Clinical considerations and pitfalls in the use of depot antipsychotics.

Long-acting injectable antipsychotics (LAI) is a frequently used treatment modality which has advantages over oral antipsychotics regarding hospitalization or relapse prevention. However, the pharmacokinetic properties of LAI greatly differ from oral antipsychotics. This necessitates an increased knowledge about LAI among clinicians, especially when commencing treatment, changing doses and discontinuing treatment. In this review, we summarize an array of clinically important characteristics of LAI and give a conceptual framework for understanding the pharmacokinetics of LAI.

Evidence for Therapeutic Drug Monitoring of Atypical Antipsychotics.

Second-generation antipsychotics (SGAs), also known as atypical antipsychotics, are a newer class of antipsychotic drugs used to treat schizophrenia, bipolar disorder, and related psychiatric conditions. The plasma concentration of antipsychotic drugs is a valid measure of the drug at its primary target structure in the brain, and therefore determines the efficacy and safety of these drugs. However, despite the well-known high variability in pharmacokinetics of these substances, psychiatric medication is usually administered in uniform dosage schedules. Therapeutic drug monitoring (TDM), as the specific method that can help personalised medicine in dose adjustment according to the characteristics of the individual patient, minimizing the risk of toxicity, monitoring adherence, and increasing cost-effectiveness in the treatment, thus seems to be an elegant tool to solve this problem. Non-response to therapeutic doses, uncertain adherence to medication, suboptimal tolerability, or pharmacokinetic drug-drug interactions are typical indications for TDM of SGAs. This review aims to summarize an overview of the current knowledge and evidence of the possibilities to tailor the dosage of selected SGAs using TDM, including the necessary pharmacokinetic parameters for personalised pharmacotherapy.

Exploring clozapine pharmacokinetics in Tunisian schizophrenic patients: A population-based modelling approach investigating the impact of genetic and non-genetic variables.

Clozapine is characterized by a large within- and between-patient variability in its pharmacokinetics, attributed to non-genetic and genetic factors. A cross-sectional analysis of clozapine trough concentration (Clz C0) issued from Tunisian schizophrenic patients was collected and analysed using a nonparametric modelling approach. We assessed the impact of demographic covariates (age, weight and sex), patient's habits (smoking status, alcohol and caffeine intake) and the genetic factors (CYP1A2*1C, CYP1A2*1F and CYP2C19*2 polymorphisms) on each pharmacokinetic parameter. An external validation of this pharmacokinetic model using an independent data set was performed. Fit goodness between observed- and individual-predicted data was evaluated using the mean prediction error (% MPE), the mean absolute prediction error (% MAPE) as a measure of bias, and the root mean squared error (% RMSE) as a measure of precision. Sixty-three CLz C0 values issued from 51 schizophrenic patients were assessed in this study and divided into building and validation groups. CYP1A2*1F polymorphism and smoking status were the only covariates significantly associated with clozapine clearance. Precision parameters were as follows: 1.02%, 0.95% and 22.4%, respectively, for % MPE, % MAPE and % RMSE. We developed and validated an accurate pharmacokinetic model able to predict Clz C0 in Tunisian schizophrenic patients using the two parameters CYP1A2*1F polymorphism and smoking.

Validation of Population Pharmacokinetic Models for Clozapine Dosage Prediction.

BACKGROUND: Clozapine is unique in its capacity to ameliorate severe schizophrenia but at high risk of toxicity. A relationship between blood concentration and clinical response and evidence for concentration-response relationships to some adverse effects justify therapeutic drug monitoring of clozapine. However, the relationship between drug dose and blood concentration is quite variable. This variability is, in part, due to inductive and inhibitory interactions varying the activity of cytochrome P450 1A2 (CYP1A2), the principal pathway for clozapine elimination. Several population pharmacokinetic models have been presented to facilitate dose selection and to identify poor adherence in individual patients. These models have faced little testing for validity in independent populations or even for persisting validity in the source population. METHODS: Therefore, we collected a large population of clozapine-treated patients (127 patients, 1048 timed plasma concentrations) in whom dosing and covariate information could be obtained with high certainty. A population pharmacokinetic model was constructed with data collected in the first 6 weeks from study enrolment (448 plasma concentrations), to estimate covariate influences and to allow alignment with previously published models. The model was tested for its performance in predicting the concentrations observed at later time intervals up to 5 years. The predictive performances of 6 published clozapine population models were then assessed in the entire population. RESULTS: The population pharmacokinetic model based on the first 6 weeks identified significant influences of sex, smoking, and cotreatment with fluvoxamine on clozapine clearance. The model built from the first 6 weeks had acceptable predictive performance in the same patient population up to the first 26 weeks using individual parameters, with a median predictive error (PE) of -0.1% to -15.9% and median absolute PE of 22.9%-27.1%. Predictive performance fell progressively with time after 26 weeks. Bayesian addition of plasma concentration observations within each prediction period improved individual predictions. Three additional observations extended acceptable predictive performance into the second 6 months of therapy. When the published models were tested with the entire data set, median PE ranged from -8% to +35% with a median absolute PE of >39% in all models. Thus, none of the tested models was successful in external validation. Bayesian addition of single patient observations improved individual predictions from all models but still without achieving acceptable performances. CONCLUSIONS: We conclude that the relationship between covariates and blood clozapine concentrations differs between populations and that relationships are not stable over time within a population. Current population models for clozapine are not capturing influential covariates.

