Phenoconversion of CYP2D6 by inhibitors modifies aripiprazole exposure

Pharmacogenetics and phenoconversion: the influence on side effects experienced by psychiatric patients

Introduction: Preventing side effects is important to ensure optimal psychopharmacotherapy and therapeutic adherence among psychiatric patients. Obtaining the pharmacogenetic profile of CYP2C19 and CYP2D6 can play an important role in this. When the genotype-predicted phenotype shifts because of the use of co-medication, this is called phenoconversion. The aim was to study the influence of the pharmacogenetic (PGx) profile and phenoconversion on side effects experienced by psychiatric patients. Methods: A retrospective cohort study was performed using data from 117 patients from a psychiatric outpatient clinic. Patients were genotyped with a psychiatric PGx panel and side effects were evaluated using the Udvalg for Kliniske Undersølgelser side effects rating scale (UKU). Results: Of all patients, 10.3% and 9.4% underwent phenoconversion (any shift in predicted phenotype) for CYP2C19 and CYP2D6 respectively. No significant associations were found between the phenotype and UKU-score. 75% of the patients with an Intermediate metabolizer (IM) or Poor metabolizer (PM) phenoconverted phenotype of CYP2C19 experienced nausea and vomiting compared to 9.1% of the Normal metabolizer (NM) and Ultrarapid metabolizer (UM) patients (p = 0.033). 64% of the patients with an IM or PM phenoconverted phenotype of CYP2D6 experienced the side effect depression compared to 30.4% NMs and UMs (p = 0.020). CYP2D6 IM and PM patients had a higher concentration-dose ratio than NM patients (p < 0.05). Discussion: This study underlines the importance to consider phenoconversion when looking at a patient's genotype. This is important for a better prediction of the phenotype and preventing possible side effects under a specific psychopharmacotherapy.

Pharmacogenetics in the Treatment of Huntington’s Disease: Review and Future Perspectives

Huntington’s disease (HD) is an autosomal dominant progressive brain disorder, caused by a pathological expansion of a CAG repeat that encodes the huntingtin gene. This genetic neurodegenerative rare disease is characterized by cognitive, motor, and neuropsychiatric manifestations. The aim of the treatment is symptomatic and addresses the hyperkinetic disorders (chorea, dystonia, myoclonus, tics, etc.) and the behavioural and cognitive disturbances (depression, anxiety, psychosis, etc.) associated with the disease. HD is still a complex condition in need of innovative and efficient treatment. The long-term goal of pharmacogenetic studies is to use genotype data to predict the effective treatment response to a specific drug and, in turn, prevent potential undesirable effects of its administration. Chorea, depression, and psychotic symptoms have a substantial impact on HD patients’ quality of life and could be better controlled with the help of pharmacogenetic knowledge. We aimed to carry out a review of the available publications and evidence related to the pharmacogenetics of HD, with the objective of compiling all information that may be useful in optimizing drug administration. The impact of pharmacogenetic information on the response to antidepressants and antipsychotics is well documented in psychiatric patients, but this approach has not been investigated in HD patients. Future research should address several issues to ensure that pharmacogenetic clinical use is appropriately supported, feasible, and applicable.

[The relationship of cytochrome P450 isoforms with the efficacy and safety of antipsychotic and antidepressant therapy]

Cytochrome P450 (CYP450) is the leading enzyme in the biotransformation of most psychotropic drugs. CYP450 gene polymorphisms determine a patient's endophenotype with respect to the activity of enzymes of the family and affect the metabolism of prescribed antipsychotics and antidepressants. Categorizing patients by endophenotype during genotyping is likely to help simplify the selection of therapy in clinical practice. Co-prescribing drugs that may be inhibitors or inducers of CYP450 isoforms, in turn, may lead to adverse reactions or no effect of therapy. The article presents a compilation of known pharmacogenetic recommendations regarding the four major endophenotypes of metabolizers.

