Population pharmacokinetics and pharmacodynamics of rivaroxaban in patients with acute coronary syndromes

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.

Population Pharmacokinetics and Probability of Target Attainment Analysis of Nadroparin in Different Stages of COVID-19

BACKGROUND AND OBJECTIVE

The risk of thrombotic complications in critical patients with COVID-19 remains extremely high, and multicenter trials failed to prove a survival benefit of escalated doses of low-molecular-weight heparins (nadroparin calcium) in this group. The aim of this study was to develop a pharmacokinetic model of nadroparin according to different stages of COVID-19 severity.

METHODS

Blood samples were obtained from 43 patients with COVID-19 who received nadroparin and were treated with conventional oxygen therapy, mechanical ventilation, and extracorporeal membrane oxygenation. We recorded clinical, biochemical, and hemodynamic variables during 72 h of treatment. The analyzed data comprised 782 serum nadroparin concentrations and 219 anti-Xa levels. We conducted population nonlinear mixed-effects modeling (NONMEM) and performed Monte Carlo simulations of the probability of target attainment for reaching 0.2-0.5 IU/mL anti-Xa levels in study groups.

RESULTS

We successfully developed a one-compartment model to describe the population pharmacokinetics of nadroparin in different stages of COVID-19. The absorption rate constant of nadroparin was 3.8 and 3.2 times lower, concentration clearance was 2.22 and 2.93 times higher, and anti-Xa clearance was 0.87 and 1.1 times higher in mechanically ventilated patients and the extracorporeal membrane oxygenation group compared with patients treated with conventional oxygen, respectively. The newly developed model indicated that 5.900 IU of nadroparin given subcutaneously twice daily in the mechanically ventilated patients led to a similar probability of target attainment of 90% as 5.900 IU of subcutaneous nadroparin given once daily in the group supplemented with conventional oxygen.

CONCLUSIONS

Different nadroparin dosing is required for patients undergoing mechanical ventilation and extracorporeal membrane oxygenation to achieve the same targets as those for non-critically ill patients.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier no. NCT05621915.

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.

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.

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

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

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

OBJECTIVE

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

DESIGN

Descriptive retrospective study.

SETTING

Two veterinary teaching hospitals.

ANIMALS

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

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

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

CONCLUSIONS

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

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.

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.

The Pharmacology, Efficacy, and Safety of Rivaroxaban in Obese Patient Populations

Cardiovascular disease (CVD) remains the leading cause of death in the USA. Several risk factors have been identified, and obesity has become one of prominent concern. Excessive weight is considered a risk factor for CVD based on evidence linking it to a hypercoagulable state. Considering the prevalence of CVD and obesity in the USA, along with the increased risk for thrombus-related events, anticoagulation plays a significant role in prevention and treatment. Direct oral anticoagulants have taken the place of many traditional anticoagulants. Considering the recently approved indications and continued postmarketing studies conducted with rivaroxaban, this updated review provides data on the overall impact of obesity on this compound. This includes data obtained from both healthy obese volunteers and obese patients with various CVD conditions enrolled in rivaroxaban clinical trials, along with data obtained from postmarketing real-world evidence studies. Assessment of the clinical pharmacology and population pharmacokinetics in obese individuals revealed no clinically relevant effects of increased weight. Additionally, subgroup analyses from each of the pivotal phase III trials supporting the current approved labeling also demonstrated consistent efficacy and safety results in obese patients. Lastly, these findings are further supported by several recent real-world evidence studies assessing the continued effectiveness and safety of rivaroxaban. In conclusion, rivaroxaban’s overall pharmacological and clinical profile remained consistent in obese adults when assessed in both drug development and postmarketing studies, supporting the premise that higher weight does not necessitate adjustment in either dose strength or regimen.

