Population pharmacokinetics and pharmacogenomics of apixaban in Japanese adult patients with atrial fibrillation

Circulating microRNAs and DNA Methylation as Regulators of Direct Oral Anticoagulant Response in Atrial Fibrillation and Key Elements for the Identification of the Mechanism of Action (miR-CRAFT): Study Design and Patient Enrolment

Direct oral anticoagulants (DOACs) are the standard treatment for thromboembolic protection in atrial fibrillation (AF) patients. Epigenetic modifications, such as DNA methylation and microRNAs, have emerged as potential biomarkers of AF. The epigenetics of DOACs is still an understudied field. It is largely unknown whether epigenetic modifications interfere with DOAC response or whether DOAC treatment induces epigenetic modifications. To fill this gap, we started the miR-CRAFT (Circulating microRNAs and DNA methylation as regulators of Direct Oral Anticoagulant Response in Atrial Fibrillation) research study. In miR-CRAFT, we follow, over time, changes in DNA methylation and microRNAs expression in naïve AF patients starting DOAC treatment. The ultimate goal of miR-CRAFT is to identify the molecular pathways epigenetically affected by DOACs, beyond the coagulation cascade, that are potentially mediating DOAC pleiotropic actions and to propose specific microRNAs as novel circulating biomarkers for DOAC therapy monitoring. We herein describe the study design and briefly present the progress in participant enrolment.

Gene polymorphism as a cause of hemorrhagic complications in patients with non-valvular atrial fibrillation treated with oral vitamin K-independent anticoagulants

Atrial fibrillation (AF) accounts for 40% of all cardiac arrhythmias and is associated with a high risk of stroke and systemic thromboembolic complications. Dabigatran, rivaroxaban, apixaban, and edoxaban are direct oral anticoagulants (DOACs) that have been proven to prevent stroke in patients with non-valvular AF. This review summarizes the pharmacokinetics, pharmacodynamics, and drug interactions of DOACs, as well as new data from pharmacogenetic studies of these drugs. This review is aimed at analyzing the scientific literature on the gene polymorphisms involved in the metabolism of DOACs. We searched PubMed, Cochrane, Google Scholar, and CyberLeninka (Russian version) databases with keywords: 'dabigatran', 'apixaban', 'rivaroxaban', 'edoxaban', 'gene polymorphism', 'pharmacogenetics', 'ABCB1', 'CES1', 'SULT1A', 'ABCG2', and 'CYP3A4'. The articles referred for this review include (1) full-text articles; (2) study design with meta-analysis, an observational study in patients taking DOAC; and (3) data on the single-nucleotide polymorphisms and kinetic parameters of DOACs (plasma concentration), or a particular clinical outcome, published in English and Russian languages during the last 10 years. The ages of the patients ranged from 18 to 75 years. Out of 114 reviewed works, 24 were found eligible. As per the available pharmacogenomic data, polymorphisms affecting DOACs are different. This may aid in developing individual approaches to optimize DOAC pharmacotherapy to reduce the risk of hemorrhagic complications. However, large-scale population studies are required to determine the dosage of the new oral anticoagulants based on genotyping. Information on the genetic effects is limited owing to the lack of large-scale studies. Uncovering the mechanisms of the genetic basis of sensitivity to DOACs helps in developing personalized therapy based on patient-specific genetic variants and improves the efficacy and safety of DOACs in the general population.

Population pharmacokinetics of apixaban in a real-life hospitalized population from the OptimAT study

This study aimed to characterize apixaban pharmacokinetics (PKs) and its variability in a real-world clinical setting of hospitalized patients using a population PK (PopPK) approach. Model-based simulations helped to identify factors that affect apixaban exposure and their clinical significance. A classic stepwise strategy was applied to determine the best PopPK model for describing typical apixaban PKs in hospitalized patients from the OptimAT study (n = 100) and evaluating the associated variability and influencing factors. Apixaban exposure under specific conditions was assessed using the final model. A two-compartment model with first-order absorption and elimination best described the data. The developed PopPK model revealed a major role of renal function and a minor role of P-glycoprotein phenotypic (P-gp) activity in explaining apixaban variability. The final model indicated that a patient with stage 4 chronic kidney disease (creatinine clearance [CLcr] = 15-29 mL/min) would have a 45% higher drug exposure than a patient with normal renal function (CLcr >90 mL/min), with a further 12% increase if the patient was also a poor metabolizer of P-gp. A high interindividual variability in apixaban PKs was observed in a real-life setting, which was partially explained by renal function and by P-gp phenotypic activity. Target apixaban concentrations are reached under standard dosage regimens, but overexposure can rapidly occur in the presence of cumulative factors warranting the development of a predictive tool for tailoring apixaban exposure and its clinical utility in at-risk patients.

ABCG2 Gene Polymorphisms May Affect the Bleeding Risk in Patients on Apixaban and Rivaroxaban

Purpose

Direct oral anticoagulants (DOACs) are widely used for stroke prevention in atrial fibrillation. However, they have a bleeding complication. Breast cancer resistance protein, encoded by ABCG2, is known to be an efflux transporter of apixaban and rivaroxaban among DOACs. This study aimed to investigate the association between gene variants and bleeding complications during treatment with ABCG2 substrates (apixaban and rivaroxaban).

