Cost-Effectiveness Analysis of Pharmacogenomics (PGx)-Based Warfarin, Apixaban, and Rivaroxaban Versus Standard Warfarin for the Management of Atrial Fibrillation in Ontario, Canada.

OBJECTIVE: To assess the cost-effectiveness of pharmacogenomics (PGx)-based warfarin (i.e., warfarin dosing following genetic testing), apixaban, and rivaroxaban oral anticoagulation versus standard warfarin for the treatment of newly diagnosed patients with nonvalvular atrial fibrillation (AF) aged ≥ 65 years. METHODS: We developed a Markov decision-analytic model to compare costs [2017 Canadian dollars (C$)] and quality-adjusted life years (QALYs) from the Ontario health care payer perspective over a life-time horizon. The parameters used in the model were derived from the published literature, the Ontario health care administrative database, and expert opinion. To account for the uncertainty of model parameters, we conducted extensive deterministic and probabilistic sensitivity analyses. The results were summarized using incremental cost-effectiveness ratios (ICERs) and cost-effectiveness acceptability curves. RESULTS: We found that PGx-based warfarin had an ICER of C$17,584/QALY compared with standard warfarin, and apixaban had an ICER of C$64,590/QALY compared with PGx-based warfarin in our base-case analysis. Rivaroxaban was extendedly dominated by PGx-based warfarin and apixaban. The probabilistic sensitivity analysis showed that apixaban, rivaroxaban, PGx-based warfarin, and standard warfarin were cost-effective at some willingness-to-pay (WTP) thresholds. PGx-based warfarin had a higher probability of being cost-effective than apixaban (51.3% versus 14.3%) at a WTP threshold of C$50,000/QALY. At a WTP threshold of C$100,000/QALY, apixaban had a higher probability of being cost-effective than PGx-based warfarin (54.6% versus 22.6%). CONCLUSION: We found that PGx-based warfarin for patients with AF is cost-effective at a WTP threshold of C$50,000/QALY. Apixaban had a higher probability of being cost-effective (> 50%) at a WTP threshold of C$93,000/QALY.

Does prescribing apixaban or rivaroxaban versus warfarin for patients diagnosed with atrial fibrillation save health system costs? A multivalued treatment effects analysis.

BACKGROUND: Non-valvular atrial fibrillation (AF) is a common heart arrhythmia in the elderly population. AF patients are at high-risk of ischemic strokes, but oral anticoagulant (OAC) therapy reduces such risks. Warfarin had been the standard OAC for AF patients, however its effectiveness is highly variable and dependent on close monitoring of the anticoagulant response. Newer OACs such as rivaroxaban and apixaban address these drawbacks but are more costly. It is uncertain which OAC therapy for AF is cost-saving from the healthcare system perspective. METHODS: We followed a cohort of patients in Ontario, Canada, aged ≥ 66 who were newly diagnosed with AF and prescribed OACs between 2012 and 2017. We used a two-stage estimation procedure. First, we account for the patient selection into OACs using a multinomial logit regression model and estimated propensity scores. Second, we used an inverse probability weighted regression adjustment approach to determine cost-saving OAC options. We also examined component-specific costs (i.e., drug, hospitalization, emergency department and physician) to understand the drivers of cost-saving OACs. RESULTS: We found that compared to warfarin, rivaroxaban and apixaban treatments were cost-saving options, with per-patient 1-year healthcare cost savings at $2436 and $1764, respectively. These savings were driven by cost-savings in hospitalization, emergency department visits, and physician visits, outweighing higher drug costs. These results were robust to alternative model specifications and estimation procedures. CONCLUSIONS: Treating AF patients with rivaroxaban and apixaban than warfarin reduces healthcare costs. OAC reimbursement policies for AF patients should consider rivaroxaban or apixaban over warfarin as the first-line treatment.

Differential effects of OATP2B1 on statin accumulation and toxicity in a beta cell model.

