes of bodyweight: A population pharmacokinetic analysis

BACKGROUND

Emerging safety and efficacy data for rivaroxaban suggest traditional therapy and rivaroxaban are comparable in the morbidly obese. However, real-world data that indicate pharmacokinetic (PK) parameters are comparable at the extremes of body size are lacking. The International Society of Thrombosis and Haemostasis Scientific and Standardisation Committee (ISTH SSC) suggests avoiding the use of direct oral anticoagulants (DOACs) in patients weighing >120 kg or with a body mass index >40 kg/m2 and gives no recommendation on the use of DOACs in those <50 kg.

OBJECTIVES

To generate a population PK model to understand the influence of bodyweight on rivaroxaban exposure from clinical practice data.

METHOD

Rivaroxaban plasma concentrations and patient characteristics were collated between 2013 and 2018 at King's College Hospital anticoagulation clinic. A population PK model was developed using a nonlinear mixed effects approach and then used to simulate rivaroxaban concentrations at the extremes of bodyweight.

RESULTS

A robust population PK model derived from 913 patients weighing between 39 kg and 172 kg was developed. The model included data from n = 86 >120 kg, n = 74 BMI >40 kg/m2 , and n = 30 <50 kg. A one-compartment model with between-subject variability on clearance and a proportional error model best described the data. Creatinine clearance calculated by Cockcroft-Gault, with lean bodyweight as the weight descriptor in this equation, was the most significant covariate influencing rivaroxaban exposure.

CONCLUSIONS

Our work demonstrates rivaroxaban can be used at extremes of bodyweight provided renal function is satisfactory. We recommend that the ISTH SSC revises the current guidance with respect to rivaroxaban at extremes of body size.

Rivaroxaban for treatment of pediatric venous thromboembolism. An Einstein-Jr phase 3 dose-exposure-response evaluation

BACKGROUND

Recently, the randomized EINSTEIN-Jr study showed similar efficacy and safety for rivaroxaban and standard anticoagulation for treatment of pediatric venous thromboembolism (VTE). The rivaroxaban dosing strategy was established based on phase 1 and 2 data in children and through pharmacokinetic (PK) modeling.

METHODS

Rivaroxaban treatment with tablets or the newly developed granules-for-oral suspension formulation was bodyweight-adjusted and administered once-daily, twice-daily, or thrice-daily for children with bodyweights of ≥30, ≥12 to <30, and <12 kg, respectively. Previously, these regimens were confirmed for children weighing ≥20 kg but only predicted in those <20 kg. Based on sparse blood sampling, the daily area under the plasma concentration-time curve [AUC(0-24)ss ] and trough [Ctrough,ss ] and maximum [Cmax,ss ] steady-state plasma concentrations were derived using population PK modeling. Exposure-response graphs were generated to evaluate the potential relationship of individual PK parameters with recurrent VTE, repeat imaging outcomes, and bleeding or adverse events. A taste-and-texture questionnaire was collected for suspension-recipients.

RESULTS

Of the 335 children (aged 0-17 years) allocated to rivaroxaban, 316 (94.3%) were evaluable for PK analyses. Rivaroxaban exposures were within the adult exposure range. No clustering was observed for any of the PK parameters with efficacy, bleeding, or adverse event outcomes. Results were similar for the tablet and suspension formulation. Acceptability and palatability of the suspension were favorable.

DISCUSSION

Based on this analysis and the recently documented similar efficacy and safety of rivaroxaban compared with standard anticoagulation, we conclude that bodyweight-adjusted pediatric rivaroxaban regimens with either tablets or suspension are validated and provide for appropriate treatment of children with VTE.

Rivaroxaban Precision Dosing Strategy for Real-World Atrial Fibrillation Patients

Rivaroxaban is a direct-acting oral anticoagulant approved to prevent strokes in patients with atrial fibrillation. Dosage recommendations are approved for all adult patients to receive either 15 mg or 20 mg once daily depending upon renal function. There are a number of reasons to believe rivaroxaban dosing could be more effective and/or safer for more patients if increased dosing precision is available. Because real-world patients are more diverse than those studied in phase III clinical trials, we evaluated the extremes of creatinine clearance (CrCl) on rivaroxaban clearance using a published population pharmacokinetic model and applying exposure variation limits (±20%) based on published literature. The proposed dosing recommendations are 10 mg once daily (CrCl 15-29 ml/min), 15 mg once daily (CrCl 30-69 ml/min), 10 mg twice daily (CrCl 70-159 ml/min), and 15 mg twice daily (CrCl 160-250 ml/min). These new dosing recommendations should be prospectively tested for predictive accuracy and to assess the impact on AF patient efficacy and safety.

