Study on genotype and phenotype of novel CYP2D6 variants using pharmacokinetic and pharmacodynamic models with metoprolol as a substrate drug.

To investigate the pharmacokinetic and pharmacodynamic profiles of volunteers carrying CYP2D6 genotypes with unknow metabolic phenotypes, a total of 22 volunteers were recruited based on the sequencing results. Peripheral blood and urine samples were collected at specific time points after oral administration of metoprolol. A validated high-performance liquid chromatography (HPLC) method was used to determine the concentrations of metoprolol and α-hydroxymetoprolol. Blood pressure and electrocardiogram were also monitored. The results showed that the main pharmacokinetic parameters of metoprolol in CYP2D6*1/*34 carriers are similar to those in CYP2D6*1/*1 carriers. However, in individuals carrying the CYP2D6*10/*87, CYP2D6*10/*95, and CYP2D6*97/*97 genotypes, the area under the curve (AUC) and half-life (t1/2) of metoprolol increased by 2-3 times compared to wild type. The urinary metabolic ratio of metoprolol in these genotypes is consistent with the trends observed in plasma samples. Therefore, CYP2D6*1/*34 can be considered as normal metabolizers, while CYP2D6*10/*87, CYP2D6*10/*95, and CYP2D6*97/*97 are intermediate metabolizers. Although the blood concentration of metoprolol has been found to correlate with CYP2D6 genotype, its blood pressure-lowering effect reaches maximum effectiveness at a reduction of 25 mmHg. Furthermore, P-Q interval prolongation and heart rate reduction are not positively correlated with metoprolol blood exposure. Based on the pharmacokinetic-pharmacodynamic model, this study clarified the properties of metoprolol in subjects with novel CYP2D6 genotypes and provided important fundamental data for the translational medicine of this substrate drug.

Mechanism-Based Inactivation of CYP2D6 by Phellopterin and Related Drug-Drug Interaction with Metoprolol.

Phellopterin (PLP) is a linear furanocoumarin widely found in citrus fruits and herbal medicines. The study aims to comprehensively investigate the mechanism of inhibition of CYP2D6 enzyme activity by PLP and its alteration of metoprolol pharmacokinetics. PLP was found to irreversibly inhibit CYP2D6 in time-, concentration-, and nicotinamide adenine dinucleotide phosphate-dependent manners. Coincubation with quinidine, which is a competitive inhibitor of CYP2D6, attenuated this time-dependent inhibition. Glutathione (GSH) and catalase/superoxide dismutase failed to reverse the PLP-induced CYP2D6 inactivation. GSH trapping experiments provided strong evidence that PLP metabolic activation produces epoxide or γ-ketoaldehyde intermediates. In addition, pretreatment with PLP resulted in significant increases in Cmax and area under curve of plasma metoprolol in rats.

Pharmacogenomic markers of metoprolol and α-OH-metoprolol concentrations: a genome-wide association study.

Aim: Few genome-wide association studies (GWASs) have been conducted to identify predictors of drug concentrations. The authors therefore sought to discover the pharmacogenomic markers involved in metoprolol pharmacokinetics. Patients & methods: The authors performed a GWAS of a cross-sectional study of 993 patients from the Montreal Heart Institute Biobank taking metoprolol. Results: A total of 391 and 444 SNPs reached the significance threshold of 5 × 10-8 for metoprolol and α-OH-metoprolol concentrations, respectively. All were located on chromosome 22 at or near the CYP2D6 gene, encoding CYP450 2D6, metoprolol's main metabolizing enzyme. Conclusion: The results reinforce previous findings of the importance of the CYP2D6 locus for metoprolol concentrations and confirm that large biobanks can be used to identify genetic determinants of drug pharmacokinetics at a GWAS significance level.

Physiologically based pharmacokinetic modelling to predict the pharmacokinetics of metoprolol in different CYP2D6 genotypes.