An increased risk of new-onset diabetes mellitus has been recently reported for statin therapy, and experimental studies have shown reduced glucose-stimulated insulin secretion (GSIS) and mitochondrial dysfunction in beta cells with effects differing among agents. Organic anion transporting polypeptide (OATP) 2B1 contributes to hepatic uptake of rosuvastatin, atorvastatin and pravastatin, three known substrates. Since OATP2B1 is present in beta cells of the human pancreas, we investigated if OATP2B1 facilitates the local accumulation of statins in a rat beta cell model INS-1 832/13 (INS-1) thereby amplifying statin-induced toxicity. OATP2B1 overexpression in INS-1 cells via adenoviral transduction showed 2.5-, 1.8- and 1.4-fold higher cellular retention of rosuvastatin, atorvastatin and pravastatin, respectively, relative to LacZ control, while absolute intracellular concentration was about twice as high for the lipophilic atorvastatin compared to the more hydrophilic rosuvastatin and pravastatin. After 24 h statin treatment at high concentrations, OATP2B1 enhanced statin toxicity involving activation of intrinsic apoptosis (caspase 3/7 activation) and mitochondrial dysfunction (NADH dehydrogenase activity) following rosuvastatin and atorvastatin, which was partly reversed by isoprenoids. OATP2B1 had no effect on statin-induced reduction in GSIS, mitochondrial electron transport chain complex expression or caspase 9 activation. We confirmed a dose-dependent reduction in insulin secretion by rosuvastatin and atorvastatin in native INS-1 with a modest change in cellular ATP. Collectively, our results indicate a role of OATP2B1, which is abundant in human beta cells, in statin accumulation and statin-induced toxicity but not insulin secretion of rosuvastatin and atorvastatin in INS-1 cells.

Thiopurine Methyltransferase Intermediate Metabolizer Status and Thiopurine-Associated Toxicity During Maintenance Therapy in Childhood Acute Lymphoblastic Leukemia.

Mercaptopurine is a cornerstone of maintenance chemotherapy in childhood acute lymphoblastic leukemia (ALL). Its cytotoxic effects are mediated by 6-thioguanine nucleotides (TGNs) incorporation into lymphocyte DNA. Thiopurine methyltransferase (TPMT) inactivates mercaptopurine, and deficiency resulting from genetic variants increases TGN exposure and hematopoietic toxicity. Although mercaptopurine-dose reduction reduces toxicity risk without compromising relapse rate in patients with TPMT deficiency, dosing recommendations for those with moderately reduced activity (intermediate metabolizer (IM)) are less clear and their clinical impacts have yet to be established. This cohort study assessed the effect of TPMT IM status on mercaptopurine-associated toxicity and TGN blood exposure in pediatric patients with ALL initiated on standard dose mercaptopurine. Of 88 patients studied (mean age 4.8 years), 10 (11.4%) were TPMT IM, and all had undergone ≥ 3 cycles of maintenance therapy (80% completed). A larger proportion of TPMT IM than normal metabolizers (NM) had febrile neutropenia (FN) during the first two cycles of maintenance, reaching significance in the second cycle (57% vs. 15%, respectively; odds ratio = 7.33, P < 0.05). Compared to NM, FN events occurred more frequently and with prolonged duration in IM in cycles 1 and 2 (adjusted P < 0.05). IM had a 2.46-fold increased hazard ratio for FN, and about twofold higher TGN level than NM (P < 0.05). Myelotoxicity was more common in IM than NM (86% vs. 42%, respectively) during cycle 2 (odds ratio = 8.2, P < 0.05). TPMT IM initiated at a standard mercaptopurine dose are at greater risk for FN during early cycles of maintenance therapy, thus our findings support genotype-guided dose adjustment to reduce toxicity.

DPYD Exon 4 Deletion Associated with Fluoropyrimidine Toxicity and Importance of Copy Number Variation.

Fluoropyrimidine chemotherapy is associated with interpatient variability in toxicity. A major contributor to unpredictable and severe toxicity relates to single nucleotide variation (SNV) in dihydropyrimidine dehydrogenase (DPYD), the rate-limiting fluoropyrimidine metabolizing enzyme. In addition to SNVs, a study of Finnish patients suggested that a DPYD exon 4 deletion was observed in their population. To better understand the potential generalizability of such findings, we investigated the presence of this exon 4 deletion in our Canadian patient population, using a TaqMan assay. We selected 125 patients who experienced severe fluoropyrimidine-associated toxicity, and 125 matched controls. One patient in the severe toxicity group harbored a haploid DPYD exon 4 deletion, and required a 35% dose reduction after their first fluoropyrimidine treatment cycle due to toxicity and required an additional 30% dose reduction before tolerating treatment. The predicted allele frequency was 0.2% in our cohort, much lower than the 2.4% previously reported. We also carried out a literature review of copy number variation (CNV) in the DPYD gene, beyond fluoropyrimidine toxicity and show that various types of CNV in DPYD are present in the population. Taken together, our findings suggest that CNV in DPYD may be an underappreciated determinant of DPYD-mediated fluoropyrimidine toxicity.