The Pharmacology, Efficacy, and Safety of Rivaroxaban in Renally Impaired Patient Populations

Rivaroxaban is a factor Xa inhibitor oral anticoagulant first approved for use in the United States in 2011. Under the drug class commonly termed direct oral anticoagulants, rivaroxaban is approved for the most indications within its class, 7 indications, which are: (1) reduction of risk of stroke and systemic embolism (SE) in nonvalvular atrial fibrillation, (2) treatment of deep vein thrombosis (DVT), (3) treatment of pulmonary embolism (PE), (4) reduction in the risk of recurrence of DVT and/or PE, (5) prophylaxis of DVT following hip or knee replacement surgery, (6) prophylaxis of venous thromboembolism in acutely ill medical patients at risk for thromboembolic complications not at high risk of bleeding, and (7) reduction of risk of major cardiovascular events in patients with chronic coronary artery disease or peripheral artery disease. Considering the relationship between cardiovascular disease, renal impairment, and the use of oral anticoagulants, the following targeted review was created. This review reports the results of the primary pharmacology, pharmacokinetic modeling, clinical safety and efficacy, and real-world postmarketing effectiveness and safety of rivaroxaban in patients with various degrees of renal impairment. Based on these data, rivaroxaban is a viable option for when anticoagulation is needed in patients who have both cardiovascular disease and renal impairment. However, as with any therapy, the benefits and risks of intervention should be carefully assessed and balanced. Patients treated with rivaroxaban for several of its approved indications should have their kidney function assessed prior to and during continued therapy to ensure consistency with the drug label.

Impact of gene polymorphisms in drug-metabolizing enzymes and transporters on trough concentrations of rivaroxaban in patients with atrial fibrillation

Rivaroxaban is excreted from the body via multiple pathways involving glomerular filtration, drug-metabolizing enzymes and transporters. In this study, we aimed to examine the impact of single nucleotide polymorphisms in P-glycoprotein, breast cancer resistance protein, cytochrome P450 (CYP) 3A5 and CYP2J2 on the pharmacokinetics of rivaroxaban. Eighty-six patients with non-valvular atrial fibrillation (NVAF) undergoing AF catheter ablation were enrolled in this study. In these analyses, the dose-adjusted plasma trough concentration ratio (C_0h /D) of rivaroxaban was used as the pharmacokinetic index. The median (quartile range) rivaroxaban C_0h /D was 3.39 (2.08-5.21) ng/mL/mg (coefficient of variation: 80.5%). The C_0h /D did not differ significantly among ABCB1 c.3435C>T, c.2677G>A/T, c.1236C>T, ABCG2 c.421C>A, CYP3A5*3 and CYP2J2*7 genotypes. Stepwise selection multiple linear regression analysis showed that the estimated glomerular filtration rate was the only independent factor influencing the C_0h /D of rivaroxaban (R²  = 0.152, P < 0.001). There was a significant correlation between the C_0h of rivaroxaban and prothrombin time (PT) (rho = 0.357, P = 0.001). In patients with NVAF, pharmacokinetic genotype tests are unlikely to be useful for prediction of the C_0h of rivaroxaban.

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

Background

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

Methods

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

Results

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

Conclusions

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

Rivaroxaban and Aspirin in Peripheral Vascular Disease: a Review of Implementation Strategies and Management of Common Clinical Scenarios

PURPOSE OF REVIEW

Peripheral artery disease (PAD) affects an estimated 200 million people worldwide and is associated with significant cardiovascular morbidity and mortality. Cardiovascular risk is further increased among individuals with polyvascular disease, where either cerebrovascular or coronary artery disease is present in addition to PAD. In this review, we present common clinical scenarios encountered when managing patients with PAD and provide an evidence-based approach to prescribing optimal antithrombotics in this population.

RECENT FINDINGS

The COMPASS trial recently demonstrated that rivaroxaban 2.5 mg BID + ASA daily significantly reduces major adverse cardiac and limb events in patients with PAD. Despite these advances, morbidity following MALE events remains high. With widespread approval by federal health regulators, the COMPASS regimen should be strongly considered in PAD patients who do not have a high bleeding risk. Implementing the COMPASS regimen in patients with PAD, along with other vascular risk reduction strategies, will have a substantial impact on reducing atherothromboembolic risk in patients with established vascular disease.

Enhancing the Quality of Rivaroxaban Exposure Estimates Using Prothrombin Time in the Absence of Pharmacokinetic Sampling

Prothrombin time (PT) is a measure of coagulation status and was assessed in the majority of patients in the rivaroxaban phase II and III clinical trials as a pharmacodynamic marker. In the absence of sufficient phase III pharmacokinetic (PK) data to provide individual exposure measures for input into rivaroxaban exposure–response analyses, the aim of the present study was to investigate the use of PT‐adjustment approaches (i.e., the use of observed individual PT measurements) to enhance the prediction of individual rivaroxaban exposure metrics (derived using a previously developed integrated population PK model) based on the observed linear relationship between PT and rivaroxaban plasma concentrations. The PT‐adjustment approaches were established using time‐matched PK and PT measurements, which were available from 1,779 patients across four phase II trials and one phase III trial of rivaroxaban. PT‐adjusted exposure estimates improved the identification of statistically significant effects when compared with covariate‐only exposure estimates.