CYP2D6 pharmacogenetics and phenoconversion in personalized medicine

INTRODUCTION

CYP2D6 contributes to the metabolism of approximately 20-25% of drugs. However, CYP2D6 is highly polymorphic and different alleles can lead to impacts ranging from null to increase in activity. Moreover, there are commonly used drugs that potently inhibit the CYP2D6, thus causing 'phenoconversion' which can convert the genotypic normal metabolizer into phenotypic poor metabolizer. Despite growing literature on the clinical implications of non-normal CYP2D6 genotype and phenoconversion on patient-related outcomes, implementation of CYP2D6 pharmacogenetics and phenoconversion to guide prescribing is rare. This review focuses on providing the clinical importance of CYP2D6 pharmacogenetics and phenoconversion in precision medicine and summarizes the challenges and approaches to implement these into clinical practice.

AREAS COVERED

A literature search was performed using PubMed and clinical studies documenting the effects of CYP2D6 genotypes and/or CYP2D6 inhibitors on pharmacokinetics, pharmacodynamics or treatment outcomes of CYP2D6-metabolized drugs, and studies on implementation challenges and approaches.

EXPERT OPINION

Considering the extent and impact of genetic polymorphisms of CYP2D6, phenoconversion by the comedications, and contribution of CYP2D6 in drug metabolism, CYP2D6 pharmacogenetics is essential to ensure drug safety and efficacy. Utilization of proper guidelines incorporating both CYP2D6 pharmacogenetics and phenoconversion in clinical care assists in optimizing drug therapy.

The interplay between pharmacogenetics, concomitant drugs and blood levels of amitriptyline and its main metabolites

Background: The research considers the impact of genotype-inferred variability on blood levels of amitriptyline and its main metabolites, as may be moderated by phenocopying. Patients & methods: CYP2D6 and CYP2C19 genotypes, and serum concentrations of amitriptyline, nortriptyline and hydroxymetabolites, were determined in 33 outpatients. Co-medications were reviewed to identify CYP inhibition risk. Results: CYP2C19 metabolizer status explained interpatient variation in nortriptyline to amitriptyline concentration ratios. The hydroxymetabolite to parent ratios increased with higher CYP2D6 activity scores and lower CYP2D6 inhibition risk. In patients at high CYP2D6 inhibition risk, the amitriptyline + nortriptyline concentration was, on average, 52% above the higher end of expected ranges. Conclusion: Practical construal of pharmacogenetics and drug interactions tantamount to aberrant metabolism can facilitate patient-tailored use of the established drug.

CYP2D6 Genetic Variation and Antipsychotic-Induced Weight Gain: A Systematic Review and Meta-Analysis

BACKGROUND

Antipsychotic-induced weight gain is a contributing factor in the reduced life expectancy reported amongst people with psychotic disorders. CYP2D6 is a liver enzyme involved in the metabolism of many commonly used antipsychotic medications. We investigated if CYP2D6 genetic variation influenced weight or BMI among people taking antipsychotic treatment.

METHODS

We conducted a systematic review and a random effects meta-analysis of publications in Pubmed, Embase, PsychInfo, and CENTRAAL that had BMI and/or weight measurements of patients on long-term antipsychotics by their CYP2D6-defined metabolic groups (poor, intermediate, normal/extensive, and ultra-rapid metabolizers, UMs).

RESULTS

Twelve studies were included in the systematic review. All cohort studies suggested that the presence of reduced-function or non-functional alleles for CYP2D6 was associated with greater antipsychotic-induced weight gain, whereas most cross-sectional studies did not find any significant associations. Seventeen studies were included in the meta-analysis with clinical data of 2,041 patients, including 93 poor metabolizers (PMs), 633 intermediate metabolizers (IMs), 1,272 normal metabolizers (NMs), and 30 UMs. Overall, we did not find associations in any of the comparisons made. The estimated pooled standardized differences for the following comparisons were (i) PM versus NM; weight = -0.07 (95%CI: -0.49 to 0.35, p = 0.74), BMI = 0.40 (95%CI: -0.19 to 0.99, p = 0.19). (ii) IM versus NM; weight = 0.09 (95% CI: -0.04 to 0.22, p = 0.16) and BMI = 0.09 (95% CI: -0.24 to 0.41, p = 0.60). (iii) UM versus EM; weight = 0.01 (95% CI: -0.37 to 0.40, p = 0.94) and BMI = -0.08 (95%CI: -0.57 to 0.42, p = 0.77).