Metoprolol, a selective ß1-adrenoreceptor blocking agent used in the treatment of hypertension, angina, and heart failure, is primarily metabolized by the CYP2D6 enzyme, which catalyzes α-hydroxylation and O-desmethylation. As CYP2D6 is genetically highly polymorphic and the enzymatic activity differs greatly depending on the presence of the mutant allele(s), the pharmacokinetic profile of metoprolol is highly variable depending on the genotype of CYP2D6. The aim of study was to develop the physiologically based pharmacokinetic (PBPK) model of metoprolol related to CYP2D6 genetic polymorphism for personalized therapy with metoprolol. For PBPK modelling, our previous pharmacogenomic data were used. To obtain kinetic parameters (Km, Vmax, and CLint) of each genotype, the recombinant CYP enzyme of each genotype was incubated with metoprolol and metabolic rates were assayed. Based on these data, the PBPK model of metoprolol was developed and validated in different CYP2D6 genotypes using PK-Sim® software. As a result, the input values for various parameters for the PBPK model were presented and the PBPK model successfully described the pharmacokinetics of metoprolol in each genotype group. The simulated values were within the acceptance criterion (99.998% confidence intervals) compared with observed values. The PBPK model developed in this study can be used for personalized pharmacotherapy with metoprolol in individuals of various races, ages, and CYP2D6 genotypes.

Clinical Pharmacokinetics of Metoprolol: A Systematic Review.

BACKGROUND: Metoprolol is recommended for therapeutic use in multiple cardiovascular conditions, thyroid crisis, and circumscribed choroidal hemangioma. A detailed systematic review on the metoprolol literature would be beneficial to assess all pharmacokinetic parameters in humans and their respective effects on patients with hepatic, renal, and cardiovascular diseases. This review combines all the pharmacokinetic data on metoprolol from various accessible studies, which may assist in clinical decision making. METHODOLOGY: The Google Scholar and PubMed databases were searched to screen articles associated with the clinical pharmacokinetics of metoprolol. The comprehensive literature search retrieved 41 articles including data on plasma concentration-time profiles after intravenous and oral (immediate-release, controlled-release, slow-release, or extended-release) routes of administration, and at least one pharmacokinetic parameter was reported in all studies included. RESULTS: Out of 41 retrieved articles, six were after intravenous and 12 were after oral administration in healthy individuals. The oral studies depict a dose-dependent increase in maximum plasma concentration (Cmax), time to reach maximum plasma concentration (Tmax), and area under the concentration-time curve (AUC). Two studies were conducted in R- and S-enantiomers, in which one study reported the gender differences, depicting greater Cmax and AUC among women, whereas in another study S-metoprolol was found to have higher values of Cmax, Tmax, and AUC in comparison with R-metoprolol. Results in different diseases depicted that after IV administration of 20 mg, patients with renal impairment showed an increase in clearance (CL) (60 L/h vs 48 L/h) compared with healthy subjects, whereas a decrease in CL (36.6 ± 7.8 L/h vs 48 ± 6.6 L/h) was seen in patients with hepatic cirrhosis at a similar dose. In comparison with a single oral dose following administration of 15 mg IV in three divided doses, patients having an acute myocardial infarction (AMI) showed an increase in Cmax (823 nmol/L vs 248 nmol/L) at a steady state. Twenty different studies have reported significant changes in CL, Cmax, and AUC of metoprolol when it is co-administered with other drugs. One study has reported a drug-food interaction for metoprolol but no significant changes were seen in the Cmax and AUC. CONCLUSION: This review summarizes all the pharmacokinetic parameters of metoprolol after pooling up-to-date data from all the studies available. The summarized pharmacokinetic data presented in this review can assist in developing and evaluating pharmacokinetic models of metoprolol. Moreover, this data can provide practitioners with an insight into dosage adjustments among the diseased populations and can assist in preventing potential adverse drug reactions. This review can also help avoid side effects and drug-drug interactions.

