Therapeutic drug monitoring, liquid biopsies or pharmacogenomics for prediction of human drug metabolism and response.

Pharmacokinetics plays a central role in understanding the significant interindividual differences that exist in drug metabolism and response. Effectively addressing these differences requires a multi-faceted approach that encompasses a variety of tools and methods. In this review, we examine three key strategies to achieve this goal, namely pharmacogenomics, therapeutic drug monitoring (TDM) and liquid biopsy-based monitoring of hepatic ADME gene expression and highlight their advantages and limitations. We note that larger cohort studies are needed to validate the utility of liquid biopsy-based assessment of hepatic ADME gene expression, which includes prediction of drug metabolism in the clinical setting. Modern mass spectrometers have improved traditional TDM methods, offering versatility and sensitivity. In addition, the identification of endogenous or dietary markers for CYP metabolic traits offers simpler and more cost-effective alternatives to determine the phenotype. We believe that future pharmacogenomic applications in clinical practice should prioritize the identification of missing heritable factors, using larger, well-characterized patient studies and controlling for confounding factors such as diet, concomitant medication and physical health. The intricate regulation of ADME gene expression implies that large-scale studies combining long-read next-generation sequencing (NGS) of complete genomes with phenotyping of patients taking different medications are essential to identify these missing heritabilities. The continuous integration of such data into AI-driven analytical systems could provide a comprehensive and useful framework. This could lead to the development of highly effective algorithms to improve genetics-based precision treatment by predicting drug metabolism and response, significantly improving clinical outcomes.

Combined effect of CYP2C19 and CYP2D6 genotypes on escitalopram serum concentration and its metabolic ratio in a European patient population.

AIMS: The aim of the present study was to investigate the impact of CYP2D6 genotype on exposure and metabolism of escitalopram in patients stratified by CYP2C19 genotype in a large real-world population. METHODS: Patients were included from a therapeutic drug monitoring service if they had measured serum concentration of escitalopram and the metabolite, N-desmethyl escitalopram, and performed CYP2C19 and CYP2D6 genotyping. Patients were divided into 16 combined genotype-predicted phenotype subgroups (poor [PM], intermediate [IM], normal [NM] and ultrarapid metabolizers [UM]) of CYP2C19/CYP2D6. The concentration-to-dose (CD) ratio and metabolite-to-parent ratio (metabolic ratio) of escitalopram were compared across subgroups using the Kruskal-Wallis test followed by Dunn's test with CYP2D6 NMs as the reference group. RESULTS: A total of 5067 patients were included in the study. A stepwise increase in escitalopram CD ratio by decreasing CYP2D6 activity was observed in all CYP2C19 subgroups, except for in CYP2C19 UMs. The percentage differences in escitalopram CD ratio between CYP2D6 PMs and NMs were 24% in CYP2C19 NMs (P < .001), 28% in CYP2C19 IMs (P < .001) and 31% in CYP2C19 PMs (P = .04). As for the CD ratio, CYP2D6 genotype effect on metabolic ratio increased stepwise by decreasing CYP2C19 metabolism. CONCLUSIONS: CYP2D6 genotype is of significant importance for the individual variation in escitalopram pharmacokinetics. The most relevant increase in escitalopram concentration is seen in individuals with decreased and/or absent CYP2C19 activity. By combining CYP2C19 and CYP2D6 genotypes, the optimal dose for patients may be predicted with greater precision than for CYP2C19 genotype alone.

Evidence for solanidine as a dietary CYP2D6 biomarker: Significant correlation with risperidone metabolism.

AIMS: The extensive variability in cytochrome P450 2D6 (CYP2D6) metabolism is mainly caused by genetic polymorphisms. However, there is large, unexplained variability in CYP2D6 metabolism within CYP2D6 genotype subgroups. Solanidine, a dietary compound found in potatoes, is a promising phenotype biomarker predicting individual CYP2D6 metabolism. The aim of this study was to investigate the correlation between solanidine metabolism and the CYP2D6-mediated metabolism of risperidone in patients with known CYP2D6 genotypes. METHODS: The study included therapeutic drug monitoring (TDM) data from CYP2D6-genotyped patients treated with risperidone. Risperidone and 9-hydroxyrisperidone levels were determined during TDM, and reprocessing of the respective TDM full-scan high-resolution mass spectrometry files was applied for semi-quantitative measurements of solanidine and five metabolites (M402, M414, M416, M440 and M444). Spearman's tests determined the correlations between solanidine metabolic ratios (MRs) and the 9-hydroxyrisperidone-to-risperidone ratio. RESULTS: A total of 229 patients were included. Highly significant, positive correlationswere observed between all solanidine MRs and the 9-hydroxyrisperidone-to-risperidone ratio (ρ > 0.6, P < .0001). The strongest correlation was observed for the M444-to-solanidine MR in patients with functional CYP2D6 metabolism, i.e., genotype activity scores of 1 and 1.5 (ρ 0.72-0.77, P < .0001). CONCLUSION: The present study shows strong, positive correlations between solanidine metabolism and CYP2D6-mediated risperidone metabolism. The strong correlation within patients carrying CYP2D6 genotypes encoding functional CYP2D6 metabolism suggests that solanidine metabolism may predict individual CYP2D6 metabolism, and hence potentially improve personalized dosing of drugs metabolized by CYP2D6.

