Effects of CYP2D6 genotype on the pharmacokinetics, pharmacodynamics, and safety of risperidone in healthy volunteers

Influence of CYP2C19 and CYP2D6 on side effects of aripiprazole and risperidone: A systematic review

Variability in hepatic cytochrome P450 (CYP) enzymes such as 2C19 and 2D6 may influence side-effect and efficacy outcomes for antipsychotics. Aripiprazole and risperidone are two commonly prescribed antipsychotics, metabolized primarily through CYP2D6. Here, we aimed to provide an overview of the effect of CYP2C19 and CYP2D6 on side-effects of aripiprazole and risperidone, and expand on existing literature by critically examining methodological issues associated with pharmacogenetic studies. A PRISMA compliant search of six electronic databases (Pubmed, PsychInfo, Embase, Central, Web of Science, and Google Scholar) identified pharmacogenetic studies on aripiprazole and risperidone. 2007 publications were first identified, of which 34 were included. Quality of literature was estimated using Newcastle-Ottowa Quality Assessment Scale (NOS) and revised Cochrane Risk of Bias tool. The average NOS score was 5.8 (range: 3-8) for risperidone literature and 5 for aripiprazole (range: 4-6). All RCTs on aripiprazole were rated as high risk of bias, and four out of six for risperidone literature. Study populations ranged from healthy volunteers to inpatient individuals in psychiatric units and included adult and pediatric samples. All n = 34 studies examined CYP2D6. Only one study genotyped for CYP2C19 and found a positive association with neurological side-effects of risperidone. Most studies did not report any relationship between CYP2D6 and any side-effect outcome. Heterogeneity between and within studies limited the ability to synthesize data and draw definitive conclusions. Studies lacked statistical power due to small sample size, selective genotyping methods, and study design. Large-scale randomized trials with multiple measurements, providing robust evidence on this topic, are suggested.

Exploratory focused pharmacogenetic testing reveals novel markers associated with risperidone pharmacokinetics in Saudi children with autism

Background: Autism spectrum disorders (ASDs) encompass a broad range of phenotypes characterized by diverse neurological alterations. Genomic studies have revealed considerable overlap between the molecular mechanisms implicated in the etiology of ASD and genes involved in the pharmacokinetic (PK) and pharmacodynamic (PD) pathways of antipsychotic drugs employed in ASD management. Given the conflicting data originating from candidate PK or PD gene association studies in diverse ethnogeographic ASD populations, dosage individualization based on "actionable" pharmacogenetic (PGx) markers has limited application in clinical practice. Additionally, off-label use of different antipsychotics is an ongoing practice, which is justified given the shortage of approved cures, despite the lack of satisfactory evidence for its safety according to precision medicine. This exploratory study aimed to identify PGx markers predictive of risperidone (RIS) exposure in autistic Saudi children. Methods: This prospective cohort study enrolled 89 Saudi children with ASD treated with RIS-based antipsychotic therapy. Plasma levels of RIS and 9-OH-RIS were measured using a liquid chromatography-tandem mass spectrometry system. To enable focused exploratory testing, genotyping was performed with the Axiom PharmacoFocus Array, which included a collection of probe sets targeting PK/PD genes. A total of 720 PGx markers were included in the association analysis. Results: A total of 27 PGx variants were found to have a prominent impact on various RIS PK parameters; most were not located within the genes involved in the classical RIS PK pathway. Specifically, 8 markers in 7 genes were identified as the PGx markers with the strongest impact on RIS levels (p < 0.01). Four PGx variants in 3 genes were strongly associated with 9-OH-RIS levels, while 5 markers in 5 different genes explained the interindividual variability in the total active moiety. Notably, 6 CYP2D6 variants exhibited strong linkage disequilibrium; however, they significantly influenced only the metabolic ratio and had no considerable effects on the individual estimates of RIS, 9-OH-RIS, or the total active moiety. After correction for multiple testing, rs78998153 in UGT2B17 (which is highly expressed in the brain) remained the most significant PGx marker positively adjusting the metabolic ratio. For the first time, certain human leukocyte antigen (HLA) markers were found to enhance various RIS exposure parameters, which reinforces the gut-brain axis theory of ASD etiology and its suggested inflammatory impacts on drug bioavailability through modulation of the brain, gastrointestinal tract and/or hepatic expression of metabolizing enzymes and transporters. Conclusion: Our hypothesis-generating approach identified a broad spectrum of PGx markers that interactively influence RIS exposure in ASD children, which indicated the need for further validation in population PK modeling studies to define polygenic scores for antipsychotic efficacy and safety, which could facilitate personalized therapeutic decision-making in this complex neurodevelopmental condition.

In Vivo Characterization of Perseris and Compositionally Equivalent Formulations

Perseris is asubcutaneous extended-release risperidone in situ forming implant (suspension) indicated for the treatment of adult schizophrenia. Owing to the release rate controlling polymer poly(lactide-co-glycolide) (PLGA), one injection of Perseris can deliver risperidone for one month, which significantly reduces the administration frequency and improves patient compliance. The PLGA and drug used in Perseris was previously identified through reverse engineering and two compositionally equivalent formulations (F-1 and F-2) showing similar in vitro drug release were developed. The current work focuses on in vivo exploration of Perseris and the developed compositionally equivalent formulations using a rabbit model and further evaluate the sameness of the developed formulations compared to Perseris. The in vivo pharmacokinetic (PK) profiles, drug absorption rate, phase separation rate, macro appearance, weight loss as well as the water uptake of the solidified drug depots at different time points were investigated and compared with the in vitro release data as well as with dog and human in vivo data available in literature. Results show that the rabbit PK profile of Perseris was relevant with those obtained from both the dog model and the clinical data, indicating that the rabbit model is appropriate for investigation of the in vivo performance of risperidone implants. Consistent with their similar in vitro drug release, the two compositionally equivalent formulations demonstrated similar PK profiles, drug absorption rates, weight loss and swelling in vivo compared to Perseris. Although the erosion mechanism appeared to be similar between in vitro and in vivo, there were in vitro-in vivo differences concerning the drug release kinetics, phase separation rates and swelling behavior. This work provides a comprehensive in vitro/in vivo understanding of Perseris and the developed compositionally equivalent formulations, which will be beneficial for future development of generic as well as novel PLGA in situ forming implant products.

Physiologically-based pharmacokinetic model to investigate the effect of pregnancy on risperidone and paliperidone pharmacokinetics: Application to a pregnant woman and her neonate

This study aimed to determine the effects of pregnancy and ontogeny on risperidone and paliperidone pharmacokinetics by assessing their serum concentrations in two subjects and constructing a customized physiologically-based pharmacokinetic (PBPK) model. Risperidone and paliperidone serum concentrations were determined in a pregnant woman and her newborn. PBPK models for risperidone and paliperidone in adults, pediatric, and pregnant populations were developed and verified using the Simcyp simulator. These models were then applied to our two subjects, generating their "virtual twins." Effects of pregnancy on both drugs were examined using models with fixed pharmacokinetic parameters. In the neonatal PBPK simulation, 10 different models for estimating the renal function of neonates were evaluated. Risperidone was not detected in the serum of both pregnant woman and her newborn. Maternal and neonatal serum paliperidone concentrations were between 2.05-3.80 and 0.82-1.03 ng/ml, respectively. Developed PBPK models accurately predicted paliperidone's pharmacokinetics, as shown by minimal bias and acceptable precision across populations. The individualized maternal model predicted all observed paliperidone concentrations within the 90% prediction interval. Fixed-parameter simulations showed that CYP2D6 activity largely affects risperidone and paliperidone pharmacokinetics during pregnancy. The Flanders metadata equation showed the lowest absolute bias (mean error: 22.3% ± 6.0%) and the greatest precision (root mean square error: 23.8%) in predicting paliperidone plasma concentration in the neonatal population. Our constructed PBPK model can predict risperidone and paliperidone pharmacokinetics in pregnant and neonatal populations, which could help with precision dosing using the PBPK model-informed approach in special populations.

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.