Patient-specific genetic factors predict treatment failure in sofosbuvir-treated patients with chronic hepatitis C.

BACKGROUND & AIMS: According to pivotal clinical trials, cure rates for sofosbuvir-based antiviral therapy exceed 96%. Treatment failure is usually assumed to be because of virological resistance-associated substitutions or clinical risk factors, yet the role of patient-specific genetic factors has not been well explored. We determined if patient-specific genetic factors help predict patients likely to fail sofosbuvir treatment in real-world treatment situations. METHODS: We recruited sofosbuvir-treated patients with chronic hepatitis C from five Canadian treatment sites, and performed a case-control pharmacogenomics study assessing both previously published and novel genetic polymorphisms. Specifically studied were variants predicted to impair CES1-dependent production of sofosbuvir's active metabolite, interferon-λ signalling variants expected to impact a patient's immune response to the virus and an HLA variant associated with increased spontaneous and treatment-induced viral clearance. RESULTS: Three hundred and fifty-nine sofosbuvir-treated patients were available for analyses after exclusions, with 34 (9.5%) failing treatment. We identified CES1 variants as novel predictors for treatment failure in European patients (rs115629050 or rs4513095; odds ratio (OR): 5.43; 95% confidence interval (CI): 1.64-18.01; P = .0057), replicated associations with IFNL4 variants predicted to increase interferon-λ signalling (eg rs12979860; OR: 2.25; 95% CI: 1.25-4.06; P = .0071) and discovered a novel association with a coding variant predicted to enhance the activity of IFNL4's receptor (rs2834167 in IL10RB; OR: 1.81; 95% CI: 1.01-3.24; P = .047). CONCLUSIONS: Ultimately, this work demonstrates that patient-specific genetic factors could be used as a tool to identify patients at higher risk of treatment failure and allow for these patients to receive effective therapy sooner.

Association of Sex With Stroke and Bleeding Risk of Apixaban and Rivaroxaban in Elderly Atrial Fibrillation Patients Using Propensity Score Weights.

BACKGROUND: Evidence from clinical trials suggests a differential effect of sex on the effectiveness and safety of direct oral anticoagulants (DOACs) for stroke prophylaxis in atrial fibrillation (AF). METHODS: This population-based cohort study examined the independent effect of sex on hemorrhage and ischemic stroke in 23,884 patients (55% females; age ≥ 66 years) with AF starting apixaban or rivaroxaban treatment in Ontario, Canada. Patients were followed for 90 days after their DOAC prescription. Using female sex as the exposure of interest, differences in baseline characteristics were balanced between sexes using inverse probability weights based on propensity scores. Applying weighted modified Poisson regression, risk ratios (RRs) were estimated for major hemorrhage, ischemic stroke/systemic embolism/transient ischemic attack (hereafter stroke), myocardial infarction, and all-cause mortality, with males as a reference. RESULTS: Females were older, had higher predicted stroke risk (based on CHADS2 score), and had fewer comorbidities than did males. Males had a higher prevalence of coronary artery disease, diabetes, and cancer, and similar predicted bleeding risk (based on HAS-BLED score). After weighting, baseline characteristics were well balanced. The 90-day risks for hemorrhage (RR 0.96; 95% confidence interval [CI] 0.80-1.15; P = 0.69) and stroke (RR 1.01; 95% CI 0.86-1.19; P = 0.94) were similar between sexes, which remained true when assessing each DOAC separately by dosing regimen. Compared to males, females had a lower risk for myocardial infarction (RR 0.66; 95% CI 0.52-0.84; P = 0.0008), and for all-cause mortality (RR 0.76; 95% CI 0.67-0.87; P < 0.0001). CONCLUSIONS: Our findings do not suggest an association of sex with the 90-day risk of hemorrhage or ischemic stroke in older AF patients prescribed apixaban or rivaroxaban.