Effects of Verapamil and Diltiazem on the Pharmacokinetics and Pharmacodynamics of Rivaroxaban

Concomitant use of rivaroxaban with non-dihydropyridine calcium channel blockers (non-DHPs) might lead to an increase of systemic rivaroxaban exposure and anticoagulant effects in relation to the inhibition of metabolic enzymes and/or transporters by non-DHPs. This study was designed to evaluate the effects of verapamil and diltiazem on the pharmacokinetics and the prolongation of prothrombin time of rivaroxaban in rats. The data were analyzed using a pharmacokinetic/pharmacodynamics (PK/PD) modeling approach to quantify the influence of verapamil. Verapamil increased the systemic exposure of rivaroxaban by 2.8-fold (p <0.001) which was probably due to the inhibition of efflux transportation rather than metabolism. Prothrombin time was also prolonged in a proportional manner; diltiazem did not show any significant effects, however. A transit PK model in the absorption process comprehensively describes the double-peaks of rivaroxaban plasma concentrations and the corresponding change of prothrombin time with a simple linear relationship. The slope of prothrombin time vs. rivaroxaban plasma concentration in rats was retrospectively found to be insensitive by about 5.4-fold compared to than in humans. More than a 67% dose reduction in rivaroxaban is suggested in terms of both a pharmacokinetic point of view, and the sensitivity differences on the prolongation of prothrombin time when used concomitantly with verapamil.

Downregulation of ABCB1 gene in patients with total hip or knee arthroplasty influences pharmacokinetics of rivaroxaban: a population pharmacokinetic-pharmacodynamic study

PURPOSE

Rivaroxaban is a substrate for ABCB1 transporter and is commonly used in patients undergoing hip or knee replacement surgery for thromboprophylaxis. The objective of this study was to develop a population pharmacokinetic-pharmacodynamic (PK-PD) model to investigate the influence of ABCB1 gene expression and polymorphism on rivaroxaban exposure and anticoagulation effects.

METHODS

Five blood samples per patient were collected during 5 days after the surgery for the determination of rivaroxaban concentration in plasma and for determination of prothrombin time and partial thromboplastin time. Non-linear mixed effects model was used for a population PK-PD analysis and for testing covariate effects.

RESULTS

A one-compartment PK model with first-order absorption adequately described the pharmacokinetic data. The typical oral clearance (CL/F) was 6.12 L/h (relative standard error, 15.8%) and was associated with ABCB1 expression. Compared to base line before the surgery, a significant ABCB1 downregulation was observed 5 days after the surgery (p < 0.001). Prothrombin time and partial thromboplastin time were both linearly associated to the logarithm of the rivaroxaban plasma concentration.

CONCLUSIONS

We confirmed that variable rivaroxaban CL/F is associated with ABCB1 expression, which is in accordance with previous studies on P-glycoprotein involvement in rivaroxaban PK. Furthermore, we observed the downregulation of ABCB1 expression after the surgery. The cause remains unclear and further research is needed to explain the underlying mechanisms.

Influence of age on the pharmacokinetics, pharmacodynamics, efficacy, and safety of rivaroxaban

OBJECTIVE

Atrial fibrillation, peripheral and coronary artery disease, and venous thromboembolism are major risk factors for stroke, disability, and death in the rapidly growing older (≥ 65 years.) population. In the absence of clear guidelines on the appropriate use of the newer non-vitamin K antagonist oral anticoagulants in this population, this study specifically reviews the available literature for rivaroxaban and the impact of age that may affect the pharmacokinetics, pharmacodynamics, efficacy, and safety of this anticoagulant.

METHODS

This review includes a summary of data obtained from the available literature concerning both older healthy subjects and older patients with various aspects of cardiovascular disease enrolled in rivaroxaban clinical trials and data from real world evidence studies.

RESULTS

Evaluation of the clinical pharmacology in healthy, older adults reveal no clinically relevant effect of age on rivaroxaban pharmacokinetics and pharmacodynamics. Population pharmacokinetic studies in older patients with thromboembolic diseases suggest a moderate effect of increasing age on rivaroxaban clearance, albeit not clinically significant. Additionally, sub-group analyses from large, phase 3 clinical trials demonstrate consistent efficacy and safety in the older patient population vs the overall population. These findings are further supported by real-world evidence studies.