Physiologically Based Pharmacokinetic Modeling to Describe the CYP2D6 Activity Score-Dependent Metabolism of Paroxetine, Atomoxetine and Risperidone

The cytochrome P450 2D6 (CYP2D6) genotype is the single most important determinant of CYP2D6 activity as well as interindividual and interpopulation variability in CYP2D6 activity. Here, the CYP2D6 activity score provides an established tool to categorize the large number of CYP2D6 alleles by activity and facilitates the process of genotype-to-phenotype translation. Compared to the broad traditional phenotype categories, the CYP2D6 activity score additionally serves as a superior scale of CYP2D6 activity due to its finer graduation. Physiologically based pharmacokinetic (PBPK) models have been successfully used to describe and predict the activity score-dependent metabolism of CYP2D6 substrates. This study aimed to describe CYP2D6 drug–gene interactions (DGIs) of important CYP2D6 substrates paroxetine, atomoxetine and risperidone by developing a substrate-independent approach to model their activity score-dependent metabolism. The models were developed in PK-Sim^®, using a total of 57 plasma concentration–time profiles, and showed good performance, especially in DGI scenarios where 10/12, 5/5 and 7/7 of DGI AUC_last ratios and 9/12, 5/5 and 7/7 of DGI C_max ratios were within the prediction success limits. Finally, the models were used to predict their compound’s exposure for different CYP2D6 activity scores during steady state. Here, predicted DGI AUC_ss ratios were 3.4, 13.6 and 2.0 (poor metabolizers; activity score = 0) and 0.2, 0.5 and 0.95 (ultrarapid metabolizers; activity score = 3) for paroxetine, atomoxetine and risperidone active moiety (risperidone + 9-hydroxyrisperidone), respectively.

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.

Genetic Polymorphisms Associated With the Pharmacokinetics, Pharmacodynamics and Adverse Effects of Olanzapine, Aripiprazole and Risperidone

Olanzapine, aripiprazole and risperidone are atypical antipsychotics or neuroleptics widely used for schizophrenia treatment. They induce various adverse drug reactions depending on their mechanisms of action: metabolic effects, such as weight gain and alterations of glucose and lipid metabolism; hyperprolactinemia and extrapyramidal effects, such as tremor, akathisia, dystonia, anxiety and distress. In this review, we listed polymorphisms associated with individual response variability to olanzapine, aripiprazole and risperidone. Olanzapine is mainly metabolized by cytochrome P450 enzymes, CYP1A2 and CYP2D6, whereas aripiprazole and risperidone metabolism is mainly mediated by CYP2D6 and CYP3A4. Polymorphisms in these genes and other enzymes and transporters, such as enzymes from the uridine 5'-diphospho-glucuronosyltransferase (UGT) family and ATP-binding cassette sub-family B member 1 (ABCB1), are associated to differences in pharmacokinetics. The three antipsychotics act on dopamine and serotonin receptors, among others, and several studies found associations between polymorphisms in these genes and variations in the incidence of adverse effects and in the response to the drug. Since olanzapine is metabolized by CYP1A2, a lower starting dose should be considered in patients treated with fluvoxamine or other CYP1A2 inhibitors. Regarding aripiprazole, a reduced dose should be administered in CYP2D6 poor metabolizers (PMs). Additionally, a reduction to a quarter of the normal dose is recommended if the patient is treated with concomitant CYP3A4 inhibitors. Risperidone dosage should be reduced for CYP2D6 PMs and titrated for CYPD6 ultrarapid metabolizers (UMs). Moreover, risperidone dose should be evaluated when a CYP2D6, CYP3A4 or ABCB1 inhibitor is administered concomitantly.

Physiologically Based Pharmacokinetic Modelling to Describe the Pharmacokinetics of Risperidone and 9-Hydroxyrisperidone According to Cytochrome P450 2D6 Phenotypes

BACKGROUND AND OBJECTIVES

The genetic polymorphism of cytochrome P450 (CYP) 2D6 is characterized by an excessive impact on positive and adverse drug reactions to antipsychotics, such as risperidone. Consequently, the pharmacokinetics of the drug and metabolite can be substantially altered and exhibit a high variability between the different phenotypes. The goal of this study was to develop a physiologically based pharmacokinetic (PBPK) model considering the CYP2D6 genetic polymorphism for risperidone and 9-hydroxyrisperidone (9-OH-RIS) taking CYP3A4 into account. Additionally, risperidone dose adjustments, which would compensate for genetically caused differences in the plasma concentrations of the active moiety (sum of risperidone and 9-OH-RIS) were calculated.

METHODS

Based on available knowledge about risperidone, 9-OH-RIS, and relevant physiological changes according to different CYP2D6 phenotypes, several PBPK models were built. In addition, an initial model was further evaluated based on the plasma concentrations of risperidone and 9-OH-RIS from a single-dose study including 71 genotyped healthy volunteers treated with 1 mg of oral risperidone.

RESULTS

PBPK models were able to accurately describe risperidone exposure after single-dose administration, especially in the concentration range ≥ 1 µg/L, illustrated by a minimal bias and a good precision. About 90.3% of all weighted residuals versus observed plasma concentrations ≥ 1 µg/L were in the ± 30% range. The risperidone/9-OH-RIS ratio increased progressively according to reduced CYP2D6 activity, resulting in a mean ratio of 4.96 for poor metabolizers. Simulations demonstrate that dose adjustment of the drug by - 25% for poor metabolizers and by - 10% for intermediate metabolizers results in a similar exposure to that of extensive metabolizers. Conversely, the risperidone/9-OH-RIS ratio can be used to determine the phenotype of individuals.

CONCLUSION

PBPK modelling can provide a valuable tool to predict the pharmacokinetics of risperidone and 9-OH-RIS in healthy volunteers, according to the different CYP2D6 phenotypes taking CYP3A4 into account. These models are able to ultimately support decision-making regarding dose-optimization strategies, especially for subjects showing lower CYP2D6 activity.

Association of CYP2C19 and CYP2D6 Poor and Intermediate Metabolizer Status With Antidepressant and Antipsychotic Exposure: A Systematic Review and Meta-analysis

IMPORTANCE

Precise estimation of the drug metabolism capacity for individual patients is crucial for adequate dose personalization.

OBJECTIVE

To quantify the difference in the antipsychotic and antidepressant exposure among patients with genetically associated CYP2C19 and CYP2D6 poor (PM), intermediate (IM), and normal (NM) metabolizers.

DATA SOURCES

PubMed, Clinicaltrialsregister.eu, ClinicalTrials.gov, International Clinical Trials Registry Platform, and CENTRAL databases were screened for studies from January 1, 1990, to June 30, 2020, with no language restrictions.

STUDY SELECTION

Two independent reviewers performed study screening and assessed the following inclusion criteria: (1) appropriate CYP2C19 or CYP2D6 genotyping was performed, (2) genotype-based classification into CYP2C19 or CYP2D6 NM, IM, and PM categories was possible, and (3) 3 patients per metabolizer category were available.

DATA EXTRACTION AND SYNTHESIS

The Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines were followed for extracting data and quality, validity, and risk of bias assessments. A fixed-effects model was used for pooling the effect sizes of the included studies.

MAIN OUTCOMES AND MEASURES

Drug exposure was measured as (1) dose-normalized area under the plasma level (time) curve, (2) dose-normalized steady-state plasma level, or (3) reciprocal apparent total drug clearance. The ratio of means (RoM) was calculated by dividing the mean drug exposure for PM, IM, or pooled PM plus IM categories by the mean drug exposure for the NM category.

RESULTS

Based on the data derived from 94 unique studies and 8379 unique individuals, the most profound differences were observed in the patients treated with aripiprazole (CYP2D6 PM plus IM vs NM RoM, 1.48; 95% CI, 1.41-1.57; 12 studies; 1038 patients), haloperidol lactate (CYP2D6 PM vs NM RoM, 1.68; 95% CI, 1.40-2.02; 9 studies; 423 patients), risperidone (CYP2D6 PM plus IM vs NM RoM, 1.36; 95% CI, 1.28-1.44; 23 studies; 1492 patients), escitalopram oxalate (CYP2C19 PM vs NM, RoM, 2.63; 95% CI, 2.40-2.89; 4 studies; 1262 patients), and sertraline hydrochloride (CYP2C19 IM vs NM RoM, 1.38; 95% CI, 1.27-1.51; 3 studies; 917 patients). Exposure differences were also observed for clozapine, quetiapine fumarate, amitriptyline hydrochloride, mirtazapine, nortriptyline hydrochloride, fluoxetine hydrochloride, fluvoxamine maleate, paroxetine hydrochloride, and venlafaxine hydrochloride; however, these differences were marginal, ambiguous, or based on less than 3 independent studies.