Inhibitory effects of fluoxetine and duloxetine on the pharmacokinetics of metoprolol in vivo and in vitro.

Depression is common among people with cardiovascular diseases. Therefore, the combined use of antidepressants and cardiovascular drugs is very common, which increases the possibility of drug interaction. Simultaneously compare the effects of duloxetine and fluoxetine on metoprolol metabolism, and provide evidence-based guidance for medication safety. Sprague-Dawley rats were randomly divided into three groups: group A (10.3 mg/kg metoprolol alone), group B (10.3 mg/kg metoprolol + 6.2 mg/kg fluoxetine), and group C (10.3 mg/kg metoprolol + 6.2 mg/kg duloxetine). Tail vein blood was collected and subjected to the ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) detection. Moreover, in vitro inhibition of fluoxetine and duloxetine were assessed by incubating liver microsomes and CYP2D6.1 with metoprolol. In in vivo study, the administration of fluoxetine or duloxetine significantly increased the AUC(0-𝑡) and AUC(0-∞) of metoprolol (P < 0.05). Differences between fluoxetine and duloxetine in plasma concentration were also investigated, and their pharmacokinetic parameters such as AUC(0-𝑡) and AUC(0-∞) were significantly distinct (P < 0.05). In vitro, fluoxetine and duloxetine inhibited the metabolism of metoprolol via mixed competitive mechanism of cytochrome P450. IC50 values of fluoxetine and duloxetine were 12.86 and 2.51 µM, respectively. Moreover, the metabolism rate of metoprolol was inhibited to 19.62% and 17.14% in recombinant human CYP2D6.1 by fluoxetine and duloxetine, respectively. Duloxetine showed a more significant inhibitory potential compared to fluoxetine in vitro, but the main pharmacokinetic parameters of fluoxetine and duloxetine revealed differences in inhibiting metoprolol metabolism in vivo.

A randomized, cross-over trial of metoprolol succinate formulations to evaluate PK and PD end points for therapeutic equivalence.

There are limited comparison data throughout the dosing interval for generic versus brand metoprolol extended-release (ER) tablets. We compared the pharmacokinetics (PKs) and pharmacodynamics of brand name versus two generic formulations (drugs 1 and 2) of metoprolol ER tablets with different time to maximum concentration (Tmax ) in adults with hypertension. Participants were randomized to equal drug doses (50-150 mg/day) administered in one of two sequences (brand-drug1-brand-drug2 or brand-drug2-brand-drug1) and completed 24-h PK, digital heart rate (HR), ambulatory blood pressure (BP), and HR studies after taking each formulation for greater than or equal to 7 days. Metoprolol concentrations were determined by liquid chromatography tandem mass spectrometry, with noncompartmental analysis performed to obtain PK parameters in Phoenix WinNonlin. Heart rate variability (HRV) low-to-high frequency ratio was determined per quartile over the 24-h period. Thirty-six participants completed studies with the brand name and at least one generic product. Among 30 participants on the 50 mg dose, the primary PK end points of area under the concentration-time curve and Cmax were similar between products; Tmax was 6.1 ± 3.6 for the brand versus 3.5 ± 4.9 for drug 1 (p = 0.019) and 9.6 ± 3.2 for drug 2 (p < 0.001). Among all 36 participants, 24-h BPs and HRs were similar between products. Mean 24-h HRV low-to-high ratio was also similar for drug 1 (2.04 ± 1.35), drug 2 (1.86 ± 1.35), and brand (2.04 ± 1.77), but was more sustained over time for the brand versus drug 1 (drug × quartile interaction p = 0.017). Differences in Tmax between metoprolol ER products following repeated doses may have implications for drug effects on autonomic balance over the dosing interval.

Leveraging large observational studies to discover genetic determinants of drug concentrations: A proof-of-concept study.