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

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

The polymorphisms of candidate pharmacokinetic and pharmacodynamic genes and their pharmacogenetic impacts on the effectiveness of risperidone maintenance therapy among Saudi children with autism.

BACKGROUND: Antipsychotics, including risperidone (RIS), are frequently indicated for various autism spectrum disorder (ASD) manifestations; however, "actionable" PGx testing in psychiatry regarding antipsychotic dosing and selection has limited applications in routine clinical practice because of the lack of standard guidelines, mostly due to the inconsistency and scarcity of genetic variant data. The current study is aimed at examining the association of RIS effectiveness, according to ABC-CV and CGI indexes, with relevant pharmacokinetics (PK) and pharmacodynamics (PD) genes. METHODS: Eighty-nine ASD children who received a consistent RIS-based regimen for at least 8 weeks were included. The Axiom PharmacoFocus Array technique was employed to generate accurate star allele-predicted phenotypes of 3 PK genes (CYP3A4, CYP3A5, and CYP2D6). Genotype calls for 5 candidate PD receptor genes (DRD1, DRD2, DRD3, HTR2C, and HTR2A) were obtained and reported as wild type, heterozygous, or homozygous for 11 variants. RESULTS: Based on the ABC total score, 42 (47.2%) children were classified as responders, while 47 (52.8%) were classified as nonresponders. Multivariate logistic regression analyses, adjusted for nongenetic factors, suggested nonsignificant impacts of the star allele-predicted phenotypes of all 3 PK genes on improvement in ASD symptoms or CGI scores. However, significant positive or negative associations of certain PD variants involved in dopaminergic and serotonergic pathways were observed with specific ASD core and noncore symptom subdomains. Our significant polymorphism findings, mainly those in DRD2 (rs1800497, rs1799978, and rs2734841), HTR2C (rs3813929), and HTR2A (rs6311), were largely consistent with earlier findings (predictors of RIS effectiveness in adult schizophrenia patients), confirming their validity for identifying ASD children with a greater likelihood of core symptom improvement compared to noncarriers/wild types. Other novel findings of this study, such as significant improvements in DRD3 rs167771 carriers, particularly in ABC total and lethargy/social withdrawal scores, and DRD1 rs1875964 homozygotes and DRD2 rs1079598 wild types in stereotypic behavior, warrant further verification in biochemical and clinical studies to confirm their feasibility for inclusion in a PGx panel. CONCLUSION: In conclusion, we provide evidence of potential genetic markers involved in clinical response variability to RIS therapy in ASD children. However, replication in prospective samples with greater ethnic diversity and sample sizes is necessary.

Virtual twins for model-informed precision dosing of clozapine in patients with treatment-resistant schizophrenia.

Model-informed precision dosing using virtual twins (MIPD-VTs) is an emerging strategy to predict target drug concentrations in clinical practice. Using a high virtualization MIPD-VT approach (Simcyp version 21), we predicted the steady-state clozapine concentration and clozapine dosage range to achieve a target concentration of 350 to 600 ng/mL in hospitalized patients with treatment-resistant schizophrenia (N = 11). We confirmed that high virtualization MIPD-VT can reasonably predict clozapine concentrations in individual patients with a coefficient of determination (R2 ) ranging between 0.29 and 0.60. Importantly, our approach predicted the final dosage range to achieve the desired target clozapine concentrations in 73% of patients. In two thirds of patients treated with fluvoxamine augmentation, steady-state clozapine concentrations were overpredicted two to four-fold. This work supports the application of a high virtualization MIPD-VT approach to inform the titration of clozapine doses in clinical practice. However, refinement is required to improve the prediction of pharmacokinetic drug-drug interactions, particularly with fluvoxamine augmentation.