CONCLUSIONS AND RELEVANCE

In this systematic review and meta-analysis, the association between CYP2C19/CYP2D6 genotype and drug levels of several psychiatric drugs was quantified with sufficient precision as to be useful as a scientific foundation for CYP2D6/CYP2C19 genotype-based dosing recommendations.

Application of a Pharmacogenetics-Based Precision Medicine Model (5SPM) to Psychotic Patients That Presented Poor Response to Neuroleptic Therapy

Antipsychotics are the keystone of the treatment of severe and prolonged mental disorders. However, there are many risks associated with these drugs and not all patients undergo full therapeutic profit from them. The application of the 5 Step Precision Medicine model(5SPM), based on the analysis of the pharmacogenetic profile of each patient, could be a helpful tool to solve many of the problematics traditionally associated with the neuroleptic treatment. In order to solve this question, a cohort of psychotic patients that showed poor clinical evolution was analyzed. After evaluating the relationship between the prescribed treatment and pharmacogenetic profile of each patient, a great number of pharmacological interactions and pharmacogenetical conflicts were found. After reconsidering the treatment of the conflictive cases, patients showed a substantial reduction on mean daily doses and polytherapy cases, which may cause less risk of adverse effects, greater adherence, and a reduction on economic costs.

CYP2D6 Genetic Polymorphisms and Risperidone Pharmacokinetics: A Systematic Review and Meta-analysis

BACKGROUND

Risperidone is a second-generation antipsychotic drug metabolized to an active metabolite, 9-hydroxyrisperidone, primarily by cytochrome P450 (CYP) 2D6 and to a lesser extent by CYP3A4. The extent to which drug metabolism genetics impacts risperidone and 9-hydroxyrisperidone exposure has not been clarified.

OBJECTIVE

A systematic review and meta-analysis evaluated the impact of genetically defined CYP2D6 function on risperidone pharmacokinetics applying a standardized genotype-phenotype translation system.

METHODS

A comprehensive electronic database search identified studies reporting relationships between genetically determined CYP2D6 metabolism and risperidone pharmacokinetic properties. The exposure of risperidone or active moiety (risperidone + 9-hydroxyrisperidone) was measured by dose-adjusted steady-state serum or plasma concentration or area under the concentration-time curve as primary outcomes. Subjects were assigned to CYP2D6 poor metabolizer, intermediate metabolizer, normal metabolizer, or ultrarapid metabolizer groups using a standardized genotype-phenotype translation method. Effect sizes between groups were pooled and stratified by single or multiple dosing regimens.

RESULTS

A total of 15 studies involving 2125 adult subjects were included in the meta-analysis. Following multiple-dose oral administration, compared with CYP2D6 normal metabolizers, the risperidone dose-adjusted steady-state serum/plasma concentration was 2.35-fold higher in intermediate metabolizers (95% confidence interval [CI] 1.77-3.13, p<0.0001) and 6.20-fold higher in poor metabolizers (95% CI 5.05-7.62, p<0.0001); the active moiety dose-adjusted steady-state concentration was 1.18-fold higher in intermediate metabolizers (95% CI 1.11-1.25, p<0.0001) and 1.44-fold higher in poor metabolizers (95% CI 1.23-1.69, p<0.0001). Higher area under the concentration-time curve of risperidone and active moiety was also found in single-dose studies.

CONCLUSION

Genetically defined impaired CYP2D6 activity is associated with increased exposure of both risperidone and risperidone + 9-hydroxyrisperidone in adults receiving oral formulations. Additional studies are needed to quantify the clinical impact of these relationships.

The effect of CYP2D6 variation on antipsychotic-induced hyperprolactinaemia: a systematic review and meta-analysis

Hyperprolactinemia is a known adverse drug reaction to antipsychotic treatment. Antipsychotic blood levels are influenced by cytochrome P450 enzymes, primarily CYP2D6. Variation in CYP450 genes may affect the risk of antipsychotic-induced hyperprolactinemia. We undertook a systematic review and meta-analysis to assess whether CYP2D6 functional genetic variants are associated with antipsychotic-induced hyperprolactinemia. The systematic review identified 16 relevant papers, seven of which were suitable for the meta-analysis (n = 303 participants including 134 extreme metabolisers). Participants were classified into four phenotype groups as poor, intermediate, extensive, and ultra-rapid metabolisers. A random effects meta-analysis was used and Cohen's d calculated as the effect size for each primary study. We found no significant differences in prolactin levels between CYP2D6 metabolic groups. Current evidence does not support using CYP2D6 genotyping to reduce risk of antipsychotic-induced hyperprolactinemia. However, statistical power is limited. Future studies with larger samples and including a range of prolactin-elevating drugs are needed.

Effects of aripiprazole on circadian prolactin secretion related to pharmacogenetics in healthy volunteers

Aripiprazole treatment in schizophrenic patients was previously associated with lower or normalized prolactin levels. Genetic variants in cytochrome P450 (CYP) (CYP2D6), dopamine receptor (DRD2, DRD3) and serotonin receptor (HTR2A, HTR2C) genes were previously associated with antipsychotic-induced hyperprolactinaemia. Our aim was to evaluate whether aripiprazole affects prolactin secretion and its relationship with pharmacogenetics. Thirty-one healthy volunteers receiving a 10-mg single oral dose of aripiprazole were genotyped for 12 polymorphisms in CYP2D6, DRD2, DRD3, HTR2A and HTR2C genes by qPCR. Aripiprazole and dehydro-aripiprazole plasma concentrations were measured by HPLC-MS/MS. Prolactin concentrations of the 31 volunteers taking aripiprazole and 12 volunteers receiving ibuprofen were determined by ELISA. Prolactin concentrations after ibuprofen intake were considered as control, since it is known to cause no effect. Prolactin concentrations were slightly higher in the aripiprazole group compared to the ibuprofen group. All prolactin pharmacokinetic parameters were higher in females than in males. CYP2D6 poor and intermediate metabolizers had notably higher prolactin C_max and AUC_0-12 than normal and ultrarapid metabolizers. The DRD3 rs6280 polymorphism affected prolactin levels: volunteers carrying Ser/Ser genotype had significantly lower prolactin levels than volunteers carrying the Gly allele. Furthermore, HTR2C rs3813929 C/C homozygotes had significantly lower prolactin levels than T allele carriers. Nevertheless, aripiprazole did increase prolactin levels compared to ibuprofen.

Metabolism of risperidone by CYP2D6 and the presence of drug-induced dopamine supersensitivity psychosis in patients with schizophrenia

High-dose antipsychotic(s) can induce dopamine supersensitivity psychosis in schizophrenia patients. The precise relationship between a drug's blood concentration and the occurrence of dopamine supersensitivity psychosis has not been established. We divided 36 patients with schizophrenia who had undergone treatment mainly with risperidone into two groups: one with normal metabolizing activity of CYP2D6 (n = 15), and the other with lower activity of its variant, CYP2D6*10 (n = 21). The patients' blood concentrations of risperidone and 9-OH-risperidone were measured, and we compared the occurrence of dopamine supersensitivity psychosis episodes between the groups. There was no significant difference in any concentration of risperidone, 9-OH-risperidone, or active moiety between the groups although the with-CYP2D6*10 group had greater variabilities of these parameters compared to the without-CYP2D6*10 group. There was a lower rate of dopamine supersensitivity psychosis episodes in the without-CYP2D6*10 group (4/15, 26.7%) compared to the with-CYP2D6*10 group (11/21, 52.4%), but the difference was not significant. Although our findings were negative, largely because of the small sample size, these results suggest that (1) patients with an impaired functional allele of CYP2D6 may have higher concentrations of risperidone and its active metabolite and that (2) these patients may experience more frequent dopamine supersensitivity psychosis episodes.