Large, observational genetic studies are commonly used to identify genetic factors associated with diseases and disease-related traits. Such cohorts have not been commonly used to identify genetic predictors of drug dosing or concentrations, perhaps because of the heterogeneity in drug dosing and formulation, and the random timing of blood sampling. We hypothesized that large sample sizes relative to traditional pharmacokinetic studies would compensate for this variability and enable the identification of pharmacogenetic predictors of drug concentrations. We performed a cross-sectional, proof-of-concept association study to replicate the well-established association between metoprolol concentrations and CYP2D6 genotype-inferred metabolizer phenotypes in participants from the Montreal Heart Institute Hospital Cohort undergoing metoprolol therapy. Plasma concentrations of metoprolol and α-hydroxymetoprolol (α-OH-metoprolol) were measured in samples collected randomly regarding the previous metoprolol dose. A total of 999 individuals were included. The metoprolol daily dose ranged from 6.25 to 400 mg (mean 84.3 ± 57.1 mg). CYP2D6-inferred phenotype was significantly associated with both metoprolol and α-OH-metoprolol in unadjusted and adjusted models (all p < 10-14 ). Models for metoprolol daily dose showed consistent results. Our study suggests that randomly drawn blood samples from biobanks can serve as a new approach to discover genetic associations related to drug concentrations and dosing, with potentially broader implications for genomewide association studies on the pharmacogenomics of drug metabolism.

Effects of Astragaloside IV on the Pharmacokinetics of Metoprolol in Rats and its Mechanism.

BACKGROND: Astragaloside IV (AST) and metoprolol are often used together to treat cardiovascular diseases, while the herb-drug interaction (HDI) between them is still unclear. OBJECTIVE: This study investigates the effect of AST on the pharmacokinetics of metoprolol in rats and its mechanism to predict the HDI. METHOD: First, IC50 value of AST on nine CYP450 enzymes in human liver microsomes (HLMs) was determined by the cocktail method. We explored the effect of AST on the pharmacokinetics of metoprolol (metabolized by CYP2D6) in vivo. Twelve male SD rats were equally divided into two groups, with or without pretreatment of AST (3 mg/kg/day) for 7 days, and they received metoprolol (27 mg/kg) by oral administration. Blood samples were determined using HPLC. Finally, the mechanism of AST was explored. RESULTS: AST exhibited a moderate inhibitory effect on CYP2D6 with IC50 value of 32.28 µM. The pharmacokinetic parameters of metoprolol were significantly altered by AST with the increase of AUC0-∞ (538.81 ± 51.41 to 1088.34 ± 86.46 µg*min/mL, P<0.05) and Cmax (6.21 ± 0.56 to 8.34 ± 0.87 µg/ml, P<0.05). The investigation of the mechanism showed AST to be an irreversible inhibitor of CYP2D6 with KI value of 2.9 µM and Kinact of 0.018 min-1, respectively. CONCLUSION: AST was found to increase the plasma exposure of metoprolol in rats. AST reduced the metabolism of metoprolol by inhibiting CYP2D6 activity. The HDI might enhance when metoprolol and AST will be applied in combination.

Pharmacokinetics and pharmacodynamics of oral and intravenous metoprolol tartrate in clinically healthy horses.

Cardiac drugs with defined pharmacological parameters in horses are limited. The objective of this study was to characterize the pharmacokinetic properties and cardiovascular effects of intravenous and oral metoprolol tartrate (MET) in horses. In a 2-period randomized cross-over design, MET was administered IV (0.04 mg/kg) and PO (6 mg/kg) once to six healthy adult horses. Horses were monitored via continuous telemetry and non-invasive blood pressure (NIBP). Blood samples were serially collected for 72 h post-administration, and concentrations were determined by LC-MS/MS. Pharmacokinetics were modeled using a 3-compartment model and non-linear least squares regression. Median (range) MET concentration was 110 (40.1-197) ng/ml collected 1 min (0.0167 h) after a bolus IV administration. Maximum concentration (Cmax ) after PO administration was 2135 (1590-4170) ng/ml at 0.5 (0.25-0.5) hours. Oral bioavailability was 54% (17-100%). Median apparent volume of distribution was 0.39 (0.17-0.58) l/kg, clearance was 12.63 (11.41-18.94) ml/kg/min, and elimination half-life was 21.1 (7.46-34.36) minutes. No clinically relevant effects of IV or PO metoprolol were noted on cardiac rhythm or NIBP. Sweating was the most common side effect. The metoprolol doses used in this study achieve plasma concentrations reported to achieve ß-blockade in humans.