CONCLUSION

Our systematic review of cohort studies suggested that CYP2D6 poor metabolizers have higher BMI than normal metabolizers, but the data of cross-sectional studies and the meta-analysis did not show this association. Although our review and meta-analysis constitutes one of the largest studies with comprehensively genotyped samples, the literature is still limited by small numbers of participants with genetic variants resulting in poor or UMs status. We need further studies with larger numbers of extreme metabolizers to establish its clinical utility in antipsychotic treatment. CYP2D6 is a key gene for personalized prescribing in mental health.

CYP2D6 Genotyping and Antipsychotic-Associated Extrapyramidal Adverse Effects in a Randomized Trial of Aripiprazole Versus Quetiapine Extended Release in Children and Adolescents, Aged 12-17 Years, With First Episode Psychosis

PURPOSE/BACKGROUND

The aim of this study was to examine the association between genetically predicted CYP2D6 phenotypes and extrapyramidal symptoms (EPSs).

METHODS/PROCEDURES

Data from the Tolerability and Efficacy of Antipsychotics trial of adolescents with first-episode psychosis randomized to aripiprazole versus quetiapine extended release were studied. Extrapyramidal symptom assessments included the Simpson-Angus Scale and the Barnes Akathisia Rating Scale. Patients were CYP2D6 genotyped. Plasma concentrations of antipsychotics and antidepressants were analyzed.

FINDINGS/RESULTS

One hundred thirteen youths (age, 12-17 years; males, 30%; antipsychotic naive, 51%) were enrolled. Poor metabolizers had a significantly higher dose-adjusted aripiprazole plasma concentration (±SD) compared with normal metabolizers at week 4 (24.30 ± 6.40 ng/mL per milligram vs 14.85 ± 6.15 ng/mL per milligram; P = 0.019), but not at week 12 (22.15 ± 11.04 ng/mL per milligram vs 14.32 ± 4.52 ng/mL per milligram; P = 0.067). This association was not found in the quetiapine extended release group. No association between CYP2D6 genotype groups and global Barnes Akathisia Rating Scale score or Simpson-Angus Scale score was found in any of the treatment arms.

IMPLICATIONS/CONCLUSIONS

Our results do not support routine use of CYP2D6 testing as a predictor of drug-induced parkinsonism or akathisia risk in clinical settings. Further studies with larger samples of CYP2D6 poor metabolizers are needed.

Review: Influence of the CYP450 Genetic Variation on the Treatment of Psychotic Disorders

Second-generation antipsychotic metabolism is mainly carried out by the CYP450 superfamily, which is highly polymorphic. Therefore, knowing the influence of the different known CYP450 polymorphisms on antipsychotic plasmatic levels and, consequently, the biological effect could contribute to a deeper knowledge of interindividual antipsychotic treatment variability, prompting possible solutions. Considering this, this state of the art review aimed to summarize the current knowledge about the influence of the diverse characterized phenotypes on the metabolism of the most used second-generation antipsychotics. Forty studies describing different single nucleotide polymorphisms (SNPs) associated with the genes CYP1A2, CYP2D6, CYP3A4, CYP3A5, and ABCB1 and their influence on pharmacokinetics of olanzapine, clozapine, aripiprazole, risperidone, and quetiapine. Most of the authors concluded that although significant differences in the pharmacokinetic parameters between the different phenotypes could be observed, more thorough studies describing pharmacokinetic interactions and environmental conditions, among other variables, are needed to fully comprehend these pharmacogenetic interactions.

Partial agonists of dopamine receptors: mechanisms and clinical effects of aripiprazole, brexpiprazole and cariprazine

Aripiprazole, brexpiprazole and cariprazine are partial dopamine (and serotonin) agonists developed as novel antipsychotics. This article discusses their pharmacology, evidence on their licensed and off-licence uses (including psychosis, mania, bipolar depression, Tourette syndrome and autism spectrum disorder) and side-effects. In schizophrenia, they have a low risk of Parkinsonism or hyperprolactinaemia, cause modest increases in body weight and are of moderate efficacy.