Patients and Methods

Patients treated with apixaban and rivaroxaban were enrolled from June 2018 to December 2021. Five single nucleotide polymorphisms (SNPs) of ABCG2 were selected. Previously studied genes (ABCB1, CYP3A4, and CYP3A5) were further analyzed as possible confounders. Finally, a total of 16 SNPs were examined in this case-control study. The outcome was defined as major bleeding and clinically relevant non-major bleeding. Two models were constructed using the multivariable analysis.

Results

Among 293 patients, 64 were cases. The mean age of the patients was 68.8 years, and males comprised 62.5% of the study population. Model I revealed that a history of bleeding, concurrent use of proton pump inhibitor (PPI), ABCG2 rs3114018, and ABCB1 rs1045642 were significantly associated with bleeding complications; the AORs (95% CI) were 6.209 (2.210-17.442), 2.385 (1.064-5.349), 2.188 (1.156-4.142), and 3.243 (1.371-7.671), respectively. Model II showed that modified HAS-BLED score, concurrent use of PPI, ABCG2 rs3114018, and ABCB1 rs1045642 were significantly associated with bleeding complications.

Conclusion

The modified HAS-BLED score, a history of bleeding, concurrent use of PPI, ABCG2 rs3114018, and ABCB1 rs1045642 were significantly associated with the risk of bleeding complications in patients on apixaban and rivaroxaban, after adjusting for other confounders. These findings can be used to develop individualized treatment strategies for patients taking apixaban and rivaroxaban.

Impact of amiodarone on plasma concentration of direct oral anticoagulant in patients with atrial fibrillation

BACKGROUND/PURPOSE

Amiodarone increases exposure of direct oral anticoagulants (DOACs). We aimed to analyze the effects of concurrent amiodarone use on DOAC concentrations and clinical outcomes.

METHODS

Patients who were ≥20 years of age, had atrial fibrillation, and took DOAC were enrolled to provide trough and peak samples for DOAC concentration measurements using ultra-high-performance liquid chromatography-tandem mass spectrometry. The results were compared with concentrations reported in clinical trials to define above, within, or under the expected range. The outcomes of interest were major bleeding and any gastrointestinal bleeding. Multivariate logistic regression and Cox proportional hazards model were used to determine the impact of amiodarone on above-range concentration and clinical outcomes, respectively.

RESULTS

A total of 722 participants (420 men, 58.2%) were enrolled to provide 691 trough samples and 689 peak samples. Among them, 21.3% concurrently used amiodarone. The proportion of patients with above-range trough and peak concentrations was 16.4% and 30.2%, respectively, for amiodarone users, in contrast to 9.4% and 19.8% for amiodarone non-users. The use of amiodarone was associated with above-range trough and peak concentrations (odds ratio [OR] = 2.00 [1.16, 3.47] and 1.82 [1.19, 2.79], respectively). However, amiodarone was not a significant predictor of major bleeding or any gastrointestinal bleeding.

CONCLUSION

Concurrent amiodarone use led to increased DOAC concentration but was not associated with a higher risk of major bleeding or any gastrointestinal bleeding. Therapeutic monitoring of DOAC users concurrently taking amiodarone may be recommended for patients with an additional risk of increased DOAC exposure.

Identification of genetic biomarkers associated with pharmacokinetics and pharmacodynamics of apixaban in Chinese healthy volunteers

BACKGROUND

Apixaban is a superior direct oral anticoagulant exihibiting interindividual variability in concentration and response in the real world. The present study aimed to identify genetic biomarkers associated with pharmacokinetics (PK) and pharmacodynamics (PD) of apixaban in healthy Chinese subjects.

METHODS

This multicenter study included 181 healthy Chinese adults taking a single dose of 2.5 mg or 5 mg apixaban and assessed their PK and PD parameters. Genome-wide single nucleotide polymorphism (SNP) genotyping was performed using the Affymetrix Axiom CBC_PMRA Array. Candidate gene association analysis and genome-wide association study were conducted to identify genes with a predictive value for PK and PD parameters of apixaban.

RESULTS

Several ABCG2 variants were associated with C_max and AUC_0-t of apixaban (p < 6.12 × 10^-5) and also presented significant differences of anti-Xa_3h activity and dPT_3h according to different ABCG2 genotypes (p < 0.05). Besides, ABLIM2 variants were found to be associated with PK characteristics and F13A1 and C3 variants were associated with PD characteristics of apixaban (p < 9.46 × 10^-8).

CONCLUSION

ABCG2 variants were found to be ideal genetic biomarkers for both PK and PD characteristics of apixaban. ABLIM2, F13A1 and C3 were identified as potential candidate genes associated with inter-individual variability of apixaban. This study was registered on ClinicalTrials.gov NCT03259399.

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.