Novel Identification of Cysteinyl Derivatives of Toxic Clozapine Nitrenium Ions and the Effect of Valproic Acid on Metabolite Formation: A Study Using Reprocessed High-Resolution Mass Spectra of Analyzed Therapeutic Drug Monitoring Samples.

BACKGROUND: Clozapine (CLZ) use is hampered by the risk of granulocyte toxicity, which is associated with the formation of nitrenium ions and the concurrent use of valproic acid (VPA). These highly reactive nitrenium ions cannot be measured in vivo. Instead, deactivated cysteinyl conjugates may potentially be detected. The aim of this study was to develop a novel method for identifying cysteinylated derivates of CLZ nitrenium ions to investigate the effect of VPA on their formation using therapeutic drug monitoring data. METHODS: A population comprising 93 VPA comedicated and 162 control patients from a therapeutic drug monitoring (TDM) service in Oslo, Norway, was included. Reprocessing of ultraperformance liquid chromatography high-resolution mass spectra (UHPLC-HR-MS) of previously analyzed TDM samples, combined with the assessment of MS/MS fragmentation patterns, was performed to identify the CLZ cysteinyl conjugates. Smoking, which induces CLZ metabolism, was assessed by detecting cotinine in the reprocessed mass spectra. RESULTS: By reprocessing the UHPLC-HR-MS files of the TDM analyses and reviewing the MS/MS fragment profiles, four cysteinyl conjugates of CLZ were identified. The formations of CLZ cysteinyl (CLZ-Cys 1+ ) and CLZ- N -oxide cysteinyl (CLZ-NOX-Cys 1+ ) were 1.5-fold ( P = 0.038) and 2.1-fold ( P < 0.001) higher in VPA-treated patients than those in the controls. In agreement with previous studies, a 45% reduction in N -desmethylclozapine formation was observed in VPA-treated patients ( P < 0.001). CONCLUSIONS: A novel method for detecting cysteinyl conjugates of CLZ was developed. Application of this method indicated that VPA significantly increased the formation of CLZ-Cys 1+ metabolites, which might explain the granulocyte toxicity reported after adding VPA to CLZ treatment. The developed method opens new avenues for investigating CLZ toxicity, e.g. by correlating cysteinyl conjugates and granulocyte counts in patients.

Age of onset for increased dose-adjusted serum concentrations of antidepressants and association with sex and genotype: An observational study of 34,777 individuals.

PURPOSE: The aim of this study was to examine the age of onset for increased dose-adjusted serum concentrations (C/D ratio) of common antidepressant drugs and to explore the potential association with sex and CYP2C19/CYP2D6 genotype. METHODS: Serum concentrations and prescribed daily doses for citalopram, escitalopram, sertraline, venlafaxine and mirtazapine, and CYP genotypes, were obtained from a therapeutic drug monitoring (TDM) service. Segmented linear regression analysis was used to examine the relationship between age and antidepressant log C/D ratio in (i) all individuals, (ii) men and women, and (iii) CYP2D6/CYP2C19 normal metabolizers (NMs) and CYP2D6/CYP2C19 intermediate or poor metabolizers (IMs/PMs). RESULTS: A total of 34,777 individuals were included in the study; CYP genotype was available for 21.3%. An increase in C/D ratio started at 44‒55 years of age. Thereafter, the increase progressed more rapidly for citalopram and escitalopram than for venlafaxine and mirtazapine. A doubled C/D ratio was estimated to occur at 79 (citalopram), 81 (escitalopram), 86 (venlafaxine), and 90 years (mirtazapine). For sertraline, only modest changes in C/D ratio were observed. For escitalopram and venlafaxine, the observed increase in C/D ratio started earlier in women than in men. The results regarding CYP genotype were inconclusive. CONCLUSION: The age-related increase in C/D ratio starts in middle-aged adults and progresses up to more than twofold higher C/D ratio in the oldest old. Sertraline seems to be less prone to age-related changes in C/D ratio than the other antidepressants.

Impact of CYP2D6*2, CYP2D6*35, rs5758550, and related haplotypes on risperidone clearance in vivo.