How to Integrate CYP2D6 Phenoconversion Into Clinical Pharmacogenetics: A Tutorial

CYP2D6 genotype is increasingly being integrated into practice to guide prescribing of certain medications. The CYP2D6 drug metabolizing enzyme is susceptible to inhibition by concomitant drugs, which can lead to a clinical phenotype that is different from the genotype-based phenotype, a process referred to as phenoconversion. Phenoconversion is highly prevalent but not widely integrated into practice because of either limited experience on how to integrate or lack of knowledge that it has occurred. We built a calculator tool to help clinicians integrate a standardized method of assessing CYP2D6 phenoconversion into practice. During tool-building, we identified several clinical factors that need to be considered when implementing CYP2D6 phenoconversion into clinical practice. This tutorial shares the steps that the University of Florida Health Precision Medicine Program took to build the calculator tool and identified clinical factors to consider when implementing CYP2D6 phenoconversion in clinical practice.

Infection is associated with elevated serum concentrations of antipsychotic drugs

We aimed to investigate the effects of infection on serum concentrations of different antipsychotics in inpatients with respiratory tract infections treated with psychiatric drugs, including risperidone, clozapine, quetiapine, and aripiprazole. All patients underwent therapeutic drug monitoring (TDM) and routine blood tests during infection and noninfection periods. The Wilcoxon signed-rank test was used to analyze intra-individual differences in dose-corrected serum concentrations (C/D) levels in infection and noninfection periods. To study the effects of infection intensity on drug concentrations, white blood cells (WBCs) parameters and C/D levels were analyzed by Spearman's correlation analysis using all samples. The median C/D levels of risperidone (risperidone + 9-OH, n = 36) and clozapine (n = 42) were significantly higher (P < 0.001), whereas the median C/D levels of quetiapine (n = 21) and aripiprazole (n = 13) were slightly significantly higher (P < 0.01) in infection than in noninfection period. A significant positive association between C/D levels and WBC parameters was observed for risperidone, clozapine, and quetiapine. These results indicated reduced clearance of all drugs evaluated, especially clozapine and risperidone, due to infection. Therefore, during infection in patients receiving risperidone, clozapine, quetiapine, or aripiprazole, TDM should be performed to minimize the possible adverse effects associated with elevated drug concentrations.

Pharmacogenetic Testing of Cytochrome P450 Drug Metabolizing Enzymes in a Case Series of Patients with Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is associated with co-morbid psychiatric symptoms (disruptive behavior, anxiety, mood disorders, and psychosis) often requiring psychotropic medications. In this clinical case series of 35 patients with PWS, pharmacogenetic testing was obtained to determine allele frequencies predicting variations in activity of cytochrome (CYP) P450 drug metabolizing enzymes 2D6, 2B6, 2C19, 2C9, 3A4, and 1A2. Results were deidentified, collated, and analyzed by PWS genetic subtype: 14 deletion (DEL), 16 maternal uniparental disomy (UPD) and 5 DNA-methylation positive unspecified molecular subtype (PWS Unspec). Literature review informed comparative population frequencies of CYP polymorphisms, phenotypes, and substrate specificity. Among the total PWS cohort, extensive metabolizer (EM) activity prevailed across all cytochromes except CYP1A2, which showed greater ultra-rapid metabolizer (UM) status (p < 0.05), especially among UPD. Among PWS genetic subtypes, there were statistically significant differences in metabolizing status for cytochromes 2D6, 2C19, 2C9, 3A4 and 1A2 acting on substrates such as fluoxetine, risperidone, sertraline, modafinil, aripiprazole, citalopram, and escitalopram. Gonadal steroid therapy may further impact metabolism of 2C19, 2C9, 3A4 and 1A2 substrates. The status of growth hormone treatment may affect CYP3A4 activity with gender specificity. Pharmacogenetic testing together with PWS genetic subtyping may inform psychotropic medication dosing parameters and risk for adverse events.