Solid-phase microextraction for assessment of plasma protein binding, a complement to rapid equilibrium dialysis.

Aim: Determination of plasma protein binding (PPB) is considered vital for better understanding of pharmacokinetic and pharmacodynamic activities of drugs due to the role of free concentration in pharmacological response. Methodology & results: Solid-phase microextraction (SPME) was investigated for measurement of PPB from biological matrices and compared with a gold standard approach (rapid equilibrium dialysis [RED]). Discussion & conclusion: SPME-derived values of PPB correlated well with literature values, and those determined by RED. Respectively, average protein binding across three concentrations by RED and SPME was 33.1 and 31.7% for metoprolol, 89.0 and 86.6% for propranolol and 99.2 and 99.0% for diclofenac. This study generates some evidence for SPME as an alternative platform for the determination of PPB.

Effect of deglucuronidation on the results of the Basel phenotyping cocktail.

We investigated the effect of deglucuronidation on the plasma concentration of the constituents of the Basel phenotyping cocktail and on the interpretation of the phenotyping results under basal conditions and after cytochrome P450 (CYP) induction with metamizole. The cocktail containing caffeine (CYP1A2), efavirenz (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), metoprolol (CYP2D6) and midazolam (CYP3A4) was administered to 12 healthy subjects before (basal) and after treatment with metamizole for 1 week. In the basal state, deglucuronidation caused an increase in the plasma concentrations and area under the curve (AUC) of metoprolol, 8'-hydroxyefavirenz, 4'-hydroxyflurbiprofen and 1'-hydroxymidazolam. This effect could be visualized in Bland-Altman plots, where the values for 8'-hydroxyefavirenz, 4'-hydroxyflurbiprofen and 1'-hydroxymidazolam were mostly above the +20% threshold. As a result, the metabolic ratio (MR), calculated as AUCparent drug /AUCmetabolite , decreased with deglucuronidation for CYP2B6, CYP2C9 and CYP3A4 and increased for CYP2D6. Treatment with metamizole, a constitutive androstane receptor-dependent inducer of CYP2B6, CYP2C9, CYP2C19 and CYP3A4, accentuated the effect of deglucuronidation on AUC and MR. The correlation of MRs calculated as the plasma concentration ratio parent drug/metabolite with the MR calculated as the AUC ratio showed that 1 sample obtained between 2 and 6 hours after cocktail ingestion and analysed with and without deglucuronidation is sufficient to obtain reliable phenotyping results. Importantly, CYP2C9 and 3A4 induction would have been missed without deglucuronidation of the plasma samples. In conclusion, deglucuronidation of the plasma samples improves the stability of the phenotyping results of the Basel phenotyping cocktail and is necessary to reliably detect CYP induction.

Quantification of serum levels in mice of seven drugs (and six metabolites) commonly taken by older people with polypharmacy.