PURPOSE: The CYP2D6 gene exhibits significant polymorphism, contributing to variability in responses to drugs metabolized by CYP2D6. While CYP2D6*2 and CYP2D6*35 are presently designated as alleles encoding normal metabolism, this classification is based on moderate level evidence. Additionally, the role of the formerly called "enhancer" single nucleotide polymorphism (SNP) rs5758550 is unclear. In this study, the impacts of CYP2D6*2, CYP2D6*35 and rs5758550 on CYP2D6 activity were investigated using risperidone clearance as CYP2D6 activity marker. METHODS: A joint parent-metabolite population pharmacokinetic model was used to describe 1,565 serum concentration measurements of risperidone and 9-hydroxyrisperidone in 512 subjects. Risperidone population clearance was modeled as the sum of a CYP2D6-independent clearance term and the partial clearances contributed from each individually expressed CYP2D6 allele or haplotype. In addition to the well-characterized CYP2D6 alleles (*3-*6, *9, *10 and *41), *2, *35 and two haplotypes assigned as CYP2D6*2-rs5758550G and CYP2D6*2-rs5758550A were evaluated. RESULTS: Each evaluated CYP2D6 allele was associated with significantly lower risperidone clearance than the reference normal function allele CYP2D6*1 (p < 0.001). Further, rs5758550 differentiated the effect of CYP2D6*2 (p = 0.005). The haplotype-specific clearances for CYP2D6*2-rs5758550A, CYP2D6*2-rs5758550G and CYP2D6*35 were estimated to 30%, 66% and 57%, respectively, relative to the clearance for CYP2D6*1. Notably, rs5758550 is in high linkage disequilibrium (R2 > 0.85) with at least 24 other SNPs and cannot be assigned as a functional SNP. CONCLUSION: CYP2D6*2 and CYP2D6*35 encode reduced risperidone clearance, and the extent of reduction for CYP2D6*2 is differentiated by rs5758550. Genotyping of these haplotypes might improve the precision of genotype-guided prediction of CYP2D6-mediated clearance.

Dose-dependent effect of lamotrigine on quetiapine serum concentration in patients using instant release tablets.

PURPOSE: Lamotrigine was previously reported to reduce serum concentration of quetiapine. The aim of this study was to investigate whether lamotrigine dose or quetiapine formulation was of importance for the drug interaction. METHODS: Patients combining lamotrigine with quetiapine (cases) were included retrospectively from a routine therapeutic drug monitoring (TDM) service, as were a control group of patients using quetiapine without any interacting drugs. The case and control groups were divided into groups using immediate release (IR) and extended release (XR) quetiapine. The case group was further split into high-dose (> 200 mg/day) and low-dose (≤ 200 mg/day) lamotrigine users. Quetiapine concentration-to-dose (C/D) ratio and metabolite-to-parent ratio (MPR) were compared between the control group and dose-separated case groups using ANOVA test and t-tests. RESULTS: In total, 406 patients were included. The mean C/D ratio of IR quetiapine was 46% lower in the high-dose lamotrigine group compared with the control group (P < 0.001), while no interaction effect was present in the low dose lamotrigine group (P = 0.7). Regardless of lamotrigine dose, there was no difference in quetiapine C/D ratio for patients using the XR formulation (P = 0.4). The quetiapine MPR was unaffected regardless of formulation and lamotrigine dose (P ≥ 0.06). CONCLUSION: The effect of lamotrigine in reducing quetiapine concentration is only significant for patients using quetiapine IR tablets who are treated with lamotrigine doses > 200 mg/day. Because of high variability in the interaction effect, TDM of quetiapine should be recommended during co-prescription of high-dose lamotrigine.

Effect of CYP2D6 and CYP2C19 genotypes on atomoxetine serum levels: A study based on therapeutic drug monitoring data.

AIMS: Atomoxetine is mainly metabolized by CYP2D6 while CYP2C19 plays a secondary role. It is known that patients carrying genotypes encoding decreased/absent CYP2D6 metabolism obtain higher atomoxetine concentrations and are at increased risk of adverse effects. Here, we aimed to investigate the added effects of reduced-function CYP2C19 genotype on atomoxetine concentrations in real-world settings. METHODS: Serum atomoxetine concentrations and CYP2D6/2C19 genotypes were included from a therapeutic drug monitoring service. Patients were first subgrouped according to CYP2D6 encoding normal, reduced or absent CYP2D6 metabolism, referred to as normal (NM), intermediate (IM) or poor metabolizers (PM). Then, the effect of reduced-function CYP2C19 genotypes was investigated. Genotyping of the CYP2D6 nonfunctional or reduced variant alleles comprised CYP2D6*3-*6, *9-*10 and *41. For CYP2C19, the CYP2C19*2 was analysed to define metabolizer phenotype. Dose-adjusted serum atomoxetine concentration was the exposure measure. RESULTS: Using a patient cohort (n = 315), it was found that CYP2D6 IM and PM patients had 1.9-fold (95% confidence interval: 1.4-2.7) and 9.6-fold (5.9-16) higher exposure of atomoxetine compared with CYP2D6 NMs. CYP2C19*2 carriers had 1.5-fold (1.1-2.2) higher atomoxetine exposure than noncarriers regardless of CYP2D6 genotype. CONCLUSION: CYP2D6 genotype has a great impact on atomoxetine exposure, where our real-world data suggest atomoxetine dose requirements to be around half and 1/10 in CYP2D6 IM and PM vs. NM patients, respectively. When adding CYP2C19 genotype as a factor of relevance for personalized atomoxetine dosing, CYP2C19*2 carriers should further reduce the dose by a third. These findings suggest that pre-emptive CYP2D6/CYP2C19 genotyping should be performed to individualize atomoxetine dosing and prevent adverse effects.