CONTEXTE: Les données probantes issues des essais cliniques donnent à penser que l'efficacité et l'innocuité des anticoagulants oraux directs (AOD) utilisés pour la prophylaxie des accidents vasculaires cérébraux (AVC) dans un contexte de fibrillation auriculaire (FA) varient selon le sexe du patient. MÉTHODOLOGIE: Cette étude de cohorte populationnelle a examiné l'effet indépendant du sexe sur l'hémorragie et l'AVC ischémique chez 23 884 patients (55 % de femmes; âge ≥ 66 ans) atteints de FA ayant amorcé un traitement par l'apixaban ou le rivaroxaban en Ontario (Canada). Les patients ont été suivis pendant 90 jours après avoir reçu une ordonnance d'AOD. Le sexe féminin constituant l'exposition d'intérêt, les différences quant aux caractéristiques initiales ont été réparties de façon équilibrée entre les sexes au moyen d'une pondération par probabilité inverse reposant sur le score de propension. La régression de Poisson modifiée avec pondération a servi à estimer les rapports de risques (RR) d'hémorragie majeure, d'AVC ischémique/d'embolie systémique/d'accident ischémique transitoire (ci-après AVC), d'infarctus du myocarde et de mortalité toutes causes confondues, les hommes formant la population de référence. RÉSULTATS: Les femmes étaient plus âgées, présentaient un risque prévu d'AVC plus élevé (d'après le score CHADS2) et présentaient moins de maladies concomitantes que les hommes. Les hommes présentaient une prévalence plus élevée de coronaropathie, de diabète et de cancer, et un risque prévu d'hémorragie similaire (compte tenu du score HAS-BLED). Après la pondération, la répartition des caractéristiques initiales des patients était bien équilibrée. Le risque d'hémorragie (RR : 0,96; intervalle de confiance [IC] à 95 % : 0,80-1,15; P = 0,69) et d'AVC (RR : 1,01; IC à 95 % : 0,86-1,19; P = 0,94) sur 90 jours était similaire pour les deux sexes, et il en était de même lorsque chaque AOD a été évalué séparément en fonction du schéma posologique. Par rapport aux hommes, les femmes présentaient un risque plus faible d'infarctus du myocarde (RR : 0,66; IC à 95 % : 0,52-0,84; P = 0,0008) et de mortalité toutes causes confondues (RR : 0,76; IC à 95 % : 0,67-0,87; P < 0,0001). CONCLUSIONS: Nos résultats ne laissent présumer aucune association entre le sexe et le risque d'hémorragie ou d'AVC ischémique sur une période de 90 jours chez les patients âgés atteints de FA à qui l'apixaban ou le rivaroxaban sont prescrits.

In-vitro characterization of coding variants with predicted functional implications in the efflux transporter multidrug resistance protein 4 (MRP4, ABCC4).

MRP4 (gene ABCC4) is a polymorphic efflux transporter that has been implicated in drug-induced toxicity. We selected ten commonly observed MRP4 coding variants among Europeans for experimental characterization including nine variants predicted to be deleterious or functional (combined annotation-dependent depletion score >15). We assessed protein localization and activity by quantifying intracellular accumulation of two prototypic substrates, taurocholic acid (TCA) and estradiol 17-ß-glucuronide (E217ßG), in HEK293T over-expressing MRP4 wildtype or variant where cellular substrate loading was optimized through co-transfection with an uptake transporter. V458M, a novel variant not previously studied, and T1142M, showed reduced activity compared to MRP4 wildtype for E217ßG and TCA (P < 0.01), while L18I, G187W, K293E, and R531Q moderately increased activity in a substrate-dependent manner. Protein expression analysis indicated reduced cell surface expression for V458M (P < 0.01) but not T1142M compared to wildtype. Reduced activity may result from altered surface expression (V458M) or intrinsic activity as both variants map within the nucleotide-binding domains of MRP4. G187W showed a trend for reduced surface expression (P = 0.054) despite transport comparable or increased to wildtype suggesting enhanced intrinsic activity. Our findings suggest moderately altered MRP4 activity in six out of nine predicted functional variants with likely different mechanisms and substrate-specific effects. Cell-based studies using multiple known substrates are warranted to more accurately predict functional variants in this clinically important transporter.

Organic Anion Transporting Polypeptide 2B1 (OATP2B1) Genetic Variants: In Vitro Functional Characterization and Association With Circulating Concentrations of Endogenous Substrates.