CONCLUSION

A favorable clinical profile with rivaroxaban was observed across age sub-groups, supporting the premise that dosing in older adults does not necessitate adjustment. However, it is prudent that a cautious and individualized approach is taken for treatment with any anticoagulant in older adults.

Influence of Renal Function on the Pharmacokinetics, Pharmacodynamics, Efficacy, and Safety of Non-Vitamin K Antagonist Oral Anticoagulants

With the growing integration of non-vitamin K antagonist oral anticoagulants (NOACs) into clinical practice, questions have arisen regarding their use in special populations, including groups that may have been underrepresented in clinical trials. Patients with renal impairment, particularly in the lower echelons of renal function, are one such group. In an effort to elucidate the current evidence regarding the use of NOACs in patients with renal impairment, a systematic assessment of the literature was performed. The MEDLINE database was interrogated for studies and analyses evaluating the influence of renal function on the pharmacokinetics, pharmacodynamics, efficacy, and safety of NOACs published from January 1, 2000, through August 2, 2017. The 82 relevant publications retrieved highlight the diversity in the NOAC class regarding the impact of renal function on drug clearance, drug exposures, and clinical trial outcomes. In several large clinical trials, subgroup analyses revealed no significant differences when patients were stratified by creatinine clearance as a measure of renal function. Efficacy findings, in particular, were largely aligned with the overall population in the included studies. However, relative risks of bleeding were shown to vary, sometimes driven by changes in bleeding event rates in the comparator arm (eg, warfarin, enoxaparin). With few exceptions, minimal influence of mild renal impairment was observed on the relative efficacy and safety of NOACs. Taken together, the evidence suggests that the presence of renal impairment merits careful consideration of anticoagulant choice but should not deter physicians from appropriate use of NOACs.

Integrated Population Pharmacokinetic Analysis of Rivaroxaban Across Multiple Patient Populations

The population pharmacokinetics (PK) of rivaroxaban have been evaluated in several population‐specific models. We developed an integrated population PK model using pooled data from 4,918 patients in 7 clinical trials across all approved indications. Effects of gender, age, and weight on apparent clearance (CL/F) and apparent volume of distribution (V/F), renal function, and comedication on CL/F, and relative bioavailability as a function of dose (F) were analyzed. Virtual subpopulations for exposure simulations were defined by age, creatinine clearance (CrCL) and body mass index (BMI). Rivaroxaban PK were adequately described by a one‐compartment disposition model with a first‐order absorption rate constant. Significant effects of CrCL, use of comedications, and study population on CL/F, age, weight, and gender on V/F, and dose on F were identified. CrCL had a modest influence on exposure, whereas age and BMI had a minor influence. The model was suitable to predict rivaroxaban exposure in patient subgroups of special interest.

Residual rivaroxaban exposure after discontinuation of anticoagulant therapy in patients undergoing cardiac catheterization

PURPOSE

Patients treated with direct oral anticoagulants (DOACs) frequently undergo interventional procedures requiring temporary discontinuation of anticoagulant therapy. Little is known about remaining peri-procedural exposure to rivaroxaban in real-world patients.

METHODS

Fifty-six patients with rivaroxaban treatment and scheduled cardiac catheterization were included in this prospective, observational, and single-center study. Rivaroxaban concentrations were determined by LC-MS/MS and a chromogenic anti-Xa assay. Population pharmacokinetic modeling was carried out on LC-MS/MS concentration data using NONMEM software, and results were applied to Monte Carlo simulations to predict appropriate rivaroxaban discontinuation intervals.

RESULTS

Rivaroxaban concentrations ranged from <LLOQ to 300.6 ng/ml at the time of admission to hospital and from <LLOQ to 55.5 ng/ml at the beginning of the procedure. Times since last rivaroxaban intake were (mean ± SD) 51.0 ± 31.7 h (admission) and 85.5 ± 36.8 h (start catheterization). LC-MS/MS and anti-Xa assay results were in good agreement (r = 0.958); however, the anti-Xa assay may underestimate low rivaroxaban concentrations and overestimate rivaroxaban exposure when performed on plasma samples contaminated with heparins. Pharmacokinetics of rivaroxaban were adequately described, and simulations predicted that 95% of patients will have rivaroxaban concentrations ≤ 28.4 ng/ml (15 mg dose group) and ≤ 31.9 ng/ml (20 mg dose group) after 48 h of discontinuation.