Impact of age, sex and cytochrome P450 genotype on quetiapine and N-desalkylquetiapine serum concentrations: A study based on real-world data from 8118 patients.

AIMS: To investigate the effect of aging, sex and cytochrome P450 (CYP) genotypes on the exposure of quetiapine (QUE) and the pharmacologically active metabolite N-desalkylquetiapine (NDQ). METHODS: Patients with serum concentrations of QUE and NDQ were included retrospectively from a therapeutic drug monitoring service. The outcome measures were concentration:dose (C:D) ratios of QUE and NDQ, and NDQ:QUE metabolic ratio. Linear mixed model analyses were used to evaluate the effects of age, sex and, subsequently, CYP2D6/3A genotypes. RESULTS: The average age of the included population (n = 8118 patients) was 44 years (13.5% ≥65 years). The C:D ratio of QUE and NDQ gradually increased in patients aged >50 years compared to those aged 18-30 years, with 28 and 29% increase, respectively, for patients aged >70 years (P < .001). Compared to males, females had 15% lower QUE C:D ratio and 10% higher C:D ratio of NDQ (both P < .001). The NDQ:QUE metabolic ratio was 30% higher in females than in males (P < .001). For females ≥65 years, the NDQ C:D ratio was 36% higher compared to males <65 years (P < .001). A significantly higher NDQ C:D ratio was observed for CYP2D6 intermediate (+7%, P = .012) and poor (+17%, P = .001) compared to normal metabolizers. No effects of CYP3A4*22 and CYP3A5*1 allele variants were observed. CONCLUSION: This study shows an increase of the QUE and NDQ exposures during aging. Old age, female sex and CYP2D6 allele variants encoding reduced activity are factors associated with high NDQ exposure. Therefore, females ≥65 years carrying CYP2D6 allele variants encoding reduced activity have the highest risk of dose-dependent side effects of NDQ during QUE treatment.

Implementation of pharmacogenetic testing in medication reviews in a hospital setting.

AIM: To investigate whether it is feasible to perform pharmacogenetic testing and implement the test results as part of medication reviews during hospitalization of multimorbid patients. METHODS: Patients with ≥2 chronic conditions and ≥5 regular drugs with at least one potential gene-drug interaction (GDI) were included from one geriatric and one cardiology ward for pharmacogenetic testing. After inclusion by the study pharmacist, blood samples were collected and shipped to the laboratory for analysis. For patients still hospitalized at the time when the pharmacogenetic test results were available, the information was used in medication reviews. Recommendations from the pharmacist on actionable GDIs were communicated to the hospital physicians, who subsequently decided on potential immediate changes or forwarded suggestions in referrals to general practitioners. RESULTS: The pharmacogenetic test results were available for medication review in 18 of the 46 patients (39.1%), where median length of hospital stay was 4.7 days (1.6-18.3). The pharmacist recommended medication changes for 21 of 49 detected GDIs (42.9%). The hospital physicians accepted 19 (90.5%) of the recommendations. The most commonly detected GDIs involved metoprolol (CYP2D6 genotype), clopidogrel (CYP2C19 genotype) and atorvastatin (CYP3A4/5 and SLCOB1B1 genotype). CONCLUSIONS: The study shows that implementation of pharmacogenetic testing for medication review of hospitalized patients has the potential to improve drug treatment before being transferred to primary care. However, the logistics workflow needs to be further optimized, as test results were available during hospitalization for less than half of the patients included in the study.

Impact of CYP2D6 Genotype on Paroxetine Serum Concentration.