Organic anion transporting polypeptide 2B1 (OATP2B1, gene SLCO2B1) is an uptake transporter that is thought to determine drug disposition and in particular, the oral absorption of medications. At present, the clinical relevance of SLCO2B1 genetic variation on pharmacokinetics is poorly understood. We sought to determine the functional activity of 5 of the most common missense OATP2B1 variants (c.76_84del, c.601G>A, c.917G>A, c.935G>A, and c.1457C>T) and a predicted dysfunctional variant (c.332G>A) in vitro. Furthermore, we measured the basal plasma concentrations of endogenous OATP2B1 substrates, namely estrone sulfate, dehydroepiandrosterone sulfate (DHEAS), pregnenolone sulfate, coproporphyrin I (CPI), and CPIII, and assessed their relationships with SLCO2B1 genotypes in 93 healthy participants. Compared to reference OATP2B1, the transport activities of the c.332G>A, c.601G>A and c.1457C>T variants were reduced among the substrates examined (estrone sulfate, DHEAS, CPI, CPIII and rosuvastatin), although there were substrate-dependent effects. Lower transport function of OATP2B1 variants could be explained by diminished cell surface expression. Other OATP2B1 variants (c.76-84del, c.917G>A and c.935G>A) had similar activity to the reference transporter. In the clinical cohort, the SLCO2B1 c.935G>A allele was associated with both higher plasma CPI (42%) and CPIII (31%) concentrations, while SLCO2B1 c.917G>A was linked to lower plasma CPIII by 28% after accounting for the effects of age, sex, and SLCO1B1 genotypes. No association was observed between SLCO2B1 variant alleles and estrone sulfate or DHEAS plasma concentrations, however 45% higher plasma pregnenolone sulfate level was associated with SLCO2B1 c.1457C>T. Taken together, we found that the impacts of OATP2B1 variants on transport activities in vitro were not fully aligned with their associations to plasma concentrations of endogenous substrates in vivo. Additional studies are required to determine whether circulating endogenous substrates reflect OATP2B1 activity.

Novel variant in glycophorin c gene protects against ribavirin-induced anemia during chronic hepatitis C treatment.

BACKGROUND: The current use of ribavirin in difficult-to-cure chronic hepatitis C patients (HCV) and patients with severe respiratory infections is constrained by the issue of ribavirin-induced hemolytic anemia that affects 30% of treated patients, requiring dosage modification or discontinuation. Though some genetic variants have been identified predicting this adverse effect, known clinical and genetic factors do not entirely explain the risk of ribavirin-induced anemia. METHODS: We assessed the associations of previously identified variants in inosine triphosphatase (ITPA), solute carrier 28A2 (SLC28A2) and vitamin D receptor (VDR) genes with ribavirin-induced anemia defined as hemoglobin decline of ≥30 g/L on treatment, followed by a staged discovery (n = 114), replication (n = 74), and combined (n = 188) genome-wide association study to uncover potential new predictive variants. RESULTS: We identified a novel association in the gene coding glycophorin C (rs6741425; OR:0.12, 95%CI:0.04-0.34, P = 2.94 × 10-6) that predicts protection against ribavirin-induced anemia. We also replicated the associations of ITPA and VDR genetic variants with the development of ribavirin-induced anemia (rs1127354; OR:0.13, 95%CI:0.04-0.41, P = 8.66 ×10-5; and rs1544410; OR:1.65, 95%CI:1.01-2.70, P = 0.0437). CONCLUSIONS: GYPC variation affecting erythrocyte membrane strength is important in predicting risk for developing ribavirin-induced anemia. ITPA and VDR genetic variants are also important predictors of this adverse reaction.

Impact of pretreatment dihydropyrimidine dehydrogenase genotype-guided fluoropyrimidine dosing on chemotherapy associated adverse events.