Dutch Pharmacogenetics Working Group (DPWG) guideline for the gene-drug interaction between CYP2D6, CYP3A4 and CYP1A2 and antipsychotics.

The Dutch Pharmacogenetics Working Group (DPWG) aims to facilitate pharmacogenetics implementation in clinical practice by developing evidence-based guidelines to optimize pharmacotherapy. A guideline describing the gene-drug interaction between the genes CYP2D6, CYP3A4 and CYP1A2 and antipsychotics is presented here. The DPWG identified gene-drug interactions that require therapy adjustments when respective genotype is known for CYP2D6 with aripiprazole, brexpiprazole, haloperidol, pimozide, risperidone and zuclopenthixol, and for CYP3A4 with quetiapine. Evidence-based dose recommendations were obtained based on a systematic review of published literature. Reduction of the normal dose is recommended for aripiprazole, brexpiprazole, haloperidol, pimozide, risperidone and zuclopenthixol for CYP2D6-predicted PMs, and for pimozide and zuclopenthixol also for CYP2D6 IMs. For CYP2D6 UMs, a dose increase or an alternative drug is recommended for haloperidol and an alternative drug or titration of the dose for risperidone. In addition, in case of no or limited clinical effect, a dose increase is recommended for zuclopenthixol for CYP2D6 UMs. Even though evidence is limited, the DPWG recommends choosing an alternative drug to treat symptoms of depression or a dose reduction for other indications for quetiapine and CYP3A4 PMs. No therapy adjustments are recommended for the other CYP2D6 and CYP3A4 predicted phenotypes. In addition, no action is required for the gene-drug combinations CYP2D6 and clozapine, flupentixol, olanzapine or quetiapine and also not for CYP1A2 and clozapine or olanzapine. For identified gene-drug interactions requiring therapy adjustments, genotyping of CYP2D6 or CYP3A4 prior to treatment should not be considered for all patients, but on an individual patient basis only.

A Systematic Review of Clozapine Concentration-Dose Ratio from Therapeutic Drug Monitoring Studies in Children and Adolescents Treated with Clozapine for Mental Disorders.

BACKGROUND: Therapeutic drug monitoring of clozapine in children and adolescents has received insufficient attention. Calculation of concentration-to-dose (C/D) ratios from trough steady-state concentrations estimate drug clearance. METHODS: A systematic electronic literature search was conducted in 3 article databases from inception until January 10, 2023, and articles reporting clozapine concentrations in children and adolescents were retrieved. The pharmacokinetic quality of the studies was assessed, and clozapine C/D ratios were calculated using the sample mean clozapine dose and concentration. RESULTS: Of the 37 articles of potential interest, only 7 reported clozapine trough and steady-state concentrations. After excluding case reports and a study confounded by fluvoxamine, 4 studies on psychosis from Europe and the United States were included. The clozapine C/D ratios were similar to published adult values and ranged from 0.82 to 1.24 with a weighted mean of 1.08 ng/mL per mg/d. The weighted means were 334 mg/d for the dose and 380 ng/mL for the concentration. The stratified analysis of the weighted mean clozapine C/D ratios from 2 studies showed lower values in 52 male (1.05 ng/mL per mg/d) than in 46 female (1.46 ng/mL per mg/d) children and adolescents, with values similar to those reported for European adult nonsmokers. Two female adolescents had high clozapine C/D ratios (2.54 ng/mL per mg/d), an Asian American patient with borderline obesity and a patient with intellectual disability with low dosage (mean = 102 mg/d) and concentration (mean = 55 ng/mL). CONCLUSIONS: Reports on clozapine therapeutic drug monitoring in children and adolescents are limited in number and quality. Future studies should focus on basic pharmacokinetic issues, such as stratification by sex, smoking, and relevant comedications with inductive or inhibitory properties.

Relationship of the 1846G > A Polymorphism of the CYP2D6 Gene to the Equilibrium Concentration Levels of Haloperidol in Patients with Acute Alcoholic Hallucinosis.