CYP2D6 genotype and adverse events to risperidone in children and adolescents

BACKGROUND

There are few and conflicting data on the role of cytochrome P450 2D6 (CYP2D6) polymorphisms in relation to risperidone adverse events (AEs) in children. This study assessed the association between CYP2D6 metabolizer status and risk for risperidone AEs in children.

METHODS

Children ≤18 years with at least 4 weeks of risperidone exposure were identified using BioVU, a de-identified DNA biobank linked to electronic health record data. The primary outcome of this study was AEs. After DNA sequencing, individuals were classified as CYP2D6 poor, intermediate, normal, or ultrarapid CYP2D6 metabolizers.

RESULTS

For analysis, the 257 individuals were grouped as poor/intermediate metabolizers (n = 33, 13%) and normal/ultrarapid metabolizers (n = 224, 87%). AEs were more common in poor/intermediate vs. normal/ultrarapid metabolizers (15/33, 46% vs. 61/224, 27%, P = 0.04). In multivariate analysis adjusting for age, sex, race, and initial dose, poor/intermediate metabolizers had increased AE risk (adjusted odds ratio 2.4, 95% confidence interval 1.1-5.1, P = 0.03).

CONCLUSION

Children with CYP2D6 poor or intermediate metabolizer phenotypes are at greater risk for risperidone AEs. Pre-prescription genotyping could identify this high-risk subset for an alternate therapy, risperidone dose reduction, and/or increased monitoring for AEs.

Optimization of maintenance therapy of Risperidone with CYP2D6 genetic polymorphisms through an extended translational framework-based prediction of target occupancies/clinical outcomes

Risperidone, one of the second-generation antipsychotics, can efficiently target dopamine D₂ and serotonin 5-HT_2A receptors. There actually exists significant implication of CYP2D6 genetic polymorphisms on the metabolic kinetics of risperidone, little is known about the extent of CYP2D6 impacting human D2 and 5-HT2A receptor occupancies as well as the clinical efficacy and efficacy in schizophrenia treatment. Here we assessed the influences of CYP2D6 gene polymorphisms on human target occupancies/clinical outcomes and optimized the maintenance therapy of risperidone. A translational framework, previously developed using in vitro and in vivo information in rats, was used as the basis for integrating the effects of CYP2D6 genetic polymorphisms on target occupancies and clinical outcomes. D₂ occupancy as a biomarker was related to Positive and Negative Syndrome Scale (PANSS) response and Simpson-Angus Scale (SAS). The population approach was applied to characterize pharmacokinetic and pharmacodynamic (PK/PD) profiles of risperidone. Non-compartment analysis method was performed to calculate the steady state PK/PD parameters of both risperidone and 9-hydroxyrisperidone. The predictive power of this extended translational framework was determined by comparing the predictions of target occupancies and clinical outcomes with the reported human values of risperidone at clinically suggested dosage of 4.0 mg/day. This extended translational framework was adequately used to predict human target occupancies and clinical outcomes. At the steady state, D₂ ROs were 75.8%, 79.3% and 86.0% for CYP2D6 poor metabolizer (PM), intermediate metabolizer (IM) and extensive metabolizer (EM), respectively; 5-HT_2A ROs were 96.4%, 97.2% and 98.4% for CYP2D6 PM, IM and EM, respectively; PANSS changes from placebo were -5.3, -7.7 and -11.3 for CYP2D6 PM, IM and EM, respectively; SAS changes from placebo were 0.13, 0.15 and 0.18 for CYP2D6 PM, IM and EM, respectively. The predictions of human D₂, 5-HT_2A RO, PANSS and SAS changes for risperidone with CYP2D6 genetic polymorphisms were well in line with the reported values in clinic. 5.0, 4.0 and 2.5 mg/day were the equivalent dosages of risperidone for CYP2D6 PM, IM and EM, respectively. The optimized maintenance therapy of risperidone was provided through the Three-Step method and the dosage range was 2.5-5.0 mg/day for three CYP2D6 gene groups in the present study. Taken together, our findings demonstrate that this extended translational framework not only differentiates the effects of CYP2D6 genetic polymorphisms on target occupancies and clinical outcomes, but also constitutes a scientific basis to optimize the maintenance therapy of neuropsychiatric patients in clinic.

Classics in Chemical Neuroscience: Risperidone

After the identification of the influence of serotonergic receptors in ameliorating the negative symptoms associated with schizophrenia, atypical antipsychotics were developed by incorporating dopamine and serotonin antagonism. Risperidone, sold under the trade name Risperdal, was the second atypical antipsychotic developed following clozapine but quickly became a first-line treatment for acute and chronic schizophrenia because of its preferential side effect profile. Despite initial Food and Drug Administration approval 25 years ago, risperidone continues to be a fundamental treatment for schizophrenia, bipolar I disorder, and autism-related irritability. It is on the World Health Organization's List of Essential Medicines for its balance of efficacy, safety, tolerability, and cost-effectiveness. In this review, we highlight the history and importance of risperidone as an atypical antipsychotic, in addition to its chemical synthesis, manufacturing, drug metabolism and pharmacokinetics, pharmacology, structure-activity relationship, indications, and adverse effects.

Prolactin levels: sex differences in the effects of risperidone, 9-hydroxyrisperidone levels, CYP2D6 and ABCB1 variants

AIM

The role of sex on the association of plasma prolactin levels with risperidone (R) and 9-hydroxyrisperidone (9-OHR) concentrations is investigated.

METHODS

Plasma R and prolactin concentrations, CYP2D6 and exon 21 and 26 ABCB1 gene variants were studied in 110 patients.

RESULTS

In females, a 1 ng/ml increase in R levels was associated with a significant 1.02% increase in prolactin levels. In males, a 1 ng/ml increase in 9-OHR levels was associated with a significant 1.18% increase in prolactin levels. ABCB1 haplotype 12 had significant but opposite effects in males and females. In the combined sample, 9-OHR, but not R levels had significant effects on prolactin levels.

CONCLUSION

Genes had sex-specific effects on risperidone-associated prolactin elevations.

Rats and rabbits as pharmacokinetic screening tools for long acting intramuscular depots: case study with paliperidone palmitate suspension

Development of prodrug of 9-hydroxyrisperidone (paliperidone) long-acting intramuscular injection has enabled delivery over four-week time period with improved compliance. The key aim of this work was to establish a reliable preclinical model which may potentially serve as a screening tool for judging the pharmacokinetics of paliperidone formulation(s) prior to human clinical work. Sparse sampling composite study was used in rats, (Wistar/Sprague-Dawley (SD; n = 10)) and a serial blood sampling study design was used in rabbits (n = 4). Animals received intramuscular injection of paliperidone palmitate in the thigh muscle at dose of 16 (rats) and 4.5 mg/kg (rabbits). Samples were drawn in rats (retro-orbital sinus) and rabbits (central ear artery) and were analysed for paliperidone using liquid chromatography-mass spectrometry/ mass spectrometry (LC-MS/MS) assay. The plasma data was subjected to pharmacokinetic analysis. Following intramuscular injection of depot formulation in Wistar/SD rats and rabbits, absorption of paliperidone was slow and gradual with median value of time to reach maximum concentration (T_max) occurring on day 7. The exposures (i.e. area under the curve (AUC; 0-28) days) were 18,597, 21,865 and 18,120 ng.h/mL, in Wistar, SD and rabbits, respectively. The clearance was slow and supported long half-life (8-10 days). Either one of the two models can serve as a research tool for establishing pharmacokinetics of paliperidone formulation(s).

Pharmacokinetics of CYP2C9, CYP2C19, and CYP2D6 substrates in healthy Chinese and European subjects

PURPOSE

The aim of this analysis is to compare the pharmacokinetics of drug substrates in healthy Chinese and European subjects of aligned CYP2C9, CYP2C19, or CYP2D6 enzyme activity, providing further insight into drivers of interethnic differences in pharmacokinetics.