BACKGROUND: Paroxetine is a selective serotonin reuptake inhibitor metabolized by cytochrome P450 (CYP)2D6. Only small-scale studies have reported the impact of CYP2D6 genotype on paroxetine exposure, and international guidelines differ in their recommendations on whether paroxetine should be administered according to CYP2D6 genotype. To clarify this issue, the aim of the present study was to investigate the impact of CYP2D6 genotype on paroxetine serum concentration in a large population of patients after adjusting for CYP2C19 genotype, age, and sex. METHODS: Patients from a therapeutic drug monitoring database with records on their paroxetine serum concentrations and CYP2D6 and CYP2C19 genotyping between 2010 and 2021 were included in the study. The impact of CYP2D6 and CYP2C19 genotypes, age, and sex on the paroxetine concentration-to-dose (C/D) ratio was investigated by multiple linear regression analysis. Patients treated with relevant CYP inhibitors or inducers were excluded. RESULTS: In total, 304 patients were included in the study: 17 CYP2D6 poor metabolizers (PMs), 114 intermediate metabolizers (IMs), 168 extensive metabolizers (EMs), and 5 ultrarapid metabolizers. Multiple linear regression analysis showed that CYP2D6 IMs and PMs had 2.2-fold and 3.8-fold higher paroxetine C/D-ratios than extensive metabolizers, respectively ( P < 0.001). Patients who were CYP2C19 IMs (n = 70) or PMs (n = 13) had 1.6-fold higher paroxetine C/D ratio than extensive metabolizers ( P = 0.04). An age ≥65 years was associated with a 2.9-fold increased C/D ratio ( P < 0.001), whereas sex was not significantly associated with paroxetine exposure. CONCLUSIONS: The present study showed that CYP2D6 genotype is of significant importance for paroxetine dose adjustments. For CYP2D6 PMs, 25% of the regular paroxetine starting dose may be sufficient, whereas CYP2D6 IMs could receive 50% of the regular dosage. This well-powered study shows that the guidelines should consider the importance of CYP2D6 genotype for personalized dosing of paroxetine.

Prediction of CYP2D6 poor metabolizers by measurements of solanidine and metabolites-a study in 839 patients with known CYP2D6 genotype.

PURPOSE: Poor metabolizers (PMs) of the highly polymorphic enzyme CYP2D6 are usually at high risk of adverse effects during standard recommended dosing of CYP2D6-metabolized drugs. We studied if the metabolism of solanidine, a dietary compound found in potatoes, could serve as a biomarker predicting the CYP2D6 PM phenotype for precision dosing. METHODS: The study included 839 CYP2D6-genotyped patients who were randomized by a 4:1 ratio into test or validation cohorts. Full-scan high-resolution mass spectrometry data files of previously analyzed serum samples were reprocessed for identification and quantification of solanidine and seven metabolites. Metabolite-to-solanidine ratios (MRs) of the various solanidine metabolites were calculated prior to performing receiver operator characteristic (ROC) and multiple linear regression analyses on the test cohort. The MR thresholds obtained from the ROC analyses were tested for the prediction of CYP2D6 PMs in the validation cohort. RESULTS: In the test cohort, the M414-to-solanidine MR attained the highest sensitivity and specificity parameters from the ROC analyses (0.98 and 1.00) and highest explained variance from the linear models (R2 = 0.68). Below these thresholds, CYP2D6 PM predictions were tested in the validation cohort providing positive and negative predictive values of 100% for the MR of M414, while similar values for the other MRs ranged from 20.5 to 73.3% and 96.7 to 99.3%, respectively. CONCLUSION: The M414-to-solanidine MR is an excellent predictor of the CYP2D6 PM phenotype. By measuring solanidine and metabolites using liquid chromatography-mass spectrometry in patient serum samples, CYP2D6 PMs can easily be identified, hence facilitating the implementation of precision dosing in clinical practice.

Association Between CYP2D6 Metabolizer Status and Vortioxetine Exposure and Treatment Switching: A Retrospective, Naturalistic Cohort Study Using Therapeutic Drug Monitoring Data From 640 Patients.

PURPOSE: The antidepressant vortioxetine is mainly metabolized by the polymorphic enzyme CYP2D6. The aim of this study was to investigate the absolute serum concentrations of vortioxetine and frequency of switching to an alternative antidepressant in relation to CYP2D6 genotype in a naturalistic patient population. METHODS: The analyses included data from 640 CYP2D6 -genotyped patients treated with vortioxetine from a Norwegian therapeutic drug monitoring database. Serum concentration of vortioxetine was determined using ultrahigh-performance liquid chromatography-high-resolution mass spectrometry, whereas longitudinal reviews of therapeutic drug monitoring profiles were performed to identify cases of patients switching from vortioxetine to an alternative antidepressant. RESULTS: Compared with CYP2D6 normal metabolizers (n = 342), the median vortioxetine serum concentration (ng/mL) was 2.1-fold ( P < 0.001) increased in poor metabolizers (PMs) (n = 48), 1.5-fold ( P < 0.001) increased in intermediate metabolizers (n = 238), and not significantly changed in ultrarapid metabolizers (n = 12). Compared with CYP2D6 normal metabolizers, treatment switch from vortioxetine to alternative antidepressants was 5.1-fold (95% confidence interval, 1.6-15.4, P = 0.003) more frequent among PMs. The prescribed doses did not differ significantly between the subgroups ( P = 0.26). A possible explanation for the increased frequency of treatment switch among PMs is that concentration-dependent adverse events were more frequent in this group because of increased drug exposure. CONCLUSIONS: This naturalistic study provides novel data on the association between CYP2D6 genotype and treatment switch of vortioxetine, which likely reflects the significant effect of CYP2D6 genotype on vortioxetine exposure.