Consensus guidelines exist for genotype-guided fluoropyrimidine dosing based on variation in the gene dihydropyrimidine dehydrogenase (DPYD). However, these guidelines have not been widely implemented in North America and most studies of pretreatment DPYD screening have been conducted in Europe. Given regional differences in treatment practices and rates of adverse events (AEs), we investigated the impact of pretreatment DPYD genotyping on AEs in a Canadian context. Patients referred for DPYD genotyping prior to fluoropyrimidine treatment were enrolled from December 2013 through November 2019 and followed until completion of fluoropyrimidine treatment. Patients were genotyped for DPYD c.1905+1G>A, c.2846A>T, c.1679T>G, and c.1236G>A. Genotype-guided dosing recommendations were informed by Clinical Pharmacogenetics Implementation Consortium guidelines. The primary outcome was the proportion of patients who experienced a severe fluoropyrimidine-related AE (grade ≥3, Common Terminology Criteria for Adverse Events version 5.0). Secondary outcomes included early severe AEs, severe AEs by toxicity category, discontinuation of fluoropyrimidine treatment due to AEs, and fluoropyrimidine-related death. Among 1394 patients, mean (SD) age was 64 (12) years, 764 (54.8%) were men, and 47 (3.4%) were DPYD variant carriers treated with dose reduction. Eleven variant carriers (23%) and 418 (31.0%) noncarriers experienced a severe fluoropyrimidine-related AE (p = 0.265). Six carriers (15%) and 284 noncarriers (21.1%) experienced early severe fluoropyrimidine-related AEs (p = 0.167). DPYD variant carriers treated with genotype-guided dosing did not experience an increased risk for severe AEs. Our data support a role for DPYD genotyping in the use of fluoropyrimidines in North America.

Genetic variation in the farnesoid X-receptor predicts Crohn's disease severity in female patients.

The farnesoid X receptor (FXR) is implicated in Crohn's disease (CD) pathogenesis. It is unclear how genetic variation in FXR impacts CD severity versus genetic variation in nuclear receptors such as pregnane X receptor (PXR) and the multi-drug resistance protein 1 (MDR1, ABCB1). To evaluate FXR-1G > T as a genomic biomarker of severity in CD and propose a plausible molecular mechanism. A retrospective study (n = 542) was conducted in a Canadian cohort of CD patients. Genotypic analysis (FXR-1G > T, MDR1 3435C > T and PXR -25385C > T) as well as determination of the FXR downstream product, fibroblast growth factor (FGF) 19 was performed. Primary outcomes included risk and time to first CD-related surgery. The effect of estrogen on wild type and variant FXR activity was assessed in HepG2 cells. The FXR-1GT genotype was associated with the risk of (odds ratio, OR = 3.34, 95% CI = 1.58-7.05, p = 0.002) and earlier progression to surgery (hazard ratio, HR = 3.00, 95% CI = 1.86-4.83, p < 0.0001) in CD. Female carriers of the FXR-1GT genotype had the greatest risk of surgery (OR = 14.87 95% CI = 4.22-52.38, p < 0.0001) and early progression to surgery (HR = 6.28, 95% CI = 3.62-10.90, p < 0.0001). Women carriers of FXR-1GT polymorphism had a three-fold lower FGF19 plasma concentration versus women with FXR-1GG genotype (p < 0.0001). In HepG2 cells cotransfected with estrogen receptor (ER) and FXR, presence of estradiol further attenuated variant FXR activity. MDR1 and PXR genotypes were not associated with surgical risk. Unlike MDR1 and PXR, FXR-1GT genetic variation is associated with earlier and more frequent surgery in women with CD. This may be through ER-mediated attenuation of FXR activation.

Variant discovery using next-generation sequencing and its future role in pharmacogenetics.

Next-generation sequencing (NGS) has enabled the discovery of a multitude of novel and mostly rare variants in pharmacogenes that may alter a patient's therapeutic response to drugs. In addition to single nucleotide variants, structural variation affecting the number of copies of whole genes or parts of genes can be detected. While current guidelines concerning clinical implementation mostly act upon well-documented, common single nucleotide variants to guide dosing or drug selection, in silico and large-scale functional assessment of rare variant effects on protein function are at the forefront of pharmacogenetic research to facilitate their clinical integration. Here, we discuss the role of NGS in variant discovery, paving the way for more comprehensive genotype-guided pharmacotherapy that can translate to improved clinical care.

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.

Targeted next generation sequencing as a tool for precision medicine.