METHODS

Following identification of appropriate drug substrates, a comprehensive and structured literature search was conducted to identify single-dose pharmacokinetic data in healthy Chinese or European subjects with reported CYP2C9, CYP2C19, or CYP2D6 activity (genotype or phenotype). The ratio of drug AUC in the Chinese and European subjects classified with aligned enzyme activity was calculated (ethnicity ratio (ER)).

RESULTS

For 22/25 drugs identified, the ERs calculated indicated no or only limited interethnic differences in exposure (<twofold) in Chinese and European subjects with aligned polymorphic enzyme activity. The interethnic differences observed can reflect differences across populations in additional determinants of pharmacokinetics, although the notable between study variation and change over time in methods used to assign enzyme activity may also be contributing factors. There was no association between drug substrate fraction metabolized (fm) for CYP2C9, CYP2C19, or CYP2D6 and the ERs calculated.

CONCLUSION

The spectrum of pharmacokinetic determinants for each drug substrate and their differences across ethnic groups must be considered on a case-by-case basis in addition to metabolism by CYP2C9, CYP2C19, or CYP2D6. This analysis has also highlighted the challenges which arise when comparing published datasets if consistent methods to assign polymorphic enzyme activity have not been used.

1846G>A polymorphism of CYP2D6 gene and extrapyramidal side effects during antipsychotic therapy among Russians and Tatars: a pilot study

BACKGROUND

Сytochrome P450 CYP2D6 activity affects antipsychotic therapy safety. 1846G>A (CYP2D6*4) polymorphism frequency varies among different ethnic groups.

METHODS

We studied 1846G>A polymorphism in Tatar and Russian schizophrenic patients taking different antipsychotics and association of 1846G>A polymorphism and extrapyramidal disorders (EPD) frequency in schizophrenic patients on haloperidol monotherapy in daily doses up to 20 mg.

RESULTS

Heterozygous 1846GA genotype frequency among Tatars was lower (23.8% vs. 32.4% in Russians), but the differences did not reach statistical significance. The 1846A allele frequency among Tatars was also lower (11.9% vs. 24.3% in Russians), but the difference was not quite significant (p=0.0592). Average daily haloperidol dose in the group without EPD was significantly higher than in the group with EPD (11.35±4.6 vs. 13.87±3.3 mg, p=0.0252), but average daily haloperidol dose/weight ratios in the compared groups had no significant differences. A statistically significant association between EPD development and heterozygous 1846GA genotype and 1846A allele carrier frequency was revealed among all schizophrenic patients and among those of Tatars.

CONCLUSIONS

Further well-designed pharmacogenetic studies in different Russian regions are needed to improve psychotropic therapy safety and to establish evidence-based indications for pharmacogenetic testing in clinical practice.

Clinical Pharmacogenetics of Cytochrome P450-Associated Drugs in Children

Cytochrome P450 (CYP) enzymes are commonly involved in drug metabolism, and genetic variation in the genes encoding CYPs are associated with variable drug response. While genotype-guided therapy has been clinically implemented in adults, these associations are less well established for pediatric patients. In order to understand the frequency of pediatric exposures to drugs with known CYP interactions, we compiled all actionable drug-CYP interactions with a high level of evidence using Clinical Pharmacogenomic Implementation Consortium (CPIC) data and surveyed 10 years of electronic health records (EHR) data for the number of children exposed to CYP-associated drugs. Subsequently, we performed a focused literature review for drugs commonly used in pediatrics, defined as more than 5000 pediatric patients exposed in the decade-long EHR cohort. There were 48 drug-CYP interactions with a high level of evidence in the CPIC database. Of those, only 10 drugs were commonly used in children (ondansetron, oxycodone, codeine, omeprazole, lansoprazole, sertraline, amitriptyline, citalopram, escitalopram, and risperidone). For these drugs, reports of the drug-CYP interaction in cohorts including children were sparse. There are adequate data for implementation of genotype-guided therapy for children for three of the 10 commonly used drugs (codeine, omeprazole and lansoprazole). For the majority of commonly used drugs with known CYP interactions, more data are required to support pharmacogenomic implementation in children.

Investigation of the effect of solubility increase at the main absorption site on bioavailability of BCS class II drug (risperidone) using liquisolid technique

BCS class II drugs usually suffer inadequate bioavailability as dissolution step is the absorption rate limiting step. In this work, the effect of solubility increase at the main absorption site for these drugs was investigated using risperidone as a drug model. Liquisolid technique was applied to prepare risperidone per-oral tablets of high dissolution rate at intestinal pH (6.8) using versatile nonionic surfactants of high solubilizing ability [Transcutol HP, Labrasol and Labrasol/Labrafil (1:1) mixture] as liquid vehicles at different drug concentrations (10-30%) and fixed (R). The prepared liquisolid tablets were fully evaluated and the dissolution rate at pH 6.8 was investigated. The formulae that showed significantly different release rate were selected and subjected to mathematical modeling using DE25, MDT and similarity factor (f2). Depending on mathematical modeling results, formula of higher dissolution rate was subjected to solid state characterization using differential scanning calorimetric (DSC), infrared spectroscopy (IR) and X-ray diffraction (XRD). Finally, the drug bioavailability was studied in comparison to conventional tablets in rabbits. Results showed that liquisolid tablet prepared using Labrasol/Labrafil (1:1) mixture as liquid vehicle containing 10% risperidone is a compatible formula with law drug crystallinity and higher dissolution rate (100% in 25 min). The drug bioavailability was significantly increased in comparison to the conventional tablets (1441.711 μg h/mL and 137.518 μg/mL in comparison to 321.011 μg h/mL and 38.673 μg/mL for AUC and Cpmax, respectively). This led to the conclusion that liquisolid technique was efficiently improved drug solubility and solubility increase of BCS class II drugs at their main absorption site significantly increases their bioavailability.

Physicochemical properties of dietary phytochemicals can predict their passive absorption in the human small intestine

A diet high in phytochemical-rich plant foods is associated with reducing the risk of chronic diseases such as cardiovascular and neurodegenerative diseases, obesity, diabetes and cancer. Oxidative stress and inflammation (OSI) is the common component underlying these chronic diseases. Whilst the positive health effects of phytochemicals and their metabolites have been demonstrated to regulate OSI, the timing and absorption for best effect is not well understood. We developed a model to predict the time to achieve maximal plasma concentration (Tmax) of phytochemicals in fruits and vegetables. We used a training dataset containing 67 dietary phytochemicals from 31 clinical studies to develop the model and validated the model using three independent datasets comprising a total of 108 dietary phytochemicals and 98 pharmaceutical compounds. The developed model based on dietary intake forms and the physicochemical properties lipophilicity and molecular mass accurately predicts Tmax of dietary phytochemicals and pharmaceutical compounds over a broad range of chemical classes. This is the first direct model to predict Tmax of dietary phytochemicals in the human body. The model informs the clinical dosing frequency for optimising uptake and sustained presence of dietary phytochemicals in circulation, to maximise their bio-efficacy for positively affect human health and managing OSI in chronic diseases.

Pharmacogenetics of Risperidone: A Systematic Review of the Clinical Effects of CYP2D6 Polymorphisms

OBJECTIVE

To summarize and evaluate the pharmacogenetic literature pertaining to the effects of CYP2D6 polymorphism on clinical outcomes of risperidone therapy.

DATA SOURCES

A systematic literature search was performed using the search terms risperidone, pharmacogenetics, cytochrome P-450 enzyme system, cytochrome P-450 CYP2D6, and polymorphism (genetic) in MEDLINE (1946-October 2012), EMBASE (1980-October 2012), PubMed (1947-October 2012), International Pharmaceutical Abstracts (1970-October 2012), and Google Scholar.

STUDY SELECTION AND DATA EXTRACTION

Identified articles were included if they measured the association between CYP2D6 genetic polymorphisms and clinical outcomes in at least 2 patients taking risperidone. The data elements extracted from these articles consisted of study design, number of subjects, indication for risperidone therapy, CYP2D6 phenotype status, mean daily dose of risperidone, and effects on clinical outcomes.