CONCLUSIONS

In the majority of patients, rivaroxaban plasma concentrations dropped below 30 ng/ml after 48 h of treatment discontinuation which is considered hemostatically safe before surgery with high bleeding risk. For accurate determination of low rivaroxaban concentrations, LC-MS/MS is the preferred choice.

The impact of body weight on rivaroxaban pharmacokinetics

BACKGROUND

There is concern amongst clinicians that the fixed dosing strategy of rivaroxaban for the treatment of venous thromboembolism (VTE) might not be optimal in those patients under or overweight.

OBJECTIVE

To develop a pharmacokinetic model for rivaroxaban, based on real-world patients, specifically focusing on the impact of patients' body weight on rivaroxaban pharmacokinetics.

PATIENTS/METHODS

One hundred and one patients prescribed rivaroxaban prophylactic or treatment doses for the prevention or treatment of VTE were recruited at a London teaching hospital. Subjects had up to 3 rivaroxaban concentrations measured during a single dosing period (trough, 1 and 3 hours post dose). Population pharmacokinetic analyses was conducted to develop a rivaroxaban model, which was subsequently evaluated.

RESULTS

A one-compartment model with between-subject variability on rivaroxaban clearance and volume of distribution, with a combined (additive and proportional) error model, best fitted the data. Following a full covariate analysis, creatinine clearance on rivaroxaban clearance was found to be the significant covariate impacting on the pharmacokinetic profile of rivaroxaban in the dataset.

CONCLUSIONS

Our results suggest that the most important covariate impacting on rivaroxaban pharmacokinetics is creatinine clearance and the weight alone has little effect. These findings are in line with previous studies for rivaroxaban. Larger datasets, from real-world patients who are followed longitudinally, should be conducted to provide front-line clinicians with further reassurance when prescribing rivaroxaban for the acute management of VTE.

Laboratory Assessment of the Anticoagulant Activity of Direct Oral Anticoagulants: A Systematic Review

BACKGROUND

Direct oral anticoagulants (DOACs) are the treatment of choice for most patients with atrial fibrillation and/or noncancer-associated venous thromboembolic disease. Although routine monitoring of these agents is not required, assessment of anticoagulant effect may be desirable in special situations. The objective of this review was to summarize systematically evidence regarding laboratory assessment of the anticoagulant effects of dabigatran, rivaroxaban, apixaban, and edoxaban.

METHODS

PubMed, Embase, and Web of Science were searched for studies reporting relationships between drug levels and coagulation assay results.

RESULTS

We identified 109 eligible studies: 35 for dabigatran, 50 for rivaroxaban, 11 for apixaban, and 13 for edoxaban. The performance of standard anticoagulation tests varied across DOACs and reagents; most assays, showed insufficient correlation to provide a reliable assessment of DOAC effects. Dilute thrombin time (TT) assays demonstrated linear correlation (r2 = 0.67-0.99) across a range of expected concentrations of dabigatran, as did ecarin-based assays. Calibrated anti-Xa assays demonstrated linear correlation (r2 = 0.78-1.00) across a wide range of concentrations for rivaroxaban, apixaban, and edoxaban.

CONCLUSIONS

An ideal test, offering both accuracy and precision for measurement of any DOAC is not widely available. We recommend a dilute TT or ecarin-based assay for assessment of the anticoagulant effect of dabigatran and anti-Xa assays with drug-specific calibrators for direct Xa inhibitors. In the absence of these tests, TT or APTT is recommended over PT/INR for assessment of dabigatran, and PT/INR is recommended over APTT for detection of factor Xa inhibitors. Time since last dose, the presence or absence of drug interactions, and renal and hepatic function should impact clinical estimates of anticoagulant effect in a patient for whom laboratory test results are not available.

Dosing of rivaroxaban by indication: getting the right dose for the patient

INTRODUCTION

Vitamin K antagonists were the only oral anticoagulants available for several decades, but they require frequent coagulation monitoring and dose adjustment. The direct oral anticoagulants rivaroxaban , dabigatran, apixaban, and, most recently, edoxaban have been approved for the management of specific thromboembolic indications.