BACKGROUND: Targeted next-generation sequencing (NGS) enables rapid identification of common and rare genetic variation. The detection of variants contributing to therapeutic drug response or adverse effects is essential for implementation of individualized pharmacotherapy. Successful application of short-read based NGS to pharmacogenes with high sequence homology, nearby pseudogenes and complex structure has been previously shown despite anticipated technical challenges. However, little is known regarding the utility of such panels to detect copy number variation (CNV) in the highly polymorphic cytochrome P450 (CYP) 2D6 gene, or to identify the promoter (TA)7 TAA repeat polymorphism UDP glucuronosyltransferase (UGT) 1A1*28. Here we developed and validated PGxSeq, a targeted exome panel for pharmacogenes pertinent to drug disposition and/or response. METHODS: A panel of capture probes was generated to assess 422 kb of total coding region in 100 pharmacogenes. NGS was carried out in 235 subjects, and sequencing performance and accuracy of variant discovery validated in clinically relevant pharmacogenes. CYP2D6 CNV was determined using the bioinformatics tool CNV caller (VarSeq). Identified SNVs were assessed in terms of population allele frequency and predicted functional effects through in silico algorithms. RESULTS: Adequate performance of the PGxSeq panel was demonstrated with a depth-of-coverage (DOC) ≥ 20× for at least 94% of the target sequence. We showed accurate detection of 39 clinically relevant gene variants compared to standard genotyping techniques (99.9% concordance), including CYP2D6 CNV and UGT1A1*28. Allele frequency of rare or novel variants and predicted function in 235 subjects mirrored findings from large genomic datasets. A large proportion of patients (78%, 183 out of 235) were identified as homozygous carriers of at least one variant necessitating altered pharmacotherapy. CONCLUSIONS: PGxSeq can serve as a comprehensive, rapid, and reliable approach for the detection of common and novel SNVs in pharmacogenes benefiting the emerging field of precision medicine.

Apixaban Concentrations with Lower than Recommended Dosing in Older Adults with Atrial Fibrillation.

OBJECTIVES: Lower than recommended doses of direct-acting oral anticoagulants are often prescribed to older adults with nonvalvular atrial fibrillation (NVAF). Our goal was to determine the consequences of lower than recommended dosing on plasma apixaban concentrations during the clinical care of older adults with NVAF. DESIGN: Convenience sample of patients receiving anticoagulation during 2017. SETTING: Academic medical center. PARTICIPANTS: Stable adults older than 65 years with NVAF receiving apixaban on a chronic basis. MEASUREMENTS: Patient age, weight, creatinine, co-medications, and apixaban concentrations. RESULTS: A total of 110 older adults with NVAF (mean age = 80.4 y; range = 66-100 y with 45% women) were studied. Overall, 48 patients received recommended dosing of 5 mg twice/day, and 42 received lower than recommended dosing. One patient in each category had concentrations below the expected 5% to 95% range at time of peak concentrations. Differences in proportion of apixaban concentrations within or outside expected ranges were not significant between patients receiving lower than recommended doses and those dosed as recommended at 5 mg twice/day (P = .35). However, in patients dosed as recommended with 5 mg twice/day, four had concentrations above the 5% to 95% range for peak levels expected at 3 to 4 hours after dosing; in two, this occurred around the midpoint of the dosing interval. Twenty patients received 2.5 mg twice/day as recommended. One-third had apixaban concentrations higher than expected peak concentrations compared with the clinical trials, and more than two-thirds had levels above the reported median for peak concentrations. CONCLUSIONS: Apixaban concentrations in older adults with NVAF seen clinically were higher than expected based on clinical trial data. The findings raise questions about the optimal dosing of apixaban in older adults with NVAF encountered outside of clinical trials and suggest a role for the monitoring of apixaban concentrations during care of patients that differ from those in randomized trials or when considering dosing outside of published guidelines. J Am Geriatr Soc 67:1902-1906, 2019.

Fexofenadine and Rosuvastatin Pharmacokinetics in Mice with Targeted Disruption of Organic Anion Transporting Polypeptide 2B1.