Personalizing Direct Oral Anticoagulant Therapy for a Diverse Population: Role of Race, Kidney Function, Drug Interactions, and Pharmacogenetics

Oral anticoagulants (OACs) are commonly used to reduce the risk of venous thromboembolism and the risk of stroke in patients with atrial fibrillation. Endorsed by the American Heart Association, American College of Cardiology, and the European Society of Cardiology, direct oral anticoagulants (DOACs) have displaced warfarin as the OAC of choice for both conditions, due to improved safety profiles, fewer drug-drug and drug-diet interactions, and lack of monitoring requirements. Despite their widespread use and improved safety over warfarin, DOAC-related bleeding remains a major concern for patients. DOACs have stable pharmacokinetics and pharmacodynamics; however, variability in DOAC response is common and may be attributed to numerous factors, including patient-specific factors, concomitant medications, comorbid conditions, and genetics. Although DOAC randomized controlled trials included patients of varying ages and levels of kidney function, they failed to include patients of diverse ancestries. Additionally, current evidence to support DOAC pharmacogenetic associations have primarily been derived from European and Asian individuals. Given differences in genotype frequencies and disease burden among patients of different biogeographic groups, future research must engage diverse populations to assess and quantify the impact of predictors on DOAC response. Current under-representation of patients from diverse racial groups does not allow for proper generalization of the influence of clinical and genetic factors in relation to DOAC variability. Herein, we discuss factors affecting DOAC response, such as age, sex, weight, kidney function, drug interactions, and pharmacogenetics, while offering a new perspective on the need for further research including frequently excluded groups.

Safety, pharmacokinetics and exploratory exposure-response analysis of CX3002, a novel inhibitor of Xa, in Chinese healthy subjects

BACKGROUND AND OBJECTIVE

CX3002 is a structurally novel inhibitor of factor Xa, with promising prospects. This study aims to report the results of a first-in-human ascending-dose study of CX3002 in Chinese healthy subjects, and to establish an exploratory population pharmacokinetic/pharmacodynamic (PK/PD) model to investigate the exposure-response relationship of CX3002.

METHODS

The randomized, double-blind, placebo-controlled study included six single-dose groups and three multiple-dose groups, with a dose range of 1-30 mg. Safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of CX3002 were evaluated. PK of CX3002 was analyzed using both non-compartment method and population modeling. PK/PD model was developed using nonlinear mixed effect modeling approach and was evaluated by prediction-corrected visual predictive check and bootstrap methods.

RESULTS

A total of 84 subjects were enrolled and all participants completed the study. CX3002 exhibited satisfactory safety and tolerability in healthy subjects. C_max and AUC of CX3002 increased with dose from 1 mg to 30 mg, but less-than-proportional increases were observed. There was no obvious accumulation with multiple doses. Anti-Xa activity showed dose-related increases after administration of CX3002 but not placebo. The PK of CX3002 was well described by a two-compartment model with a modification of bioavailability according to dose, and anti-Xa activity was described by a Hill function. No covariate was identified significant based on the limited data in this study.

CONCLUSIONS

CX3002 was well tolerated and resulted in dose-related anti-Xa activity across the dose range. The PK of CX3002 were predictable, and correlated with PD effects. Continued clinical investigation of CX3002 was supported. Chinadrugtrials.org.cn identifier: CTR20190153.

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.

Impacts of pregnane X receptor and cytochrome P450 oxidoreductase gene polymorphisms on trough concentrations of apixaban in patients with non-valvular atrial fibrillation

PURPOSE

We examined the impact of polymorphisms in genes encoding cytochrome P450 (CYP) 3A5 (gene code CYP3A5), P-glycoprotein (ABCB1), breast cancer resistance protein (ABCG2), cytochrome P450 oxidoreductase (POR), and pregnane X receptor (PXR; NR1I2) on the daily dose-adjusted steady-state trough concentrations (C_0h/D) of apixaban.

METHODS

The analyses included 104 patients with non-valvular atrial fibrillation (NVAF) undergoing AF catheter ablation. The CYP3A5*3; ABCG2 421C > A; ABCB1 1236C > T, 2677G > A/T, 3435C > T, and 2482-2236G > A; NR1I2 11156A > C, 11193T > C, and 8055C > T; and POR*28 genotypes were determined. The combination of the noted NR1I2 genotypes determined the PXR*1B haplotype.

RESULTS

Multiple linear regression analyses demonstrated that decreased creatinine clearance (Ccr) and the PXR*1B/*1B haplotype correlated with increased C_0h/D of apixaban, while the presence of the POR*28 allele correlated with decreased C_0h/D of apixaban (partial R² = 0.168, 0.029, and 0.044, all P < 0.05). The mean (95% CI) of estimated marginal means of apixaban C_0h/D calculated using Ccr as a covariate was the highest in POR*28 noncarriers with PXR*1B/*1B (23.5 [21.0-25.9] ng/mL/[mg/day]) and lowest in POR*28 carriers with other haplotypes (16.6 [15.5-17.7] ng/mL/[mg/day]).