AREAS COVERED

This review will provide a brief overview of the cell-based coagulation model, the main determinants of arterial and venous thrombosis, and the pharmacological rationale and clinical evidence for the different dosing regimens of rivaroxaban. Published articles indexed on PubMed and Medline covering arterial and venous thrombi pathophysiology, pharmacokinetics, and pharmacodynamics of rivaroxaban, and Phase II and Phase III clinical studies with rivaroxaban as well as real-world evidence were analyzed.

EXPERT OPINION

Education on pharmacokinetic/pharmacodynamic characteristics, as well as how to manage adverse events, is needed to increase physician knowledge and confidence in using direct oral anticoagulants, as specifically discussed for rivaroxaban in this article. The continued uptake of direct oral anticoagulants in clinical practice depends on understanding of the clinical evidence and reassurance provided by emerging real-world data.

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.

Rivaroxaban: a review of its use in acute coronary syndromes

Rivaroxaban (Xarelto(®)) is an orally administered highly selective direct inhibitor of factor Xa that has been approved in many countries to reduce the risk of stroke in patients with atrial fibrillation and for the treatment and prevention of venous thromboembolism. More recently, rivaroxaban at a low dosage of 2.5 mg twice daily, co-administered with aspirin alone or aspirin plus either clopidogrel or ticlopidine, was approved for use in the EU for patients with a recent acute coronary syndrome (ACS). The approval of rivaroxaban in ACS was primarily based on findings of the phase III ATLAS ACS 2-TIMI 51 trial, which showed that after a median of 13.1 months of treatment with rivaroxaban 2.5 mg twice daily (combined with aspirin or aspirin plus either clopidogrel or ticlopidine) there was a statistically significant reduction in the rate of the primary composite endpoint, which was death from cardiovascular causes, myocardial infarction or stroke, compared with placebo. Rivaroxaban 2.5 mg twice daily was also associated with a reduction in all-cause and cardiovascular mortality. There was an increase in the risk of major bleeding and intracranial haemorrhage with rivaroxaban 2.5 mg twice daily compared with placebo; however, there was no increase in the risk of fatal bleeding. Aspirin plus either ticagrelor or prasugrel was not evaluated as background dual antiplatelet therapy in ATLAS ACS 2-TIMI 51 and the safety implications of rivaroxaban used in combination with such therapy are unknown. In conclusion, results of the ATLAS ACS 2-TIMI 51 trial suggest a potentially important role for rivaroxaban 2.5 mg twice daily co-administered with aspirin alone or aspirin plus either clopidogrel or ticlopidine in patients with a recent ACS.

Peri-procedural use of rivaroxaban in elective percutaneous coronary intervention to treat stable coronary artery disease. The X-PLORER trial

Patients on rivaroxaban requiring percutaneous coronary intervention (PCI) represent a clinical conundrum. We aimed to investigate whether rivaroxaban, with or without an additional bolus of unfractionated heparin (UFH), effectively inhibits coagulation activation during PCI. Stable patients (n=108) undergoing elective PCI and on stable dual antiplatelet therapy were randomised (2:2:2:1) to a short treatment course of rivaroxaban 10 mg (n=30), rivaroxaban 20 mg (n=32), rivaroxaban 10 mg plus UFH (n=30) or standard peri-procedural UFH (n=16). Blood samples for markers of thrombin generation and coagulation activation were drawn prior to and at 0, 0.5, 2, 6-8 and 48 hours (h) after start of PCI. In patients treated with rivaroxaban (10 or 20 mg) and patients treated with rivaroxaban plus heparin, the levels of prothrombin fragment 1 + 2 at 2 h post-PCI were 0.16 [0.1] nmol/l (median) [interquartile range, IQR] and 0.17 [0.2] nmol/l, respectively. Thrombin-antithrombin complex values at 2 h post-PCI were 3.90 [6.8]µg/l and 3.90 [10.1] µg/l, respectively, remaining below the upper reference limit (URL) after PCI and stenting. This was comparable to the control group of UFH treatment alone. However, median values for thrombin-antithrombin complex passed above the URL with increasing tendency, starting at 2 h post-PCI in the UFH-alone arm but not in rivaroxaban-treated patients. In this exploratory trial, rivaroxaban effectively suppressed coagulation activation after elective PCI and stenting.