Haloperidol is currently used in addictology for the treatment of acute psychotic disorders, including acute alcoholic hallucinosis. The use of haloperidol is often accompanied by the occurrence of adverse drug reactions (ADRs). There is evidence that CYP2D6 isoenzyme is involved in the biotransformation of haloperidol. Aim: The study aimed to evaluate the relationship of 1846G > A polymorphism of the CYP2D6 gene to the equilibrium concentration levels of haloperidol in patients with acute alcoholic hallucinosis. Material and Methods: The study was conducted on 100 male patients with acute alcoholic hallucinosis (mean age 41.4 ± 14.4 years). The efficacy profile was evaluated using the PANSS (Positive and Negative Syndrome Scale) scale. The safety of therapy was assessed using the UKU Side-Effect Rating Scale and the SAS (Simpson-Angus Scale for Extrapyramidal Symptoms) scale. Genotyping was performed using the real-time polymerase chain reaction (Real-time PCR). Equilibrium plasma concentration levels of haloperidol were investigated using the high-performance liquid chromatography with mass spectrometry (HPLC with MS/MS). Results: No statistically significant results were obtained during the therapy efficacy assessment (dynamics of the PANSS score: GG genotype (-13.00 [-16.00; -16.00; -11.00]), GA genotype (-15.00 [-16.75; -13.00], p = 0.728). There was a statistically significant difference in safety assessment scores (dynamics of the UKU score: GG genotype (8.00 [7.00; 10.00]), GA genotype (15.00 [9.25; 18.00], p < 0.001); dynamics of the SAS score: GG genotype (11.00 [9.00; 14.00]), GA genotype (14.50 [12.00; 18.00], p < 0.001). The pharmacokinetic study results showed a statistically significant difference: GG (3.13 [2.32; 3.95]), GA (3.89 [2.92; 5.26], p = 0.010). Thus, a study conducted on a group of 100 patients with acute alcoholic hallucinosis demonstrated an association between the 1846G > A polymorphism of the CYP2D6 gene (rs3892097) and the safety profile of haloperidol therapy. We also revealed the presence of statistically significant difference in the equilibrium concentration levels of haloperidol in patients with the GG and AG genotypes. Conclusion: It can be concluded that patients with the GA genotype have a higher risk of ADRs compared to patients carrying the GG genotype. It is shown that 1846G > A polymorphism of the CYP2D6 gene (rs3892097) has a statistically significant effect on the equilibrium concentration levels of haloperidol.

Drug-drug interactions between antiseizure medications and antipsychotic medications: a narrative review and expert opinion.

INTRODUCTION: Antiseizure medications (ASMs) and antipsychotic drugs are frequently coadministered with the potential for drug-drug interactions. Interactions may either be pharmacokinetic or pharmacodynamic, resulting in a decrease or increase in efficacy and/or an increase or decrease in adverse effects. AREAS COVERED: The clinical evidence for pharmacokinetic and pharmacodynamic interactions between ASMs and antipsychotics is reviewed based on the results of a literature search in MEDLINE conducted in April 2023. EXPERT OPINION: There is now extensive published evidence for the clinical importance of interactions between ASMs and antipsychotics. Enzyme-inducing ASMs can decrease blood concentrations of many of the antipsychotics. There is also evidence that enzyme-inhibiting ASMs can increase antipsychotic blood concentrations. Similarly, there is limited evidence showing that antipsychotic drugs may affect the blood concentrations of ASMs through pharmacokinetic interactions. There is less available evidence for pharmacodynamic interactions, but these can also be important, as can displacement from protein binding. The lack of published evidence for an interaction should not be interpreted as meaning that the given interaction does not occur; the evidence is building continually. There is no substitute for careful patient monitoring and sound clinical judgment.

Role of Modeling and Simulation in Preclinical and Clinical Long-Acting Injectable Drug Development.

Innovations in the field of long-acting injectable drug development are increasingly being reported. More advanced in vitro and in vivo characterization can improve our understanding of the injection space and aid in describing the long-acting injectable (LAI) drug's behavior at the injection site more mechanistically. These innovations may enable unlocking the potential of employing a model-based framework in the LAI preclinical and clinical space. This review provides a brief overview of the LAI development process before delving deeper into the current status of modeling and simulation approaches in characterizing the preclinical and clinical LAI pharmacokinetics, focused on aqueous crystalline suspensions. A closer look is provided on in vitro release methods, available biopharmaceutical models and reported in vitro/in vivo correlations (IVIVCs) that may advance LAI drug development. The overview allows identifying the opportunities for use of model-informed drug development approaches and potential gaps where further research may be most warranted. Continued investment in improving our understanding of LAI PK across species through translational approaches may facilitate the future development of LAI drug products.

Clinical pharmacokinetics of antipsychotics in pediatric populations: a scoping review focusing on dosing regimen.