CONCLUSION

The PXR*1B haplotype and POR*28 genotype statuses, which involve genes that impact the expression of multiple drug-metabolizing enzymes and drug-transporters, may have modest effects on the C_0h/D of apixaban, but these effects were found to be small.

ABCG2 and SLCO1B1 gene polymorphisms in the Croatian population

BACKGROUND

Organic anion-transporting polypeptide 1B1 (OATP1B1) and the ATP-binding cassette subfamily G member 2, ABCG2, are important transporters involved in the transport of endogenous substrates and xenobiotics, including drugs. Genetic polymorphisms of these transporters have effect on transporter activity. There is significant interethnic variability in the frequency of allele variants.

AIM

To determined allele and genotype frequencies of ABCG2 and SLCO1B1 genes in Croatian populations of European descent.

SUBJECTS AND METHODS

A total of 905 subjects (482 women) were included. Genotyping for ABCG2 c.421C > A (rs2231142) and for SLCO1B1 c.521T > C (rs4149056), was performed by real-time polymerase chain reaction (PCR) using TaqMan^® DME Genotyping Assays.

RESULTS

For ABCG2 c.421C > A, the frequency of CC, CA and AA genotypes was 81.4%, 17.8% and 0.8% respectively. The frequency of variant ABCG2 421 A allele was 9.7%. For SLCO1B1 c.521T > C, the frequency of TT, TC and CC genotypes was 61.7%, 34.8% and 3.5% respectively. The frequency of variant SLCO1B1 521 C allele was 20.9%.

CONCLUSION

The frequency of the ABCG2 and SLCO1B1 allelic variants and genotypes in the Croatian population is in accordance with other European populations. Pharmacogenetic analysis can serve to individualise drug therapy and minimise the risk of developing adverse drug reactions.

Eight pharmacokinetic genetic variants are not associated with the risk of bleeding from direct oral anticoagulants in non-valvular atrial fibrillation patients

Background: Atrial fibrillation (AF) is the leading cause of ischemic stroke and treatment has focused on reducing this risk through anticoagulation. Direct Oral Anticoagulants (DOACs) are the first-line guideline-recommended therapy since they are as effective and overall safer than warfarin in preventing AF-related stroke. Although patients bleed less from DOACs compared to warfarin, bleeding remains the primary safety concern with this therapy. Hypothesis: Genetic variants known to modify the function of metabolic enzymes or transporters involved in the pharmacokinetics (PK) of DOACs could increase the risk of bleeding. Aim: To assess the association of eight, functional PK-related single nucleotide variants (SNVs) in five genes (ABCB1, ABCG2, CYP2J2, CYP3A4, CYP3A5) with the risk of bleeding from DOACs in non-valvular AF patients. Methods: A retrospective cohort study was carried out with 2,364 self-identified white non-valvular AF patients treated with either rivaroxaban or apixaban. Genotyping was performed with Illumina Infinium CoreExome v12.1 bead arrays by the Michigan Genomics Initiative biobank. The primary endpoint was a composite of major and clinically relevant non-major bleeding. Cox proportional hazards regression with time-varying analysis assessed the association of the eight PK-related SNVs with the risk of bleeding from DOACs in unadjusted and covariate-adjusted models. The pre-specified primary analysis was the covariate-adjusted, additive genetic models. Six tests were performed in the primary analysis as three SNVs are in the same haplotype, and thus p-values below the Bonferroni-corrected level of 8.33e-3 were considered statistically significant. Results: In the primary analysis, none of the SNVs met the Bonferroni-corrected level of statistical significance (all p > 0.1). In exploratory analyses with other genetic models, the ABCB1 (rs4148732) GG genotype tended to be associated with the risk of bleeding from rivaroxaban [HR: 1.391 (95%CI: 1.019-1.900); p = 0.038] but not from apixaban (p = 0.487). Conclusion: Eight functional PK-related genetic variants were not significantly associated with bleeding from either rivaroxaban or apixaban in more than 2,000 AF self-identified white outpatients.

Genetic determinants of apixaban plasma levels and their relationship to bleeding and thromboembolic events

Apixaban is a direct oral anticoagulant, a factor Xa inhibitor, used for the prevention of ischemic stroke in patients with atrial fibrillation. Despite using recommended dosing a few patients might still experience bleeding or lack of efficacy that might be related to inappropriate drug exposure. We conducted a genome-wide association study using data from 1,325 participants in the pivotal phase three trial of apixaban with the aim to identify genetic factors affecting the pharmacokinetics of apixaban. A candidate gene analysis was also performed for pre-specified variants in ABCB1, ABCG2, CYP3A4, CYP3A5, and SULT1A1, with a subsequent analysis of all available polymorphisms within the candidate genes. Significant findings were further evaluated to assess a potential association with clinical outcome such as bleeding or thromboembolic events. No variant was consistently associated with an altered apixaban exposure on a genome-wide level. The candidate gene analyses showed a statistically significant association with a well-known variant in the drug transporter gene ABCG2 (c.421G &gt; T, rs2231142). Patients carrying this variant had a higher exposure to apixaban [area under the curve (AUC), beta = 151 (95% CI 59–243), p = 0.001]. On average, heterozygotes displayed a 5% increase of AUC and homozygotes a 17% increase of AUC, compared with homozygotes for the wild-type allele. Bleeding or thromboembolic events were not significantly associated with ABCG2 rs2231142. This large genome-wide study demonstrates that genetic variation in the drug transporter gene ABCG2 is associated with the pharmacokinetics of apixaban. However, the influence of this finding on drug exposure was small, and further studies are needed to better understand whether it is of relevance for ischemic and bleeding events.