Organic anion transporting polypeptide 2B1 (OATP2B1) is a widely expressed membrane transporter with diverse substrate specificity. In vitro and clinical studies suggest a role for intestinal OATP2B1 in the oral absorption of medications. Moreover, OATP2B1 is highly expressed in hepatocytes where it is thought to promote liver drug clearance. However, until now, a shortcoming of studies implicating OATP2B1 in drug disposition has been a lack of in vivo models. Here, we report the development of a knockout (KO) mouse model with targeted, global disruption of the Slco2b1 gene to examine the disposition of two confirmed mOATP2B1 substrates, namely, fexofenadine and rosuvastatin. The plasma pharmacokinetics of intravenously administered fexofenadine was not different between KO and wild-type (WT) mice. However, after oral fexofenadine administration, KO mice had 70% and 41% lower maximal plasma concentration (C max) and area under the plasma concentration-time curve (AUC0-last) than WT mice, respectively. In WT mice, coadministration of fexofenadine with grapefruit juice (GFJ) or apple juice (AJ) was associated with reduced C max by 80% and 88%, respectively, while the AUC0-last values were lower by 35% and 70%, respectively. In KO mice, AJ coadministration reduced oral fexofenadine C max and AUC0-last values by 67% and 59%, respectively, while GFJ had no effects. Intravenous and oral rosuvastatin pharmacokinetics were similar among WT and KO mice. We conclude that intestinal OATP2B1 is a determinant of oral fexofenadine absorption, as well as a target for fruit juice interactions. OATP2B1 does not significantly influence rosuvastatin disposition in mice. SIGNIFICANCE STATEMENT: A novel mouse model with targeted disruption of the Slco2b1 gene revealed that OATP2B1 is a determinant of oral absorption but not systemic disposition of fexofenadine, as well as a target of fruit juice interactions. Rosuvastatin oral and intravenous pharmacokinetics were not dependent on OATP2B1. These findings support the utility of the Slco2b1 KO mouse model for defining mechanisms of drug disposition at the intersection of in vitro and clinical pharmacology.

Differences in Warfarin Pharmacodynamics and Predictors of Response Among Three Racial Populations.

BACKGROUND: Population differences in warfarin dosing requirement have been reported; however, unlike the pharmacokinetics (PK) of warfarin, the quantitative influences of pharmacodynamic (PD) factors on the anticoagulation response to warfarin in different ethnic populations are totally unknown. METHODS: Using population PK/PD analysis, we attempted to identify predictors of S-warfarin clearance [CL(S)] and half maximal effective concentration (EC50) to quantify racial differences in both PK and PD parameters, and to assess the contribution of these parameters to the international normalized ratio (INR) and over-anticoagulation response (INR ≥ 4) in a cohort of 309 White, Asian and African American patients. RESULTS: Similar to our previous findings, the median CL(S) was 30% lower in African American patients than Asian and White patients (169 vs. 243 and 234 mL/h, p < 0.01). EC50 showed a greater racial difference than CL(S) [1.03, 1.70 and 2.76 µg/mL for Asian, White and African American patients, respectively, p < 0.01). Significant predictors of INR included demographic/clinical (age, body weight, creatinine clearance and sex) and genotypic (CYP2C9*3,*8 and VKORC1 -1639G>A) factors, as well as African American ethnicity. In all three racial groups, genetic predictors of INR appeared to have greater influence than demographic/clinical predictors. Both CL(S) and EC50 contributed to the over-anticoagulation response to warfarin. Patients having VKORC1 -1639 G>A and/or factors associated with reduced CYP2C9 activity were more likely to have an INR ≥ 4. CONCLUSIONS: Although there were contrasting racial differences in CL(S) and EC50 that impacted on the INR, the racial difference in EC50 was greater than that for CL(S), thus explaining the higher warfarin requirement for African American patients.

The Role of Next-Generation Sequencing in Pharmacogenetics and Pharmacogenomics.

Inherited genetic variations in pharmacogenetic loci are widely acknowledged as important determinants of phenotypic differences in drug response, and may be actionable in the clinic. However, recent studies suggest that a considerable number of novel rare variants in pharmacogenes likely contribute to a still unexplained fraction of the observed interindividual variability. Next-generation sequencing (NGS) represents a rapid, relatively inexpensive, large-scale DNA sequencing technology with potential relevance as a comprehensive pharmacogenetic genotyping platform to identify genetic variation related to drug therapy. However, many obstacles remain before the clinical use of NGS-based test results, including technical challenges, functional interpretation, and strict requirements for diagnostic tests. Advanced computational analyses, high-throughput screening methodologies, and generation of shared resources with cell-based and clinical information will facilitate the integration of NGS data into candidate genotyping approaches, likely enhancing future drug phenotype predictions in patients.