Effect of Valproic Acid on the Metabolic Spectrum of Clozapine in Patients With Schizophrenia.

BACKGROUND: Valproic acid (VPA) is frequently used with clozapine (CLZ) as mood stabilizer and/or seizure prophylaxis. Valproic acid is known to reduce N-desmethylclozapine (N-DMC) but not CLZ levels. This leads to the hypothesis that VPA induces the CLZ metabolism via non-N-desmethylation pathways. Therefore, we aimed to investigate the effect of concurrent VPA use on the serum concentrations of a spectrum of CLZ metabolites in patients, adjusting for smoking. METHODS: In total, 288 patients with an overall number of 737 serum concentration measurements of CLZ and metabolites concurrently using VPA (cases, n = 22) or no interacting drugs (controls, n = 266) were included from a routine therapeutic drug monitoring service. Linear mixed model analyses were performed to compare the dose-adjusted concentrations (C/D) of CLZ, N-DMC, CLZ 5N/N+-glucuronides, and metabolite-to-parent ratios in cases versus controls. RESULTS: After adjusting for covariates, the N-DMC (-40%, P < 0.001) and N+-glucuronide C/Ds (-78%, P < 0.001) were reduced in cases versus controls, while the CLZ C/D was unchanged (P > 0.7). In contrast, the 5N-glucuronide C/D (+250%, P < 0.001) and 5N-glucuronide-to-CLZ ratios (+120%, P = 0.01) were increased in cases versus controls. CONCLUSIONS: Our findings show that complex changes in CLZ metabolism underly the pharmacokinetic interaction with VPA. The lower levels of N-DMC seem to be caused by VPA-mediated induction of CLZ 5N-glucuronide formation, subsequently leading to reduced substrate availability for N-desmethylation. Whether the changes in CLZ metabolism caused by VPA affects the clinical outcome warrants further investigation.

Metabolite Profiling of Clozapine in Patients Switching Versus Maintaining Treatment: A Retrospective Pilot Study.

PURPOSE/BACKGROUND: Pharmacokinetics may be of relevance for the risk of clozapine discontinuation. We compared metabolite profiles, accounting for smoking habits, in patients switching versus maintaining clozapine treatment at therapeutic concentrations. METHODS/PROCEDURES: Adult patients with clozapine serum levels above 1070 nmol/L (350 ng/mL) were retrospectively included from a Norwegian therapeutic drug monitoring service during 2018-2020. Inclusion criteria were (1) known smoking habits, (2) blood sample drawn within 10 to 30 hours after last clozapine intake, and (3) detectable levels of N -desmethylclozapine, clozapine -N -oxide, clozapine-5 N -glucuronide, or clozapine- N + - glucuronide. Patients comedicated with cytochrome P450 enzyme inducers, inhibitors, or valproic acid were excluded. The high-resolution mass spectrometry assay enabled detection of 21 clozapine metabolites. Metabolite profiles were compared between patients switching treatment (switchers), measured as clozapine being replaced by another antipsychotic drug in blood samples, versus maintaining clozapine treatment (nonswitchers) during the study period. FINDINGS/RESULTS: Of the 84 patients fulfilling the study criteria, 7 patients (8.3%) were identified as clozapine switchers. After correcting for smoking habits, the clozapine-5 N -glucuronide/clozapine ratio was 69% lower ( P < 0.001), while the clozapine- N + -glucuronide/clozapine-5 N -glucuronide ratio was 143% higher ( P = 0.026), respectively, in switchers versus nonswitchers. The other metabolite ratios did not significantly differ between switchers and nonswitchers. IMPLICATIONS/CONCLUSIONS: The present study found a significantly reduced 5 N -glucuronidation phenotype in patients switching from clozapine at therapeutic serum concentrations (>1070 nmol/L) to other antipsychotic drugs. This may indicate that glucuronidation, as a potential detoxification mechanism, is related to clozapine tolerability. However, the causality of this observation needs to be investigated in future studies with larger patient populations.

Identification of Escitalopram Metabolic Ratios as Potential Biomarkers for Predicting CYP2C19 Poor Metabolizers.