Optimal Rivaroxaban Dose in Asian Patients With Atrial Fibrillation and Normal or Mildly Impaired Renal Function

Background and Purpose- Although rivaroxaban 15 mg (R15) was only given to patients with creatinine clearance (CrCl) ≤50 mL/min in the pivotal clinical trial, this dose has been commonly prescribed in Asian patients with nonvalvular atrial fibrillation regardless of renal function. There is a paucity of information on the clinical outcomes of R15 compared with rivaroxaban 20 mg (R20) in patients with CrCl ≥50 mL/min. This study aimed to examine the effectiveness and safety of 2 doses of rivaroxaban in Asian patients with atrial fibrillation and CrCl ≥50 mL/min. Methods- Using the Korean National Health Insurance Service database, patients with atrial fibrillation and normal or mildly impaired renal function (CrCl ≥50 mL/min) and naive to rivaroxaban or warfarin were included from January 2014 to December 2016. Three separate 1:1 propensity score-matched cohorts were conducted: R20 versus warfarin (n=15 584), R15 versus warfarin (n=11 554), and R20 versus R15 (n=10 392). Hazard ratios for ischemic stroke, intracranial hemorrhage, gastrointestinal bleeding, major bleeding, all-cause death, and composite clinical outcome were analyzed. Results- Compared with warfarin, both R20 and R15 showed significantly lower risk for ischemic stroke, major bleeding (mainly through reduction of intracranial hemorrhage), and all-cause death. Compared with R15, R20 showed better results for the composite clinical outcome (hazard ratio, 0.852; 95% CI, 0.735-0.988). This benefit was consistently observed in patients aged ≥80 years and those <50 kg. R20 was associated with higher risk of major bleeding than R15 in patients with marginal CrCl (50-60 mL/min). Conclusions- Among Asians with atrial fibrillation and CrCl ≥50 mL/min, both R20 and R15 were associated with reduced risk of ischemic stroke, intracranial hemorrhage, major bleeding, and all-cause death without significantly increased risk of gastrointestinal bleeding compared with warfarin. In patients with CrCl ≥50 mL/min, on-label R20 showed better results for the composite clinical outcome compared with off-label R15.

Rivaroxaban compared with standard anticoagulants for the treatment of acute venous thromboembolism in children: a randomised, controlled, phase 3 trial

BACKGROUND

Treatment of venous thromboembolism in children is based on data obtained in adults with little direct documentation of its efficacy and safety in children. The aim of our study was to compare the efficacy and safety of rivaroxaban versus standard anticoagulants in children with venous thromboembolism.

METHODS

In a multicentre, parallel-group, open-label, randomised study, children (aged 0-17 years) attending 107 paediatric hospitals in 28 countries with documented acute venous thromboembolism who had started heparinisation were assigned (2:1) to bodyweight-adjusted rivaroxaban (tablets or suspension) in a 20-mg equivalent dose or standard anticoagulants (heparin or switched to vitamin K antagonist). Randomisation was stratified by age and venous thromboembolism site. The main treatment period was 3 months (1 month in children <2 years of age with catheter-related venous thromboembolism). The primary efficacy outcome, symptomatic recurrent venous thromboembolism (assessed by intention-to-treat), and the principal safety outcome, major or clinically relevant non-major bleeding (assessed in participants who received ≥1 dose), were centrally assessed by investigators who were unaware of treatment assignment. Repeat imaging was obtained at the end of the main treatment period and compared with baseline imaging tests. This trial is registered with ClinicalTrials.gov, number NCT02234843 and has been completed.

FINDINGS

From Nov 14, 2014, to Sept 28, 2018, 500 (96%) of the 520 children screened for eligibility were enrolled. After a median follow-up of 91 days (IQR 87-95) in children who had a study treatment period of 3 months (n=463) and 31 days (IQR 29-35) in children who had a study treatment period of 1 month (n=37), symptomatic recurrent venous thromboembolism occurred in four (1%) of 335 children receiving rivaroxaban and five (3%) of 165 receiving standard anticoagulants (hazard ratio [HR] 0·40, 95% CI 0·11-1·41). Repeat imaging showed an improved effect of rivaroxaban on thrombotic burden as compared with standard anticoagulants (p=0·012). Major or clinically relevant non-major bleeding in participants who received ≥1 dose occurred in ten (3%) of 329 children (all non-major) receiving rivaroxaban and in three (2%) of 162 children (two major and one non-major) receiving standard anticoagulants (HR 1·58, 95% CI 0·51-6·27). Absolute and relative efficacy and safety estimates of rivaroxaban versus standard anticoagulation estimates were similar to those in rivaroxaban studies in adults. There were no treatment-related deaths.