Polypharmacy (use of ≥ 5 drugs) is common in older people but has minimal preclinical or clinical evidence of safety or efficacy and is associated with adverse outcomes in older people. Drug-drug interactions are poorly understood beyond drug pairs. An efficient and sensitive method to measure multiple serum drugs and metabolites could inform drug dosing in polypharmacy. Development of a sensitive liquid chromatography - tandem mass spectrometry method to simultaneously measure seven drugs and their respective metabolites in serum in a preclinical model of polypharmacy. This method was validated for optimal recovery, matrix effect, limit of quantification (LOQ), inter- and intra-day variability, and carry over. Serum samples from mice (n = 5-6/group) treated with chronic oral doses of three polypharmacy regimens and five monotherapies were screened for drug and metabolite levels (metoprolol, α-hydroxymetoprolol, O-desmethylmetoprolol, omeprazole, 5-hydroxyomeprazole, omeprazole sulphone, acetaminophen, irbesartan, citalopram, oxybutynin, oxycodone, noroxycodone, oxymorphone and tenivastatin). The LOQ for the compounds ranged from 0.05 to 0.1 ng/mL in serum. Recovery, matrix effect, and inter- and intra-day variability peak response were acceptable. No carry over was observed at the concentrations tested. Analytes were detectable in mice treated with these drugs, and differences in drug levels were observed with different polypharmacy and monotherapy regimens. The method is sensitive and robust to measure parent drugs and metabolites simultaneously in the context of polypharmacy. Polypharmacy appeared to affect drug levels in a preclinical model. This model can be used to understand pharmacokinetics of chronic polypharmacy, which could inform prescribing and improve outcomes for older people.

Pharmacogenomics for Primary Care: An Overview.

Most of the prescribing and dispensing of medicines happens in primary care. Pharmacogenomics (PGx) is the study and clinical application of the role of genetic variation on drug response. Mounting evidence suggests PGx can improve the safety and/or efficacy of several medications commonly prescribed in primary care. However, implementation of PGx has generally been limited to a relatively few academic hospital centres, with little adoption in primary care. Despite this, many primary healthcare providers are optimistic about the role of PGx in their future practice. The increasing prevalence of direct-to-consumer genetic testing and primary care PGx studies herald the plausible gradual introduction of PGx into primary care and highlight the changes needed for optimal translation. In this article, the potential utility of PGx in primary care will be explored and on-going barriers to implementation discussed. The evidence base of several drug-gene pairs relevant to primary care will be outlined with a focus on antidepressants, codeine and tramadol, statins, clopidogrel, warfarin, metoprolol and allopurinol. This review is intended to provide both a general introduction to PGx with a more in-depth overview of elements relevant to primary care.

Examination of Metoprolol Pharmacokinetics and Pharmacodynamics Across CYP2D6 Genotype-Derived Activity Scores.

Recent CYP2D6 phenotype standardization efforts by CYP2D6 activity score (AS) are based on limited pharmacokinetic (PK) and pharmacodynamic (PD) data. Using data from two independent clinical trials of metoprolol, we compared metoprolol PK and PD across CYP2D6 AS with the goal of determining whether the PK and PD data support the new phenotype classification. S-metoprolol apparent oral clearance (CLo), adjusted for clinical factors, was correlated with CYP2D6 AS (P < 0.001). The natural log of CLo was lower with an AS of 1 (7.6 ± 0.4 mL/minute) vs. 2-2.25 (8.3 ± 0.6 mL/minute; P = 0.012), similar between an AS of 1 and 1.25-1.5 (7.8 ± 0.5 mL/minute; P = 0.702), and lower with an AS of 1.25-1.5 vs. 2-2.25 (P = 0.03). There was also a greater reduction in heart rate with metoprolol among study participants with AS of 1 (-10.8 ± 5.5) vs. 2-2.25 (-7.1 ± 5.6; P < 0.001) and no significant difference between those with an AS of 1 and 1.25-1.5 (-9.2 ± 4.7; P = 0.095). These data highlight linear trends among CYP2D6 AS and metoprolol PK and PD, but inconsistencies with the phenotypes assigned by AS based on the current standards. Overall, this case study with metoprolol suggests that utilizing CYP2D6 AS, instead of collapsing AS into phenotype categories, may be the most precise approach for utilizing CYP2D6 pharmacogenomics in clinical practice.