DATA SYNTHESIS

The identified citations consisted of 10 prospective nonrandomized, uncontrolled cohort studies, 1 retrospective cohort study, 1 prospective case-control study, and 1 retrospective case series. Studies were of variable quality and none provided high-quality evidence; they included heterogeneous patient populations with varying clinical diagnoses and drug therapy regimens. Most studies reported nonsignificant trends but were limited by power to detect statistical significance and short trial duration. However, increased risk of adverse effects (including QT interval prolongation) was observed in patients with inactive alleles.

CONCLUSIONS

While there were trends toward increased adverse effects in poor metabolizers, most outcomes were not significant. As such, routine genotyping should not be used for screening. Future usefulness cannot be ruled out, as many studies had significant limitations that preclude determination of clinical relevance. Adequately powered clinical and epidemiologic studies are warranted to clarify the role of CYP2D6 genotyping in practice.

CYP2D6 polymorphisms and their influence on risperidone treatment

Cytochrome P450 enzyme especially CYP2D6 plays a major role in biotransformation. The interindividual variations of treatment response and toxicity are influenced by the polymorphisms of this enzyme. This review emphasizes the effect of CYP2D6 polymorphisms in risperidone treatment in terms of basic knowledge, pharmacogenetics, effectiveness, adverse events, and clinical practice. Although the previous studies showed different results, the effective responses in risperidone treatment depend on the CYP2D6 polymorphisms. Several studies suggested that CYP2D6 polymorphisms were associated with plasma concentration of risperidone, 9-hydroxyrisperidone, and active moiety but did not impact on clinical outcomes. In addition, CYP2D6 poor metabolizer showed more serious adverse events such as weight gain and prolactin than other predicted phenotype groups. The knowledge of pharmacogenomics of CYP2D6 in risperidone treatment is increasing, and it can be used for the development of personalized medication in term of genetic-based dose recommendation. Moreover, the effects of many factors in risperidone treatment are still being investigated. Both the CYP2D6 genotyping and therapeutic drug monitoring are the important steps to complement the genetic-based risperidone treatment.

Impact of Pharmacogenetic Markers of CYP2D6 and DRD2 on Prolactin Response in Risperidone-Treated Thai Children and Adolescents With Autism Spectrum Disorders

OBJECTIVE

The aim of the study was to identify the impact of pharmacogenetic markers associated with prolactin concentration in risperidone-treated children and adolescents with autism spectrum disorders.

METHODS

One hundred forty-seven children and adolescents with autism, aged 3 to 19 years, received risperidone. The clinical data of patients were recorded from medical records. Prolactin levels were measured by chemiluminescence immunoassay. Three CYP2D6 single nucleotide polymorphisms, CYP2D6*4 (1846G>A), *10 (100C>T), and *41 (2988G>A), 1 gene deletion (*5), and DRD2 Taq1A (rs1800497) polymorphism were genotyped by TaqMan real-time polymerase chain reaction.

RESULTS

The 3 common allelic frequencies were CYP2D6*10 (55.10%), *1 (32.65%), and *5 (6.12%), respectively. Patients were grouped according to their CYP2D6 genotypes. There was no significant correlation between the concentrations of prolactin among the CYP2D6 genotypes. In addition, there were no statistical differences in the prolactin response among the CYP2D6-predicted phenotypes of extensive metabolizer and intermediate metabolizer. The DRD2 genotype frequencies were Taq1A A2A2 (38.77%), A1A2 (41.50%), and A1A1 (19.73%), respectively. There were statistically significant differences in prolactin level of patients among the 3 groups (P = 0.033). The median prolactin level in patients with DRD2 Taq1A A2A2 (17.80 ng/mL) was significantly higher than A1A2 (17.10 ng/mL) and A1A1 (12.70 ng/mL).

CONCLUSIONS

DRD2 Taq1A A2A2 polymorphisms may play a significant role in the hyperprolactinemia- associated with risperidone treatment in children and adolescent with autism spectrum disorder. Many drugs used chronically in psychiatric diseases exert their effects mainly through the dopamine D2 receptor. It is therefore possible that these drugs could alter the expression of any dopamine receptor, thus affecting the pharmacodynamics characteristics and toxicity of drug substrates during pharmacotherapy.

Individual differences in in vitro and in vivo metabolic clearances of antipsychotic risperidone from Japanese subjects genotyped for cytochrome P450 2D6 and 3A5

OBJECTIVE

There are conflicting reports regarding the effects of cytochrome P450 (P450, CYP) genotypes on the plasma concentrations of risperidone and its pharmacologically active metabolite, 9-hydroxyrisperidone (paliperidone), in clinical patients. The aim of this study was to investigate individual differences in the metabolic clearance of risperidone in vitro and in vivo.

METHODS

In vitro liver microsomal risperidone 9-hydroxylation activities and in vivo plasma concentrations of risperidone and paliperidone were investigated in 15 male and 12 female Japanese subjects (mean age 52 years, range: 24-75 years) genotyped for CYP2D6 and CYP3A5.

RESULTS

CYP2D6 intermediate and poor metabolizers showed significantly lower liver microsomal risperidone 9-hydroxylation activities than extensive metabolizers did at 5 μM of risperidone; this difference was not evident at 50 μM of risperidone. The recombinant CYP3A5 Vmax/Km value for risperidone 9-hydroxylation was 30% that of CYP3A4, and liver microsomes from CYP3A5 expressers had similar risperidone 9-hydroxylation activities to those of CYP3A5 poor expressers. The plasma concentration/dose ratios for risperidone and paliperidone in 27 Japanese patients were not significantly influenced by the CYP2D6 or CYP3A5 genotypes.

CONCLUSIONS

Individual differences in metabolic clearance of risperidone under the present conditions were not significantly influenced by the genotypes of CYP2D6 or CYP3A5.

Detection of CYP2D6 polymorphism using Luminex xTAG technology in autism spectrum disorder: CYP2D6 activity score and its association with risperidone levels

CYP2D6 is involved in the biotransformation of a large number of drugs, including risperidone. This study was designed to detect CYP2D6 polymorphisms with a Luminex assay, including assessment the relationship of CYP2D6 polymorphisms and risperidone plasma concentration in autism spectrum disorder children (ASD) treated with risperidone. All 84 ASD patients included in this study had been receiving risperidone at least for 1 month. The CYP2D6 genotypes were determined by Luminex assay. Plasma concentrations of risperidone and 9-hydroxyrisperidone were measured using LC/MS/MS. Among the 84 patients, there were 46 (55.42%) classified as EM, 33 (39.76%) as IM, and 4(4.82%) as UM. The plasma concentration of risperidone and risperidone/9-hydroxyrisperidone ratio in the patients were significant differences among the CYP2D6 predicted phenotype group (P = 0.001 and P < 0.0001 respectively). Moreover, the plasma concentration of risperidone and risperidone/9-hydroxyrisperidone ratio in the patients with CYP2D6 activity score 0.5 were significantly higher than those with the CYP2D6 activity score 2.0 (P = 0.004 and P = 0.002 respectively). These findings suggested that the determination of the accurate CYP2D6 genotype-predicted phenotype is essential in the clinical setting and individualization of drug therapy. The use of the Luminex assay for detection of CYP2D6 polymorphisms could help us more accurately identify an individual's CYP2D6 phenotype.

Applicability of gene expression and systems biology to develop pharmacogenetic predictors; antipsychotic-induced extrapyramidal symptoms as an example

Pharmacogenetics has been driven by a candidate gene approach. The disadvantage of this approach is that is limited by our current understanding of the mechanisms by which drugs act. Gene expression could help to elucidate the molecular signatures of antipsychotic treatments searching for dysregulated molecular pathways and the relationships between gene products, especially protein-protein interactions. To embrace the complexity of drug response, machine learning methods could help to identify gene-gene interactions and develop pharmacogenetic predictors of drug response. The present review summarizes the applicability of the topics presented here (gene expression, network analysis and gene-gene interactions) in pharmacogenetics. In order to achieve this, we present an example of identifying genetic predictors of extrapyramidal symptoms induced by antipsychotic.