BACKGROUND: Escitalopram is metabolized by CYP2C19 to N-desmethyl escitalopram and escitalopram propionic acid. The primary aims of this study were to investigate the impact of the CYP2C19 phenotype on metabolic ratios of escitalopram in vivo and propose a biomarker for the CYP2C19 phenotype in patients treated with escitalopram. METHODS: Median steady-state serum metabolite/parent drug ratio of N-desmethyl escitalopram and escitalopram propionic acid was investigated across CYP2C19 genotype-translated phenotype groups. The receiver operator characteristics method and the area-under-the-receiver-operator-characteristics curve was used to determine the best suited metabolic ratio for detecting CYP2C19 poor metabolizers (PMs). RESULTS: A total of 441 patients were included in the study. The N-desmethyl escitalopram/escitalopram ratio was 67% and 44% lower in CYP2C19 PMs and intermediate metabolizers (IMs), respectively, than normal metabolizers. Furthermore, the ability of the ratio to predict CYP2C19 PMs was 92%. A metabolic ratio of <0.24 was detected in 8 of 8 PMs in the study, indicating that it is a promising biomarker of reduced CYP2C19 activity. The escitalopram propionic acid/escitalopram ratio was 77% and 48% lower in CYP2C19 PMs and IMs, respectively; however, the ability of the ratio to detect CYP2C19 PMs was only 87%. CONCLUSIONS: These findings suggest that DECT/ECT reflects CYP2C19 activity, and a metabolic ratio of <0.24 strongly predicts CYP2C19 PM phenotype. The ratio could be a valuable alternative to genotyping in personalized dosing of escitalopram and possibly other CYP2C19 substrates. The escitalopram propionic acid/escitalopram ratio was also associated with CYP2C19 activity; however, the ratio was inferior to the DECT/ECT at predicting PMs.

Co-prescription of metoprolol and CYP2D6-inhibiting antidepressants before and after implementation of an optimized drug interaction database in Norway.

PURPOSE: To compare the co-prescription of metoprolol and potent CYP2D6-inhibiting antidepressants before and during a 10-year period after implementation of an optimized drug interaction database into clinical decision support systems in Norway. METHODS: The study was a retrospective, cross-sequential nationwide analysis of drug-dispensing data retrieved from the Norwegian Prescription Database over a 1-year period before (2007) and two 1-year periods after (2012 and 2017) implementation of a drug interaction database providing recommendations on non-interacting alternative medications. Primary outcome was changes in co-prescription rates of metoprolol and the potent CYP2D6-inhibiting antidepressants fluoxetine, paroxetine, or bupropion relative to alternative antidepressants with no or limited CYP2D6 inhibitory potential. To control for potential secular trend bias, a comparison group consisting of atenolol/bisoprolol users was included. RESULTS: The co-prescription rate of metoprolol with potent CYP2D6 inhibitors declined following implementation of the optimized database, by 21% (P < 0.001) after 5 years and by 40% (P < 0.001) after 10 years. Compared with atenolol/bisoprolol users, patients treated with metoprolol had significantly reduced likelihood of being prescribed a CYP2D6-inhibiting antidepressant in the two post-implementation periods (OR 0.61 (95% CI 0.54-0.69) and OR 0.45 (95% CI 0.40-0.51), respectively, versus OR 0.84 (95% CI 0.74-0.94) prior to implementation). Small and mostly insignificant differences in average daily metoprolol dosage were found between patients treated with the various antidepressants. CONCLUSION: The present study suggests that implementation of a drug interaction database providing recommendations on non-interacting drug alternatives contributes to reduced co-prescribing of drug combinations associated with potentially serious adverse effects.

Correlations between 4ß-hydroxycholesterol and hepatic and intestinal CYP3A4: protein expression, microsomal ex vivo activity, and in vivo activity in patients with a wide body weight range.

PURPOSE: Variability in cytochrome P450 3A4 (CYP3A4) metabolism is mainly caused by non-genetic factors, hence providing a need for accurate phenotype biomarkers. Although 4ß-hydroxycholesterol (4ßOHC) is a promising endogenous CYP3A4 biomarker, additional investigations are required to evaluate its ability to predict CYP3A4 activity. This study investigated the correlations between 4ßOHC concentrations and hepatic and intestinal CYP3A4 protein expression and ex vivo microsomal activity in paired liver and jejunum samples, as well as in vivo CYP3A4 phenotyping (midazolam) in patients with a wide body weight range. METHODS: The patients (n = 96; 78 with obesity and 18 normal or overweight individuals) were included from the COCKTAIL-study (NCT02386917). Plasma samples for analysis of 4ßOHC and midazolam concentrations, and liver (n = 56) and jejunal (n = 38) biopsies were obtained. The biopsies for determination of CYP3A4 protein concentration and microsomal activity were obtained during gastric bypass or cholecystectomy. In vivo CYP3A4 phenotyping was performed using semi-simultaneous oral (1.5 mg) and intravenous (1.0 mg) midazolam. RESULTS: 4ßOHC concentrations were positively correlated with hepatic microsomal CYP3A4 activity (ρ = 0.53, p < 0.001), and hepatic CYP3A4 concentrations (ρ = 0.30, p = 0.027), but not with intestinal CYP3A4 concentrations (ρ = 0.18, p = 0.28) or intestinal microsomal CYP3A4 activity (ρ = 0.15, p = 0.53). 4ßOHC concentrations correlated weakly with midazolam absolute bioavailability (ρ = - 0.23, p = 0.027) and apparent oral clearance (ρ = 0.28, p = 0.008), but not with systemic clearance (ρ = - 0.03, p = 0.81). CONCLUSION: These findings suggest that 4ßOHC concentrations reflect hepatic, but not intestinal, CYP3A4 activity. Further studies should investigate the potential value of 4ßOHC as an endogenous biomarker for individual dose requirements of intravenously administered CYP3A4 substrate drugs. TRIAL REGISTRATION: Clinical. TRIALS: gov identifier: NCT02386917.