INTERPRETATION

In children with acute venous thromboembolism, treatment with rivaroxaban resulted in a similarly low recurrence risk and reduced thrombotic burden without increased bleeding, as compared with standard anticoagulants.

FUNDING

Bayer AG and Janssen Research & Development.

Bodyweight-adjusted rivaroxaban for children with venous thromboembolism (EINSTEIN-Jr): results from three multicentre, single-arm, phase 2 studies

BACKGROUND

Rivaroxaban has been shown to be efficacious for treatment of venous thromboembolism in adults, and has a reduced risk of bleeding compared with standard anticoagulants. We aimed to develop paediatric rivaroxaban regimens for the treatment of venous thromboembolism in children and adolescents.

METHODS

In this phase 2 programme, we did three studies to evaluate rivaroxaban treatment in children younger than 6 months, aged 6 months to 5 years, and aged 6-17 years. Our studies used a multicentre, single-arm design at 54 sites in Australia, Europe, Israel, Japan, and north America. We included children with objectively confirmed venous thromboembolism previously treated with low-molecular weight heparin, fondaparinux, or a vitamin K antagonist for at least 2 months or, in children who had catheter-related venous thromboembolism for at least 6 weeks. We administered rivaroxaban orally in a bodyweight-adjusted 20 mg-equivalent dose, based on physiologically-based pharmacokinetic modelling predictions and EINSTEIN-Jr phase 1 data in young adults, in either a once-daily (tablets; for those aged 6-17 years), twice-daily (in suspension; for those aged 6 months to 11 years), or three times-daily (in suspension; for those younger than 6 months) dosing regimen for 30 days (or 7 days for those younger than 6 months). The primary aim was to define rivaroxaban treatment regimens that match the target adult exposure range. The principal safety outcome was major bleeding and clinically relevant non-major bleeding. Analyses were per-protocol. The predefined efficacy outcomes were symptomatic recurrent venous thromboembolism, asymptomatic deterioration on repeat imaging at the end of the study treatment period. These trials are registered at ClinicalTrials.gov, numbers NCT02564718, NCT02309411, and NCT02234843.

FINDINGS

Between Feb 11, 2013, and Dec 20, 2017, we enrolled 93 children (ten children younger than 6 months; 15 children aged 6 months to 1 year; 25 children aged 2-5 years; 32 children aged 6-11 years; and 11 children aged 12-17 years) into our study. 89 (96%) children completed study treatment (30 days of treatment, or 7 days in those younger than 6 months), and 93 (100%) children received at least one dose of study treatment and were evaluable for the primary endpoints. None of the children had a major bleed, and four (4%, 95% CI 1·2-10·6) of these children had a clinically relevant non-major bleed (three children aged 12-17 years with menorrhagia and one child aged 6-11 years with gingival bleeding). We found no symptomatic recurrent venous thromboembolism in any patients (0%, 0·0-3·9). 24 (32%) of 75 patients with repeat imaging had their thrombotic burden resolved, 43 (57%) patients improved, and eight (11%) patients were unchanged. No patient deteriorated. We confirmed therapeutic rivaroxaban exposures with once-daily dosing in children with bodyweights of at least 30 kg and with twice-daily dosing in children with bodyweights of at least 20 kg and less than 30 kg. Children with low bodyweights (<20 kg, particularly <12 kg) showed low exposures so, for future studies, rivaroxaban dosages were revised for these weight categories, to match the target adult exposure range. 61 (66%) of 93 children had adverse events during the study. Pyrexia was the most common adverse event (ten [11%] events), and anaemia and neutropenia or febrile neutropenia were the most frequent grade 3 or worse events (four [4%] events each). No children died or were discontinued from rivaroxaban because of adverse events.

INTERPRETATION

Treatment with bodyweight-adjusted rivaroxaban appears to be safe in children. The treatment regimens that we confirmed in children with bodyweights of at least 20 kg and the revised treatment regimens that we predicted in those with bodyweights less than 20 kg will be evaluated in the EINSTEIN-Jr phase 3 trial in children with acute venous thromboembolism.

FUNDING

Bayer AG, Janssen Research and Development.

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.