Phenoconversion of Cytochrome P450 Metabolism: A Systematic Review

Phenoconversion is the mismatch between the individual’s genotype-based prediction of drug metabolism and the true capacity to metabolize drugs due to nongenetic factors. While the concept of phenoconversion has been described in narrative reviews, no systematic review is available. A systematic review was conducted to investigate factors contributing to phenoconversion and the impact on cytochrome P450 metabolism. Twenty-seven studies met the inclusion criteria and were incorporated in this review, of which 14 demonstrate phenoconversion for a specific genotype group. Phenoconversion into a lower metabolizer phenotype was reported for concomitant use of CYP450-inhibiting drugs, increasing age, cancer, and inflammation. Phenoconversion into a higher metabolizer phenotype was reported for concomitant use of CYP450 inducers and smoking. Moreover, alcohol, pregnancy, and vitamin D exposure are factors where study data suggested phenoconversion. The studies reported genotype–phenotype discrepancies, but the impact of phenoconversion on the effectiveness and toxicity in the clinical setting remains unclear. In conclusion, phenoconversion is caused by both extrinsic factors and patient- and disease-related factors. The mechanism(s) behind and the extent to which CYP450 metabolism is affected remain unexplored. If studied more comprehensively, accounting for phenoconversion may help to improve our ability to predict the individual CYP450 metabolism and personalize drug treatment.

Propranolol is a mechanism-based inhibitor of CYP2D and CYP2D6 in humanized CYP2D6-transgenic mice: Effects on activity and drug responses

BACKGROUND AND PURPOSE

Genetics and drug interactions contribute to large interindividual variation in human CYP2D6 activity. Here, we have characterized propranolol inhibition of human and mouse CYP2D using transgenic (TG) mice, which express both mouse CYP2D and human CYP2D6, and wild-type (WT) mice. Our purpose was to develop a method for in vivo manipulation of CYP2D6 enzyme activity which could be used to investigate the role of CYP2D6 in drug-induced behaviours.

EXPERIMENTAL APPROACH

Dextromethorphan metabolism to dextrorphan was used to measure CYP2D activity and to characterize propranolol inhibition in vitro and in vivo. Effects of propranolol pretreatment (24 hr) on serum levels of the CYP2D6 substrate haloperidol and haloperidol-induced catalepsy were also studied.

KEY RESULTS

Dextrorphan formation velocity in vitro was threefold higher in liver microsomes of TG compared to WT mice. Propranolol acted as a mechanism-based inhibitor (MBI), inactivating CYP2D in liver microsomes from TG and WT mice, and humans. Pretreatment (24 hr) of TG and WT mice with 20 mg·kg^-1 intraperitoneal propranolol reduced dextrorphan formation in vivo and by liver microsomes in vitro. Serum haloperidol levels and catalepsy were increased.

CONCLUSIONS AND IMPLICATIONS

Propranolol was a potent MBI of dextrorphan formation in liver microsomes from TG and WT mice, and humans. The inhibition parameters in TG overlapped with those in WT mice and in humans. Inhibition of CYP2D with propranolol in vivo in TG and WT mice altered drug responses, allowing further investigation of variations in CYP2D6 on drug interactions and drug responses.

Multi-site investigation of strategies for the clinical implementation of CYP2D6 genotyping to guide drug prescribing

Purpose:

A number of institutions have clinically implemented CYP2D6 genotyping to guide drug prescribing. We compared implementation strategies of early adopters of CYP2D6 testing, barriers faced by both early adopters and institutions in the process of implementing CYP2D6 testing, and approaches taken to overcome these barriers.

Methods:

We surveyed eight early adopters of CYP2D6 genotyping and eight institutions in the process of adoption. Data were collected on testing approaches, return of results procedures, applications of genotype results, challenges faced, and lessons learned.

Results:

Among early adopters, CYP2D6 testing was most commonly ordered to assist with opioid and antidepressant prescribing. Key differences among programs included test ordering and genotyping approaches, result reporting, and clinical decision support. However, all sites tested for copy number variation and 9 common variants, and reported results in the medical record. Most sites provided automatic consultation and had designated personnel to assist with genotype-informed therapy recommendations. Primary challenges were related to stakeholder support, CYP2D6 gene complexity, phenotype assignment, and sustainability.

Conclusion:

There are specific challenges unique to CYP2D6 testing given the complexity of the gene and its relevance to multiple medications. Consensus lessons learned may guide those interested in pursuing similar clinical pharmacogenetic programs.