An International Adult Guideline for Making Clozapine Titration Safer by Using Six Ancestry-Based Personalized Dosing Titrations, CRP, and Clozapine Levels.

This international guideline proposes improving clozapine package inserts worldwide by using ancestry-based dosing and titration. Adverse drug reaction (ADR) databases suggest that clozapine is the third most toxic drug in the United States (US), and it produces four times higher worldwide pneumonia mortality than that by agranulocytosis or myocarditis. For trough steady-state clozapine serum concentrations, the therapeutic reference range is narrow, from 350 to 600 ng/mL with the potential for toxicity and ADRs as concentrations increase. Clozapine is mainly metabolized by CYP1A2 (female non-smokers, the lowest dose; male smokers, the highest dose). Poor metabolizer status through phenotypic conversion is associated with co-prescription of inhibitors (including oral contraceptives and valproate), obesity, or inflammation with C-reactive protein (CRP) elevations. The Asian population (Pakistan to Japan) or the Americas' original inhabitants have lower CYP1A2 activity and require lower clozapine doses to reach concentrations of 350 ng/mL. In the US, daily doses of 300-600 mg/day are recommended. Slow personalized titration may prevent early ADRs (including syncope, myocarditis, and pneumonia). This guideline defines six personalized titration schedules for inpatients: 1) ancestry from Asia or the original people from the Americas with lower metabolism (obesity or valproate) needing minimum therapeutic dosages of 75-150 mg/day, 2) ancestry from Asia or the original people from the Americas with average metabolism needing 175-300 mg/day, 3) European/Western Asian ancestry with lower metabolism (obesity or valproate) needing 100-200 mg/day, 4) European/Western Asian ancestry with average metabolism needing 250-400 mg/day, 5) in the US with ancestries other than from Asia or the original people from the Americas with lower clozapine metabolism (obesity or valproate) needing 150-300 mg/day, and 6) in the US with ancestries other than from Asia or the original people from the Americas with average clozapine metabolism needing 300-600 mg/day. Baseline and weekly CRP monitoring for at least four weeks is required to identify any inflammation, including inflammation secondary to clozapine rapid titration.

Association between statin use and physical performance in home-dwelling older patients receiving polypharmacy: cross-sectional study.

BACKGROUND: In older patients with polypharmacy and multiple comorbidities, even low grades of statin-associated muscle symptoms may have clinical implications. The aim of this study was therefore to investigate the potential associations between statin use and measures of physical performance and muscle function. METHODS: Participants were aged 70+, treated with at least seven regular systemic medications, and not expected to die or become institutionalized within 6 months. Physical performance measured as gait speed and Short Physical Performance Battery (SPPB) score, and muscle function measured as grip strength, were compared between users and non-users of statins. In the subgroup of statin users, the dose-response relationship was assessed using harmonized simvastatin equivalents adjusted for statin potency, pharmacokinetic interactions and SLCO1B1 c.521 T > C genotype. Multiple linear regression analyses were applied to investigate potential associations between stain use and exposure as independent variables, and physical performance and muscle function as outcomes, adjusted for age, gender, body mass, comorbidity, disability and dementia. RESULTS: 174 patients (87 users and 87 non-users of statins) with a mean (SD) age of 83.3 (7.3) years were included. In analyses adjusted only for gender, grip strength was significantly higher in users than in non-users of statins [regression coefficient (B) 2.7, 95% confidence interval (CI) 1.0 to 4.4]. When adjusted for confounders, the association was no longer statistically significant (B 1.1, 95% CI - 0.5 to 2.7). SPPB and gait speed was also better in statin users than in non-users, but the differences were not statistically significant. In dose-response analyses adjusted for confounders, we found a statistically significant increase in SPPB score (B 0.01, 95% CI 0.00 to 0.02) and gait speed (B 0.001, 95% CI 0.000 to 0.002) per mg increase in simvastatin equivalents. CONCLUSIONS: In contrast to our hypothesis, statin use and exposure was associated with better measures of physical performance and muscle function in older patients with complex drug treatment. The unexpected findings of this cross-sectional, observational study should be further investigated by comparing physical performance before and after statin initiation or statin withdrawal in prospective studies. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02379455 , registered March 5, 2015.