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.

Urine volume to hydration volume ratio is associated with pharmacokinetics of high-dose methotrexate in patients with primary central nervous system lymphoma

High-dose methotrexate (HD-MTX)-based chemotherapy is the first-line treatment for primary central nervous system lymphoma (PCNSL), but is associated with severe adverse effects, including myelosuppression and renal impairment. MTX is primarily excreted by the kidneys. Renal function calculated using serum creatinine (Scr) derived from muscle may be overestimated in elderly PCNSL patients. Therefore, we aimed to construct a population pharmacokinetic model in PCNSL patients and explore the factors associated with MTX clearance. Sixteen PCNSL patients (median age, 66 years) treated with HD-MTX were included, and serum MTX concentrations were measured at 193 points in 49 courses. A population pharmacokinetic analysis was performed using NONMEM. A Monte Carlo simulation was conducted, in which serum MTX concentrations were stratified into three groups of creatine clearance (Ccr) (50, 75, and 100 ml/min) with three groups of the urine volume to hydration volume (UV/HV) ratio (<1, 1-2, and >2). The final model was constructed as follows: MTX clearance = 4.90·(Ccr/94.5)0.456 ·(UV/HV)0.458 . In the Monte Carlo simulation, serum MTX concentrations were below the standard values (10, 1, and 0.1 µM at 24, 48, and 72 h, respectively, after the start of the MTX administration) in most patients with UV/HV >2, even with Ccr of 50 ml/min. Conversely, half of the patients with UV/HV <1 and Ccr of 50 ml/min failed to achieve the standard values. The present results demonstrated that the UV/HV ratio was useful for describing the pharmacokinetics of MTX in PCNSL patients.

Variation in Expression of Cytochrome P450 3A Isoforms and Toxicological Effects: Endo- and Exogenous Substances as Regulatory Factors and Substrates

The CYP3A subfamily, which includes isoforms CYP3A4, CYP3A5, and CYP3A7 in humans, plays important roles in the metabolism of various endogenous and exogenous substances. Gene and protein expression of CYP3A4, CYP3A5, and CYP3A7 show large inter-individual differences, which are caused by many endogenous and exogenous factors. Inter-individual differences can cause negative outcomes, such as adverse drug events and disease development. Therefore, it is important to understand the variations in CYP3A expression caused by endo- and exogenous factors, as well as the variation in the metabolism and kinetics of endo- and exogenous substrates. In this review, we summarize the factors regulating CYP3A expression, such as bile acids, hormones, microRNA, inflammatory cytokines, drugs, environmental chemicals, and dietary factors. In addition, variations in CYP3A expression under pathological conditions, such as coronavirus disease 2019 and liver diseases, are described as examples of the physiological effects of endogenous factors. We also summarize endogenous and exogenous substrates metabolized by CYP3A isoforms, such as cholesterol, bile acids, hormones, arachidonic acid, vitamin D, and drugs. The relationship between the changes in the kinetics of these substrates and the toxicological effects in our bodies are discussed. The usefulness of these substrates and metabolites as endogenous biomarkers for CYP3A activity is also discussed. Notably, we focused on discrimination between CYP3A4, CYP3A5, and CYP3A7 to understand inter-individual differences in CYP3A expression and function.

Comparison of the Safety and Effectiveness of Four Direct Oral Anticoagulants in Japanese Patients with Nonvalvular Atrial Fibrillation Using Real-World Data

Direct oral anticoagulants (DOACs) are widely used for the prevention of ischemic stroke and systemic embolism in patients with nonvalvular atrial fibrillation (NVAF). However, the differences in safety and effectiveness among four DOACs, dabigatran, rivaroxaban, apixaban, and edoxaban, in Japanese patients have not been clarified. Therefore, we conducted a retrospective cohort study to directly compare the safety and effectiveness among the four DOACs using the Japan Medical Data Center (JMDC) claims database. We identified 3823 patients with NVAF who started receiving a DOAC between March 2011 and June 2017. The safety outcome was major bleeding (a composite outcome of intracranial, gastrointestinal, respiratory, or renal/urinary tract bleeding) and the effectiveness outcome was the composite of ischemic stroke including transient ischemic attack (TIA) or systemic embolism. We constructed a Cox proportional hazard model to calculate the hazard ratio (HR) for all four DOAC combinations. The risk of major bleeding was significantly lower in the dabigatran group than in the apixaban group (HR, 0.55; 95% confidence interval (CI), 0.31-0.93; p = 0.03). In contrast, there was no significant difference in the risk of major bleeding among the other DOACs. In the composite risk of ischemic stroke including TIA or systemic embolism, there was no significant difference among the four DOACs. This study suggested that in the current use of DOACs in Japanese patients with NVAF, dabigatran had a significantly lower risk of major bleeding than apixaban, but there was no significant difference in effectiveness among the four DOACs.