Risperidone-associated adverse drug reactions and CYP2D6 polymorphisms in a South African cohort

Background

Contradictory information exists regarding the influence of CYP2D6 polymorphisms on adverse drug reactions (ADRs) (extrapyramidal symptoms (EPS) and weight gain) related to risperidone treatment. This prompted us to evaluate the influence of CYP2D6 genetic variation in a cohort of South African patients who presented with marked movement disorders and/or weight gain while on risperidone treatment.

Methods

Patients who were experiencing marked risperidone ADRs were recruited from Weskoppies Public Psychiatric Hospital. As poor or intermediate metabolism was expected, comprehensive CYP2D6 sequence variations were evaluated using XL-PCR + Sequencing.

Results

No statistically significant association was found between CYP2D6 poor metabolism and risperidone ADRs. An inverse relationship between EPS and weight gain was however identified. A novel CYP2D6 allele was identified which is unlikely to affect metabolism based on in silico evaluation.

Conclusion

CYP2D6 variation appeared not to be a good pharmacogenetic marker for predicting risperidone-related ADRs in this naturalistic South African cohort. Evaluation of a larger cohort would be needed to confirm these observations, including an examination of the role of potential intermediaries between the hypothesised genetic and clinical phenotypes.

Pharmacogenetics of second-generation antipsychotics

This review considers pharmacogenetics of the so called 'second-generation' antipsychotics. Findings for polymorphisms replicating in more than one study are emphasized and compared and contrasted with larger-scale candidate gene studies and genome-wide association study analyses. Variants in three types of genes are discussed: pharmacokinetic genes associated with drug metabolism and disposition, pharmacodynamic genes encoding drug targets, and pharmacotypic genes impacting disease presentation and subtype. Among pharmacokinetic markers, CYP2D6 metabolizer phenotype has clear clinical significance, as it impacts dosing considerations for aripiprazole, iloperidone and risperidone, and variants of the ABCB1 gene hold promise as biomarkers for dosing for olanzapine and clozapine. Among pharmacodynamic variants, the TaqIA1 allele of the DRD2 gene, the DRD3 (Ser9Gly) polymorphism, and the HTR2C -759C/T polymorphism have emerged as potential biomarkers for response and/or side effects. However, large-scale candidate gene studies and genome-wide association studies indicate that pharmacotypic genes may ultimately prove to be the richest source of biomarkers for response and side effect profiles for second-generation antipsychotics.

Effect of polymorphisms on the pharmacokinetics, pharmacodynamics, and safety of risperidone in healthy volunteers

OBJECTIVE

To identify genetic markers capable of predicting the pharmacokinetics, pharmacodynamics, and adverse effects of risperidone.

METHODS

Genotyping was performed in 70 healthy volunteers receiving a single 1mg oral dose of risperidone. Risperidone and hydroxyrisperidone plasma levels were measured using high-performance liquid chromatography combined with tandem mass spectrometry.Prolactin concentration was quantified by direct chemiluminescence.

RESULTS

Poor CYP2D6 metabolizers showed higher risperidone Cmax, area under the curve (AUC), and t1/2, as well as lower clearance. They also showed lower Cmax and AUC and higher t1/2 for hydroxyrisperidone. Furthermore, individuals with a mutant VKORC1 genotype had a lower risperidone AUC and t1/2 and higher clearance. The hydroxyrisperidone AUC was lower in individuals with the COMT mutant genotype. Risperidone increased prolactin levels (iAUC and iCmax), which were higher in women than in men. The most frequent reactions were somnolence (47.1%), headache (21.4%), and dizziness (17.1%). Women had neurological effects and headache more frequently than men. The incidence of headache was associated with polymorphisms in the AGTR1 and NAT2; neurological effects were associated with CYP2C19.

CONCLUSIONS

Differences in the pharmacokinetics of risperidone are due to polymorphisms in CYP2D6, COMT, and VKORC1. Differences in adverse reactions can be explained by gender and polymorphisms in CYP2C19, AGTR1, and NAT2.

Polymorphisms in CYP2D6 have a greater effect on variability of risperidone pharmacokinetics than gender

Within-subject coefficient of variation (CVw ) plays a decisive role in the determination of sample size in bioequivalence clinical trials. Highly variable drugs may require the participation of a large number of subjects. The aim of this study was to investigate whether gender and polymorphisms in CYP2D6 affect the CVw of risperidone. Two single-dose, two-period crossover studies of risperidone (n = 70) were reanalysed to calculate CVw for AUCt and Cmax . Subjects were classified into four different CYP2D6 phenotype groups [poor metabolizers (PM), intermediate metabolizers (IM), extensive metabolizers (EM) and ultrarapid metabolizers (UM)]. The effect of gender was evaluated in EM and IM. CVw was lower in PM (13.3% for AUCt and 10.9% for Cmax ) and UM (17.4% and 8.7%) than in EM (28.7% and 34.7%) and IM (33.2% and 27.3%). Variability was slightly lower in women (27.9% for AUCt and 25.7% for Cmax ) than in men (33.3% and 37.2%, respectively). Genetic polymorphisms affect within-subject variability more than gender and could considerably affect sample size calculation. Therefore, subjects participating in bioequivalence trials should be genotyped.

Effect of CYP2D6 on risperidone pharmacokinetics and extrapyramidal symptoms in healthy volunteers: results from a pharmacogenetic clinical trial

AIM

To elucidate the relationship between CYP2D6 genotype and risperidone pharmacokinetics and extrapyramidal symptoms we propose the APSEP pharmacogenetic clinical trial.

MATERIALS & METHODS

Twenty-five healthy subjects were included in this randomized, placebo-controlled, single dose (risperidone 2.5 mg) crossover and double-blind clinical trial. Subjects were selected according to their CYP2D6 genotype and classified as: poor metabolizers (n = 8), extensive metabolizers (n = 10) and ultrarapid metabolizers (n = 7).

RESULTS & CONCLUSION

Our study demonstrates that CYP2D6 predicted 65% of the risperidone metabolism variability. Moreover, its ability to predict actigraphy records is similar to the predictive power of pharmacokinetic parameters (24%). Our results also highlight the need for the development of pharmacogenetic predictors that take into account the complexity of pharmacokinetic and pharmacodynamic relationships.

Effect of risperidone metabolism and P-glycoprotein gene polymorphism on QT interval in patients with schizophrenia

Risperidone (RIS) is a frequently used efficacious psychotropic drug. However, it prolongs the QTc interval and may cause fatal arrhythmia. Little is known on the determinants of this RIS side effect. RIS is metabolized by CYP2D6, and is subject to drug efflux by P-glycoprotein (P-gp) encoded by the ATP-binding cassette subfamily B member 1 (ABCB1) gene. P-gp removes both RIS and its metabolite 9-OH-RIS from cardiac tissue. To investigate the effect of RIS metabolism and ABCB1 gene polymorphisms on QTc, steady-state plasma RIS and 9-OH-RIS levels, and QTc were measured. CYP2D6, ABCB1 C3435T and G2677T/A genotypes were determined in 66 schizophrenia patients on RIS. QTc was significantly longer in patients with ABCB1 3435CT+3435 TT than in those with 3435CC (P=0.006). ABCB1 G2677T/A genotype did not affect QTc. Multiple regression analysis showed that C/T or T/T genotypes at the ABCB1 C3435T locus, lower weight, and older age prolonged QTc. In summary, the T allele of the ABCB1 C3435T genotype should be considered in future diagnostic development efforts for RIS-associated QT.

Pharmacokinetic behavior presents drug therapy challenges

There are conditions that cause a substantial change in drug clearance to such a degree that how a specific drug is managed to optimize drug response and minimize drug toxicity presents a challenge. This review will focus on recent literature (within the past 5 years) that evaluates pathophysiologic and genetic conditions and drug interactions which can change drug clearance to the magnitude that response is affected. Situations discussed that cause an increase in drug clearance will include: augmented renal clearance in critically ill patients; ultrafast drug metabolism caused by gene duplication; and enzyme induction interactions caused by rifampin. Situations discussed that result in a reduction in clearance will include: multiple organ failure in critically ill, patients with non-functioning CYP2D6 and CYP2C8/9 alleles, and CYP3A4 drug interactions with erythromycin and clarithromycin. In each case evaluated clearance is changed to the magnitude such that managing drug therapy can be difficult.