Simultaneous time-course measurements of metoprolol and α-hydroxyl metoprolol in fingermarks after oral administration by liquid chromatography tandem mass spectrometry.

The aim of this study was to evaluate whether fingerprints are suitable to be applied as the biometric identification samples by testing the orally administered drugs needs to be taken daily. The dosage of BETALOC® was administered to subjects following single and multiple doses and its active ingredient metoprolol and its main metabolite α-hydroxyl metoprolol were selected as the analytes. The subjects washed their hands and pressed fingertips onto glass slides at fixed sampling points (from 1 h to 7 days), and the analytes were extracted using cotton swabs 30 times followed by ultrasonic assistance in 30℃ methanol solution for 5 min with working power of 2000 W after optimization. The drugs in blood were taken from their elbow vein and deproteinized before analysis. Analysis were performed using liquid chromatography-tandem mass spectrometry (LC/MS/MS), and their concentration time course in fingerprints and blood were evaluated and compared. Results showed that metoprolol was detected 1 h after ingestion both in fingerprints and blood, while α-hydroxyl metoprolol was detected from sampling points of 2 h in fingerprint and 3 h in blood, respectively. Drugs could be detected for longer periods in blood than in fingerprint in single dose administration. However, in multiple doses, they could reach a steady detectable state in fingerprints from the fifth day after oral administration, and could serve as a more rapid and simpler alternative for drug analysis. We demonstrate that fingerprints could be applied as the biometric identification samples for orally administered drugs in multiple-doses, and could be applied to drug testing in criminal investigations.

Effect of eliglustat on the pharmacokinetics of digoxin, metoprolol, and oral contraceptives and absorption of eliglustat when coadministered with acid-reducing agents.

Eliglustat is an oral substrate reduction therapy indicated for patients with Gaucher disease type 1. Based on in vitro data, clinical trials were conducted to assess the potential for drug-drug interactions between eliglustat and digoxin (P-glycoprotein substrate), metoprolol (sensitive CYP2D6 substrate), a combined oral contraceptive (CYP3A substrate), and acid-reducing agents. Healthy subjects were enrolled in four Phase 1 clinical studies to evaluate the effect of eliglustat on the pharmacokinetics, safety, and tolerability of digoxin (N = 28), metoprolol (N = 14), and a combined oral contraceptive (N = 30) and the effect of acid-reducing agents on eliglustat pharmacokinetics, safety, and tolerability (N = 24). Coadministration resulted in increased exposure to digoxin (1.49-fold) and metoprolol (2-fold) with eliglustat, negligible effects on oral contraceptive pharmacokinetics with eliglustat, and a negligible effect of acid-reducing agents on eliglustat pharmacokinetics. Across all studies, eliglustat was well-tolerated. One serious adverse event (spontaneous abortion) and one discontinuation due to an adverse event (urinary tract infection) were reported, both during the acid-reducing agents study. When eliglustat is coadministered with medications that are P-glycoprotein or CYP2D6 substrates, lower doses of these concomitant medications may be required. Eliglustat may be coadministered with oral contraceptives and acid-reducing agents without dose modifications for either drug.

Pulmonary Delivery of Antiarrhythmic Drugs for Rapid Conversion of New-Onset Atrial Fibrillation.