Pharmacogenetics of Bleeding and Thromboembolic Events in Direct Oral Anticoagulant Users

This study aimed to analyze associations between genetic variants and the occurrence of clinical outcomes in dabigatran, apixaban, and rivaroxaban users. This was a retrospective real-world study linking genotype data of three Finnish biobanks with national register data on drug dispensations and healthcare encounters. We investigated several single-nucleotide variants (SNVs) in the ABCG2, ABCB1, CES1, and CYP3A5 genes potentially associated with bleeding or thromboembolic events in direct oral anticoagulant (DOAC) users based on earlier research. We used Cox regression models to compare the incidence of clinical outcomes between carriers and noncarriers of the SNVs or haplotypes. In total, 1,806 patients on apixaban, dabigatran, or rivaroxaban were studied. The ABCB1 c.3435C>T (p.Ile1145=, rs1045642) SNV (hazard ratio (HR) 0.42, 95% confidence interval (CI), 0.18-0.98, P = 0.044) and 1236T-2677T-3435T (rs1128503-rs2032582-rs1045642) haplotype (HR 0.44, 95% CI, 0.20-0.95, P = 0.036) were associated with a reduced risk for thromboembolic outcomes, and the 1236C-2677G-3435C (HR 2.55, 95% CI, 1.03-6.36, P = 0.044) and 1236T-2677G-3435C (HR 5.88, 95% CI, 2.35-14.72, P < 0.001) haplotypes with an increased risk for thromboembolic outcomes in rivaroxaban users. The ABCB1 c.2482-2236G>A (rs4148738) SNV associated with a lower risk for bleeding events (HR 0.37, 95% CI, 0.16-0.89, P = 0.025) in apixaban users. ABCB1 variants are potential factors affecting thromboembolic events in rivaroxaban users and bleeding events in apixaban users. Studies with larger numbers of patients are warranted for comprehensive assessment of the pharmacogenetic associations of DOACs and their relevance for clinical practice.

ABCB1, ABCG2, ABCC1, ABCC2, and ABCC3 drug transporter polymorphisms and their impact on drug bioavailability: what is our current understanding?

INTRODUCTION

Interindividual differences in drug response are a frequent clinical challenge partly due to variation in pharmacokinetics. ATP-binding cassette (ABC) transporters are crucial determinants of drug disposition. They are subject of gene regulation and drug-interaction; however, it is still under debate to which extend genetic variants in these transporters contribute to interindividual variability of a wide range of drugs.

AREAS COVERED

This review discusses the current literature on the impact of genetic variants in ABCB1, ABCG2 as well as ABCC1, ABCC2, and ABCC3 on pharmacokinetics and drug response. The aim was to evaluate if results from recent studies would increase the evidence for potential clinically relevant pharmacogenetic effects.

EXPERT OPINION

Although enormous efforts have been made to investigate effects of ABC transporter genotypes on drug pharmacokinetics and response, the majority of studies showed only weak if any associations. Despite few unique results, studies mostly failed to confirm earlier findings or still remained inconsistent. The impact of genetic variants on drug bioavailability is only minor and other factors regulating the transporter expression and function seem to be more critical. In our opinion, the findings on the so far investigated genetic variants in ABC efflux transporters are not suitable as predictive biomarkers.

Pharmacogenetics of tamoxifen therapy in Asian populations: from genetic polymorphism to clinical outcomes

BACKGROUND

Compared with western countries, Asian breast cancer patients have unique pathological and biological characteristics. Most of them are premenopausal women with HR positive. Tamoxifen as the first-line drug for premenopausal women with HR+ is involved in multiple enzymes and transporters during metabolizing and transporting process. Variants that cause decreased or inactive gene products leading to abnormal responses in tamoxifen therapy have well been studied in western countries, whereas such information is much less reported in Asian populations.

OBJECTIVE

In order to elucidate the relationship between genetic variants and tamoxifen-induced individual drug reactions in different Asian populations and further identify genotypes/phenotypes with potential therapeutic significance.

METHODS

We reviewed the frequencies of genetic variants in major enzymes and transporter genes involved in the metabolism and transport of tamoxifen across Asian populations as well as significant correlations between genotypes/metabolic phenotypes and metabolites concentrations or BC clinical outcomes.

RESULTS

Significant inter-ethnic differences in allele frequencies was found among Asian populations, such as CYP2D6*4, *10, *41, CYP2C9*2, ABCB1 C3435T and SLCO1B1*5, and CYP2D6*10/*10 is the most common genotype correlated with adverse clinical outcomes. Moreover, we summarized the barriers and controversies of implementing pharmacogenetics in tamoxifen therapy and concluded that more population-specific pharmacogenetic studies are needed in the future.

CONCLUSION

This review revealed more systematic pharmacogenomics of genes involved in the metabolism and transport besides CYP2D6, are required to optimize the genotyping strategies and guide the personalized tamoxifen therapy in Asian populations.