Towards the implementation of CYP2D6 and CYP2C19 genotypes in clinical practice: update and report from a pharmacogenetic service clinic

Genetic testing may help to improve treatment outcomes in order to avoid non-response or severe side effects to psychotropic medication. Most robust data have been obtained for gene variants in CYP2D6 and CYP2C19 enzymes for antipsychotics and antidepressant treatment. We reviewed original articles indexed in PubMed from 2008-2013 on CYP2D6 and CYP2C19 gene variants and treatment outcome to antidepressant or antipsychotic medication. We have started providing CYP2D6 and CYP2C19 genotype information to physicians and conducted a survey where preliminary results are reported. Studies provided mixed results regarding the impact of CYP2D6 and CYP2C19 gene variation on treatment response. Plasma levels were mostly found associated with CYP metabolizer status. Higher occurrence/severity of side effects were reported in non-extensive CYP2D6 or CYP2C19 metabolizers. Results showed that providing genotypic information is feasible and generally well accepted by both patients and physicians. Although currently available studies are limited by small sample sizes and infrequent plasma drug level assessment, research to date indicates that CYP2D6 and CYP2C19 testing may be beneficial particularly for non-extensive metabolizing patients. In summary, clinical assessment of CYP2D6 and CYP2C19 metabolizer status is feasible, well accepted and optimizes drug treatment in psychiatry.

An integrated clinical pharmacology approach for deriving dosing recommendations in a regulatory setting: review of recent cases in psychiatry drugs

Clinical pharmacology as an interdisciplinary science is unique in its capacity and the diversity of the methods and approaches it can provide to derive dosing recommendations in various subpopulations. This article illustrates cases where an integrated clinical pharmacology approach was used to derive dosing recommendations for psychiatry drugs within regulatory settings. The integrated approach is based on the view that once a drug is shown to be effective in the general population, it is reasonable to take into consideration other relevant findings and the use of alternative scientific tools and analysis to derive dosing recommendations in specific populations. The method provides useful means to solve the challenges of the paucity of available data and lead to clear dosing instructions. This in turn expands the benefits of any given drug to all individuals in which the drug is likely to be effective.

Pharmacodynamic genetic variants related to antipsychotic adverse reactions in healthy volunteers

Aim: Clinical trials with healthy volunteers are a useful model for evaluating safety and tolerability, without the interference of concomitant diseases and drugs. The present study aims to improve our understanding of antipsychotic-related adverse reactions (ARs) and their possible association with common genetic variants of pharmacodynamic proteins such as neurotransmitter receptors/transporters. Materials & methods: A total of eight polymorphisms located in seven pharmacodynamic-related genes (SCL6A4, MDR1, 5HT2A, DRD2, DRD3, COMT and GRIN2B) were genotyped in a cohort of 211 healthy volunteers who received a single dose of risperidone (1 mg), olanzapine (5 mg) or quetiapine (25 mg). Results: Interestingly, a significant association was found between the incidence of neurological ARs and specific polymorphisms in key genes (DRD2 and SCL6A4). Conclusion: Genetic variants in pharmacodynamic genes could represent valuable markers of AR risk and antipsychotic safety.

Original submitted 7 February 2013; Revision submitted 3 June 2013

Impact of the ABCB1 gene polymorphism on plasma 9-hydroxyrisperidone and active moiety levels in Japanese patients with schizophrenia

9-Hydroxyrisperidone (9-OH-RIS) is an active metabolite of the antipsychotic drug risperidone (RIS). The total active moiety level, in other words the sum of the RIS and 9-OH-RIS serum levels, may be important for estimating the clinical effects of RIS treatment. However, there have been no consistent results reported regarding the relationship between cytochrome P450 (CYP) 2D6 or adenosine triphosphate-binding cassette subfamily B member 1 (ABCB1) variant alleles and 9-OH-RIS or total active moiety plasma levels. Seventy-four Japanese patients treated with RIS were examined in the present study. Steady-state plasma RIS and 9-OH-RIS were measured. The CYP2D6*5, CYP2D6*10, ABCB1 3435C>T, and ABCB1 2677G>T/A genotypes were detected. Multiple regression analysis showed that the dose-corrected plasma RIS levels were significantly correlated with the number of CYP2D6 variant alleles and ABCB1 3435C>T genotypes, whereas the 9-OH-RIS and total active moiety levels were significantly correlated with the ABCB1 3435C>T genotypes and with age. On the other hand, the ABCB1 2677G>T/A genotypes did not affect plasma RIS, 9-OH-RIS, or total active moiety levels. The ABCB1 3435C>T genetic polymorphism may predict plasma 9-OH-RIS and total active moiety levels.

Population pharmacokinetic modeling of risperidone and 9-hydroxyrisperidone to estimate CYP2D6 subpopulations in children and adolescents

AIM

The study aims were to characterize risperidone and (±)-9-hydroxyrisperidone pharmacokinetic (PK) variability in children and adolescents and to evaluate covariate effects on PK parameters.

METHODS

Steady-state samples were drawn at predose, 1, 2, 4, and 7 hours postdose; cytochrome P450 2D6 (CYP2D6) genotypes were available for 28 subjects. A nonlinear mixed-effects model (NONMEM) modeled the PKs of risperidone and (±)-9-hydroxyrisperidone; covariates included age, weight, sex, and CYP2D6 phenotype. The model included 497 observations [risperidone (n = 163), (+) and (-)-9-hydroxyrisperidone (n = 334)] from 45 subjects aged 3-18.3 (mean 9.6 ± 3.7) years, weighing 16.8-110 (43 ± 20.2) kg.

RESULTS

A 1-compartment mixture model described risperidone and (±)-9-hydroxyrisperidone clearances for 3 CYP2D6 metabolizer subpopulations: extensive, intermediate, and poor. Weight significantly affected (±)-9-hydroxyrisperidone clearance. Clearance estimates in the mixture model were poor metabolizer 9.38 L/h, intermediate metabolizer 29.2 L/h, and extensive metabolizer 37.4 L/h.

CONCLUSION

Active moiety [risperidone plus (±)-9-hydroxyrisperidone] PK variability and the covariate effects were better explained with the addition of metabolite PK parameters. This model may aid the development of individualized risperidone dosing regimens in children and adolescents.

Polymorphisms influencing olanzapine metabolism and adverse effects in healthy subjects

OBJECTIVE

The pharmacokinetics of olanzapine and response to treatment could be affected by polymorphisms in genes coding for drug-metabolizing enzymes, transporters, or receptors. The aim of this study was to identify genetic markers predictive of pharmacokinetics, pharmacodynamics, and adverse effects of olanzapine.

METHODS

Sixty-three healthy volunteers receiving a single 5-mg oral dose of olanzapine were genotyped for 39 genetic variants that could be related to the response to olanzapine. All genetic variants were analyzed by PharmaChip, but DRD2 Taq1A polymorphism was determined by real-time polymerase chain reaction. Olanzapine was measured using high-performance liquid chromatography combined with tandem mass spectrometry. The relationship of gender and polymorphisms with olanzapine pharmacokinetics, the change in prolactin levels, and the incidence of adverse effects were evaluated by multiple regression analysis.

RESULTS

The pharmacokinetics of olanzapine was influenced by polymorphisms in CYP3A5, GSTM3, and GRIN2B. Prolactin levels were affected by gender and polymorphisms in DRD2 and 5-HTR2A. Polymorphisms in CYP2C9, TPMT, UGT1A1, MDR1, and 5-HTR2A were related to some adverse effects of olanzapine.

CONCLUSIONS

Several polymorphisms can explain differences in the pharmacokinetics, pharmacodynamics, and safety of olanzapine in healthy subjects. Whether these genetic factors influence the risk of therapeutic failure or tolerability in patients remains to be established.