Effects of Rivaroxaban on Platelet Activation and Platelet-Coagulation Pathway Interaction: In Vitro and In Vivo Studies

Introduction:

Activation of coagulation and platelets is closely linked, and arterial thrombosis involves coagulation activation as well as platelet activation and aggregation. In these studies, we investigated the possible synergistic effects of rivaroxaban in combination with antiplatelet agents on thrombin generation and platelet aggregation in vitro and on arterial thrombosis and hemostasis in rat models.

Materials and Methods:

Thrombin generation was measured by the Calibrated Automated Thrombogram method (0.5 pmol/L tissue factor) using human platelet-rich plasma (PRP) spiked with rivaroxaban (15, 30, or 60 ng/mL), ticagrelor (1.0 µg/mL), and acetylsalicylic acid (ASA; 100 µg/mL). Tissue factor-induced platelet aggregation was measured in PRP spiked with rivaroxaban (15 or 30 ng/mL), ticagrelor (1 or 3 µg/mL), or a combination of these. An arteriovenous (AV) shunt model in rats was used to determine the effects of rivaroxaban (0.01, 0.03, or 0.1 mg/kg), clopidogrel (1 mg/kg), ASA (3 mg/kg), and combinations on arterial thrombosis.

Results:

Rivaroxaban inhibited thrombin generation in a concentration-dependent manner and the effect was enhanced with ticagrelor and ticagrelor plus ASA. Rivaroxaban and ticagrelor also concentration-dependently inhibited tissue factor-induced platelet aggregation, and their combination increased the inhibition synergistically. In the AV shunt model, rivaroxaban dose-dependently reduced thrombus formation. Combining subefficacious or weakly efficacious doses of rivaroxaban with ASA or ASA plus clopidogrel increased the antithrombotic effect.

Conclusion:

These data indicate that the combination of rivaroxaban with single or dual antiplatelet agents works synergistically to reduce platelet activation, which may in turn lead to the delayed/reduced formation of coagulation complexes and vice versa, thereby enhancing antithrombotic potency.

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.

Population pharmacokinetics and pharmacodynamics of rivaroxaban in patients with non-valvular atrial fibrillation: results from ROCKET AF

Two once-daily rivaroxaban dosing regimens were compared with warfarin for stroke prevention in patients with non-valvular atrial fibrillation in ROCKET AF: 20 mg for patients with normal/mildly impaired renal function and 15 mg for patients with moderate renal impairment. Rivaroxaban population pharmacokinetic (PK)/pharmacodynamic (PD) modeling data from ROCKET AF patients (n = 161) are reported and are used to confirm established rivaroxaban PK and PK/PD models and to re-estimate values of the models' parameters for the current AF population. An oral one-compartment model with first-order absorption adequately described rivaroxaban PK. Age, renal function, and lean body mass influenced the PK model. Prothrombin time and prothrombinase-induced clotting time exhibited a near-linear relationship with rivaroxaban plasma concentration; inhibitory effects were observed through to 24 hours post-dose. Rivaroxaban plasma concentration and factor Xa activity had an inhibitory maximum-effect (Emax ) relationship. Renal function (on prothrombin time; prothrombinase-induced clotting time) and age (on factor Xa activity) had moderate effects on PK/PD models. PK and PK/PD models were shown to be adequate for describing the current dataset. These findings confirm the modeling and empirical results that led to the selection of doses tested against warfarin in ROCKET AF.

Laboratory assessment of rivaroxaban: a review

Research into new anticoagulants for preventing and treating thromboembolic disorders has focused on targeting single enzymes in the coagulation cascade, particularly Factor Xa and thrombin, inhibition of which greatly decreases thrombin generation. Based on the results of phase III clinical trials, rivaroxaban, a direct Factor Xa inhibitor, has been approved in many countries for the management of several thromboembolic disorders. Owing to its predictable pharmacokinetic and pharmacodynamic characteristics, fixed-dose regimens are used without the need for routine coagulation monitoring. In situations where assessment of rivaroxaban exposure may be helpful, anti-Factor Xa chromogenic assays (in tandem with standard calibration curves generated with the use of rivaroxaban calibrators and controls) could be used. It is important to note that test results will be affected by the timing of blood sampling after rivaroxaban intake. In addition, the anti-Factor Xa method measures the drug concentration and not the intensity of the drug’s anticoagulant activity, and a higher than expected rivaroxaban plasma level does not necessarily indicate an increased risk of bleeding complications. Therefore, clinicians need to consider test results in relation to the pharmacokinetics of rivaroxaban and other patient risk factors associated with bleeding.