Drug interactions and pharmacogenetic factors contribute to variation in apixaban concentration in atrial fibrillation patients in routine care

Factor Xa-inhibitor apixaban is an oral anticoagulant prescribed in atrial fibrillation (AF) for stroke prevention. Its pharmacokinetic profile is known to be affected by cytochrome P450 (CYP)3A metabolism, while it is also a substrate of the efflux transporters ATP-binding cassette (ABC)B1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein, BCRP). In this study, we assessed the impact of interacting medication and pharmacogenetic variation to better explain apixaban concentration differences among 358 Caucasian AF patients. Genotyping (ABCG2, ABCB1, CYP3A4*22, CYP3A5*3) was performed by TaqMan assays, and apixaban quantified by mass spectrometry. The typical patient was on average 77.2 years old, 85.5 kg, and had a serum creatinine of 103.1 µmol/L. Concomitant amiodarone, an antiarrhythmic agent and moderate CYP3A/ABCB1 inhibitor, the impaired-function variant ABCG2 c.421C > A, and sex predicted higher apixaban concentrations when controlling for age, weight and serum creatinine (multivariate regression; R² = 0.34). Our findings suggest that amiodarone and ABCG2 genotype contribute to interpatient apixaban variability beyond known clinical factors.

Pharmacokinetics and Pharmacogenetics of Apixaban

Apixaban is oral anticoagulant, it is widely used in prevention of stroke in non-valvular atrial fibrillation and treatment of deep vein thrombosis and pulmonary embolism. Its main mechanism of action is through reversible inhibition of factor Xa. It specifically binds and inhibits both free and bound factor Xa which ultimately results in reduction in the levels of thrombin formation. Apixaban is mainly metabolized by CYP3A4 with minor contributions from CYP1A2, CYP2C8, CYP2C9, CYP2C19 and CYP2J2 isoenzymes. Some of the major metabolic pathways of apixaban include o-demethylation, hydroxylation, and sulfation, with o-demethylapixabansulphate being the major metabolite. The aim of this review is analysis of associated researches of single nucleotide variants (SNV) of CYP3A5 and SULT1A1 genes and search for new candidate genes reflecting effectiveness and safety of apixaban. The search for full-text publications in Russian and English languages containing key words “apixaban”, “pharmacokinetics”, “effectiveness”, “safety” was carried out amongst literature of the past twenty years with the use of eLibrary, PubMed, Web of Science, OMIM data bases. Pharmacokinetics and pharmacogenetics of apixaban are considered in this review. The hypothesis about CYP и SULT1A enzymes influence on apixaban metabolism was examined. To date, numerous SNVs of the CYP3A5 and SULT1A1 genes have been identified, but their potential influence on pharmacokinetics apixaban in clinical practice needs to be further studies. The role of SNVs of other genes encoding beta-oxidation enzymes of apixaban (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2J2) and transporter proteins (ABCB1, ABCG2) in its efficacy and safety are not well understood, and ABCB1 and ABCG2 genes may be potential candidate genes for studies of the drug safety.

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.

Apixaban: A Clinical Pharmacokinetic and Pharmacodynamic Review

Apixaban is an oral, direct factor Xa inhibitor that inhibits both free and clot-bound factor Xa, and has been approved for clinical use in several thromboembolic disorders, including reduction of stroke risk in non-valvular atrial fibrillation, thromboprophylaxis following hip or knee replacement surgery, the treatment of deep vein thrombosis or pulmonary embolism, and prevention of recurrent deep vein thrombosis and pulmonary embolism. The absolute oral bioavailability of apixaban is ~ 50%. Food does not have a clinically meaningful impact on the bioavailability. Apixaban exposure increases dose proportionally for oral doses up to 10 mg. Apixaban is rapidly absorbed, with maximum concentration occurring 3–4 h after oral administration, and has a half-life of approximately 12 h. Elimination occurs via multiple pathways including metabolism, biliary excretion, and direct intestinal excretion, with approximately 27% of total apixaban clearance occurring via renal excretion. The pharmacokinetics of apixaban are consistent across a broad range of patients, and apixaban has limited clinically relevant interactions with most commonly prescribed medications, allowing for fixed dosages without the need for therapeutic drug monitoring. The pharmacodynamic effect of apixaban is closely correlated with apixaban plasma concentration. This review provides a summary of the pharmacokinetic, pharmacodynamic, biopharmaceutical, and drug–drug interaction profiles of apixaban. Additionally, the population-pharmacokinetic analyses of apixaban in both healthy subjects and in the target patient populations are discussed.

Unexpected excessive apixaban exposure: case report of a patient with polymorphisms of multiple apixaban elimination pathways

Background

Apixaban effectively lowers the risk of ischemic stroke and systemic embolism in patients with non-valvular atrial fibrillation. Systemic exposure to a given apixaban dose depends on multiple clearance pathways. Though routine quantification of direct oral anticoagulants (DOACs) in neurological emergency situations has not been widely established, suspected associations of DOAC peak concentrations with bleeding events and DOAC trough concentrations with efficacy and safety suggest that such information might support clinical decision making.