Pharmacologic management of atrial fibrillation (AF) is a pressing problem. This arrhythmia afflicts >5 million individuals in the United States and prevalence is estimated to rise to 12 million by 2050. Although the pill-in-the-pocket regimen for self-administered AF cardioversion introduced over a decade ago has proven useful, significant drawbacks exist. Among these are the relatively long latency of effects in the range of hours along with potential for hypotension and other adverse effects. This experience prompted development of a new strategy for increasing plasma concentrations of antiarrhythmic drugs rapidly and for a limited time, namely, pulmonary delivery. In preclinical studies in Yorkshire pigs, intratracheal administration of flecainide was shown to cause a rapid, reproducible increase in plasma drug levels. Moreover, pulmonary delivery of flecainide converted AF to normal sinus rhythm by prolonging atrial depolarization, which slows intra-atrial conduction and seems to be directly correlated with efficacy in converting AF. The rapid rise in plasma flecainide levels optimizes its anti-AF effects while minimizing adverse influences on ventricular depolarization and contractility. A more concentrated and soluble formulation of flecainide using a novel cyclodextrin complex excipient reduced net drug delivery for AF conversion when compared to the acetate formulation. Inhalation of the beta-adrenergic blocking agent metoprolol slows ventricular rate and can also terminate AF. In human subjects, oral inhalation of flecainide acetate with a hand-held, breath-actuated nebulizer results in signature prolongation of the QRS complex without serious adverse events. Thus, pulmonary delivery is a promising advance in pharmacologic approach to management of AF.

Genetic studies of urinary metabolites illuminate mechanisms of detoxification and excretion in humans.

The kidneys integrate information from continuous systemic processes related to the absorption, distribution, metabolism and excretion (ADME) of metabolites. To identify underlying molecular mechanisms, we performed genome-wide association studies of the urinary concentrations of 1,172 metabolites among 1,627 patients with reduced kidney function. The 240 unique metabolite-locus associations (metabolite quantitative trait loci, mQTLs) that were identified and replicated highlight novel candidate substrates for transport proteins. The identified genes are enriched in ADME-relevant tissues and cell types, and they reveal novel candidates for biotransformation and detoxification reactions. Fine mapping of mQTLs and integration with single-cell gene expression permitted the prioritization of causal genes, functional variants and target cell types. The combination of mQTLs with genetic and health information from 450,000 UK Biobank participants illuminated metabolic mediators, and hence, novel urinary biomarkers of disease risk. This comprehensive resource of genetic targets and their substrates is informative for ADME processes in humans and is relevant to basic science, clinical medicine and pharmaceutical research.

Interrogation of CYP2D6 Structural Variant Alleles Improves the Correlation Between CYP2D6 Genotype and CYP2D6-Mediated Metabolic Activity.

The cytochrome P450 2D6 (CYP2D6) gene locus is challenging to accurately genotype due to numerous single nucleotide variants and complex structural variation. Our goal was to determine whether the CYP2D6 genotype-phenotype correlation is improved when diplotype assignments incorporate structural variation, identified by the bioinformatics tool Stargazer, with next-generation sequencing data. Using CYP2D6 activity measured with substrates dextromethorphan and metoprolol, activity score explained 40% and 34% of variability in metabolite formation rates, respectively, when diplotype calls incorporated structural variation, increasing from 36% and 31%, respectively, when diplotypes did not incorporate structural variation. We also investigated whether the revised Clinical Pharmacogenetics Implementation Consortium (CPIC) recommendations for translating genotype to phenotype improve CYP2D6 activity predictions over the current system. Although the revised recommendations do not improve the correlation between activity score and CYP2D6 activity, perhaps because of low frequency of the CYP2D6*10 allele, the correlation with metabolizer phenotype group was significantly improved for both substrates. We also measured the function of seven rare coding variants: one (A449D) exhibited decreased (44%) and another (R474Q) increased (127%) activity compared with reference CYP2D6.1 protein. Allele-specific analysis found that A449D is part of a novel CYP2D6*4 suballele, CYP2D6*4.028. The novel haplotype containing R474Q was designated CYP2D6*138 by PharmVar; another novel haplotype containing R365H was designated CYP2D6*139. Accuracy of CYP2D6 phenotype prediction is improved when the CYP2D6 gene locus is interrogated using next-generation sequencing coupled with structural variation analysis. Additionally, revised CPIC genotype to phenotype translation recommendations provides an improvement in assigning CYP2D6 activity.