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.

Pharmacological Therapy in Stroke Prophylaxis - The New versus the Old Agents

Atrial fibrillation (AF) is the most common cardiac arrhythmia encountered in clinical practice. AF is a potent risk factor for stroke and systemic thromboembolism. Patients with AF have been observed to have a worse outcome following stroke, therefore prevention of stroke in patients with AF is of paramount importance. Antithrombotic therapy is crucial for prevention of stroke in patients with AF. Vitamin K antagonists (VKAs) have been the traditional anticoagulants for prevention of stroke in patients with AF. Drug treatment with VKAs is associated with significant management issues, such as an unpredictable dose response necessitating dose adjustments, frequent laboratory monitoring and multiple interactions with other drugs. Despite following best practices, VKAs are associated with limited efficacy and increased risk of hemorrhage. Due to these limitations a significant effort has been devoted towards development of newer anticoagulants. Dabigatran, Rivaroxaban, and more recently Apixaban have been approved by the F.D.A. for the prevention of stroke in patients with AF. These newer agents possess highly predictable pharmacokinetic and pharmacodynamics properties which allow a fixed dosing regimen and also eliminate the need of routine laboratory monitoring. This review discusses various anticoagulants for prevention of stroke in patients with AF.

Rivaroxaban: practical considerations for ensuring safety and efficacy

Rivaroxaban is the first agent available within a new class of anticoagulants called direct factor Xa inhibitors. Rivaroxaban is approved for use in the United States for the prevention of stroke and systemic embolism in patients with nonvalvular atrial fibrillation, for the prevention of deep vein thrombosis in patients undergoing total hip replacement and total knee replacement, for the treatment of deep vein thrombosis and pulmonary embolism, and for the reduction in risk of recurrence of deep vein thrombosis and pulmonary embolism (with additional indications under review). Rivaroxaban dose and frequency of administration vary depending on the indication. As of result of predictable pharmacokinetics and pharmacodynamics, a fixed dose of rivaroxaban is administered without routine coagulation testing. Rivaroxaban has a short half-life, undergoes a dual mode of elimination (hepatic and renal), and is a substrate for P-glycoprotein. Rivaroxaban has a lower potential for drug interactions compared with warfarin. Despite the advantages of a once/day fixed-dose oral agent, in many clinical situations limited evidence is available to guide optimal management of rivaroxaban therapy. In this article, we review the available evidence and provide recommendations where possible for such situations including the desire to monitor the anticoagulation intensity, use in special patient populations, managing drug interactions, and transitioning across anticoagulant agents. Potential strategies for reversing rivaroxaban's anticoagulant effect are reviewed. Health systems will need to perform a systematic safety evaluation and ensure that numerous hospital policies related to anticoagulation are updated to include rivaroxaban. A comprehensive approach to education is needed for clinicians, patients, and technical support personnel involved in patient interactions to ensure safe use.

Rivaroxaban for the treatment of acute coronary syndromes

INTRODUCTION

Recurrent ischemic events after an acute coronary syndrome (ACS) are frequent, despite current antiplatelet therapies and revascularization. Warfarin reduces recurrent ischemia but increases bleeding. Warfarin is difficult to administer with the proportion of time achieving therapeutic international normalized ratios varying within and among individuals. The newer oral anticoagulants have predictable dose-effect relationships and no monitoring is required.

AREAS COVERED

The pharmacology of rivaroxaban , evidence for the use of rivaroxaban in ACS, and the management of bleeding complications are covered in this article.

EXPERT OPINION

Arterial thrombosis is traditionally thought to be more platelet mediated than clotting factor mediated. Nonetheless, in the acute therapy for ACS, anticoagulation is a cornerstone treatment and there is persistent thrombin generation. Research has focused on finding a "sweet spot" of anticoagulation with high anti-ischemic and low bleeding effects. It follows that with chronic therapy post-ACS, there could also be a "sweet-spot" of anticoagulation. This may depend on the intrinsic vascular disease burden, the intervention delivered (stenting or bypass surgery), and background antiplatelet therapy. Rivaroxaban, a new oral factor Xa inhibitor, in a low-dose regimen-reduced ischemic events including mortality across a broad ACS population in the ATLAS-ACS trial with increased bleeding but without increasing fatal bleeding. Rivaroxaban is an attractive new treatment option for ACS.