Case presentation

We describe the case of a 75 year-old woman with atrial fibrillation maintained on apixaban who was admitted due to suspected acute stroke. Clinical work-up did not confirm ischemic or hemorrhagic stroke but routine quantification of apixaban revealed an excessively high apixaban plasma concentration (~ 3 h after the last drug intake: 1100 ng/ml (expected range: 91–321 ng/ml); ~ 12 h after drug intake: 900 ng/ml (expected range: 41–230 ng/ml)) and a substantially prolonged elimination half-life (~ 31 h). The corresponding apixaban concentration-to-dose ratio was 9900 (ng/ml)/(mg/kg/d) and 8100 (ng/ml)/(mg/kg/d), respectively (expected range: 249–463 (ng/ml)/(mg/kg/d)). Renal function was only moderately impaired (creatinine 1.36 mg/dl (0.5–1.1 mg/dl), creatinine clearance 40 ml/min). Genotype analyses revealed that the patient was a CYP3A5*3/*3 non-expressor, a heterozygous carrier of the ABCG2 c.421C/A alleles, and a homozygous carrier of ABCB1 c.2677 T/T and ABCB1 c.3435 T/T. In the absence of known drug interactions explaining apixaban clearance impairment, excessive apixaban concentrations were most probably caused by moderate renal impairment combined with multiple functional polymorphisms of apixaban clearance pathways.

Conclusions

This case suggests that concurrent genetic polymorphisms can impair multiple apixaban elimination pathways and thus substantially increase its exposure.

Population Pharmacokinetics and Pharmacodynamics of Apixaban Linking Its Plasma Concentration to Intrinsic Activated Coagulation Factor X Activity in Japanese Patients with Atrial Fibrillation

Apixaban is used in the prevention and treatment of patients with deep vein thrombosis or pulmonary embolism, and in the prevention of stroke or systemic embolism in patients with nonvalvular atrial fibrillation (AF). In this study, we aimed to elucidate intrinsic factors affecting efficacy of apixaban by conducting population pharmacokinetic and pharmacodynamic analysis using data from 81 Japanese AF patients. The intrinsic FXa activity was determined to assess the pharmacodynamic effect of apixaban. The pharmacokinetic and pharmacodynamic profiles were described based on a one-compartment model with first-order absorption and a maximum inhibitory model, respectively. Pharmacokinetic and pharmacodynamic analysis was conducted using a nonlinear mixed effect modeling program. The population pharmacokinetic parameters of apixaban were fixed at the reported values in our recent study. The population mean of half-maximal inhibitory concentration (IC₅₀) of apixaban was estimated to be 45.3 ng/mL. The population mean IC₅₀ decreased 27.7% for patients with heart failure, but increased 55% for patients with a medical history of cerebral infarction. In contrast, no covariates affected the population mean of baseline of intrinsic FXa activity (BASE) and maximum effect (I_max) value of apixaban. The population mean of BASE and I_max value were estimated to be 40.2 and 38.4 nmol/min/mg protein, respectively. The present study demonstrates for the first time that the co-morbidity of heart failure as well as the medical history of cerebral infarction are an intrinsic factor affecting the pharmacodynamics of apixaban.

Population pharmacokinetics and pharmacogenomics of apixaban in Japanese adult patients with atrial fibrillation

AIMS

This study aimed to analyse the effects of genetic polymorphisms in drug transporters and metabolizing enzymes, and clinical laboratory data on the pharmacokinetic parameters of apixaban.

METHODS

Data were collected from 81 Japanese patients with atrial fibrillation. Pharmacogenomic data were stratified by ABCB1, ABCG2 and CYP3A5 polymorphisms. The pharmacokinetic profile of apixaban was described by a one-compartment model with first-order absorption. Population pharmacokinetic analysis was conducted using a nonlinear mixed effect modelling (NONMEM™) program.

RESULTS

The nonlinear relationship between oral clearance (CL/F) of apixaban and creatinine clearance (Ccr) was observed. The population mean of CL/F for a typical patient (Ccr value of 70 ml min^-1 ) with the CYP3A5*1/*1 and ABCG2 421C/C or C/A genotypes was estimated to be 3.06 l h^-1 . When Ccr values were set to the typical value, the population mean of CL/F was 1.52 times higher in patients with the CYP3A5*1/*1 genotype compared with patients with the CYP3A5*1/*3 or *3/*3 genotype, while the population mean of CL/F was 1.49 times higher in patients with the ABCG2 421C/C or C/A genotype compared with patients with the ABCG2 421A/A genotype. However, no covariates affected the population mean of the apparent volume of distribution (Vd/F) of apixaban. The population mean of Vd/F was estimated to be 24.7 l.

CONCLUSION

The present study suggests that the ABCG2 421A/A and CYP3A5*3 genotypes and renal function are intrinsic factors affecting apixaban pharmacokinetics. These findings may provide useful information for precision medicine using apixaban, to avoid the risk of adverse reactions.