INTRODUCTION: Achieving optimal clinical responses and minimizing side effects through precision dosing of antipsychotics in children and adolescents with psychiatric disorders remains a challenge. Identifying patient characteristics (covariates) that affect pharmacokinetics can inform more effective dosing strategies and ultimately improve patient outcomes. This review aims to provide greater insight into the impact of covariates on the clinical pharmacokinetics of antipsychotics in pediatric populations. AREAS COVERED: A comprehensive literature search was conducted, and the main findings regarding the effects of the covariates on the pharmacokinetics of antipsychotics in children and adolescents are presented. EXPERT OPINION: Our study highlights significant covariates, including age, sex, weight, CYP2D6 phenotype, co-medication, and smoking habits, which affect the pharmacokinetics of antipsychotics. However, the findings were generally limited by the small sample sizes of naturalistic, open-label, observational studies, and the homogeneous subgroups. Dosing based on weight and preemptive genotyping could prove beneficial for optimizing the dosing regimen in pediatric populations. Future research is needed to refine dosing recommendations and establish therapeutic reference ranges critical for precision dosing and Therapeutic Drug Monitoring (TDM). The integration of individual patient characteristics with TDM can further optimize the efficacy and safety of antipsychotics for each patient.

Population Pharmacokinetic Analysis of Brexpiprazole to Support its Indication and Dose Selection in Adolescents With Schizophrenia.

Due to the customary delay between medication approvals in adult and adolescent populations, adolescents with schizophrenia may receive off-label antipsychotic treatment, without empirically justified dosing recommendations. In order to accelerate pediatric drug development, the US Food and Drug Administration (FDA) released a general advice letter to sponsors permitting the effectiveness of atypical antipsychotics for the treatment of schizophrenia in adults to be extrapolated to adolescents based on a pharmacokinetic (PK) analysis to support dose selection, plus a safety study. The aim of the present article is to describe the population PK analysis that was submitted to the FDA to inform brexpiprazole dose selection in adolescents with schizophrenia. Using a population PK model with brexpiprazole clearance and volume of distribution allometrically scaled by body weight, PK simulations showed comparable brexpiprazole dose-exposure between adults and adolescents aged 13-17 years following oral daily doses of brexpiprazole 1-4 mg, indicating that the target brexpiprazole dose of 2-4 mg/day in adults with schizophrenia is also suitable for adolescents. Based on this population PK analysis, together with a safety study in adolescents, the FDA approved brexpiprazole for the treatment of schizophrenia in adolescents aged 13-17 years, via extrapolation of the efficacy of brexpiprazole from adults to adolescents.

Pharmacokinetics and pharmacogenomics of clozapine in an ancestrally diverse sample: a longitudinal analysis and genome-wide association study using UK clinical monitoring data.

BACKGROUND: The antipsychotic, clozapine, is the only licensed drug against the treatment-resistant symptoms that affect 20-30% of people with schizophrenia. Clozapine is markedly underprescribed, partly because of concerns about its narrow therapeutic range and adverse drug reaction profile. Both concerns are linked to drug metabolism, which varies across populations globally and is partly genetically determined. Our study aimed to use a cross-ancestry genome-wide association study (GWAS) design to investigate variations in clozapine metabolism within and between genetically inferred ancestral backgrounds, to discover genomic associations to clozapine plasma concentrations, and to assess the effects of pharmacogenomic predictors across different ancestries. METHODS: In this GWAS, we analysed data from the UK Zaponex Treatment Access System clozapine monitoring service as part of the CLOZUK study. We included all available individuals with clozapine pharmacokinetic assays requested by their clinicians. We excluded people younger than 18 years, or whose records contained clerical errors, or with blood drawn 6-24 h after dose, a clozapine or norclozapine concentration less than 50 ng/mL, a clozapine concentration of more than 2000 ng/mL, a clozapine-to-norclozapine ratio outside of the 0·5-3·0 interval, or a clozapine dose of more than 900 mg/day. Using genomic information, we identified five biogeographical ancestries: European, sub-Saharan African, north African, southwest Asian, and east Asian. We did pharmacokinetic modelling, a GWAS, and a polygenic risk score association analysis using longitudinal regression analysis with three primary outcome variables: two metabolite plasma concentrations (clozapine and norclozapine) and the clozapine-to-norclozapine ratio. FINDINGS: 19 096 pharmacokinetic assays were available for 4760 individuals in the CLOZUK study. After data quality control, 4495 individuals (3268 [72·7%] male and 1227 [27·3%] female; mean age 42·19 years [range 18-85]) linked to 16 068 assays were included in this study. We found a faster average clozapine metabolism in people of sub-Saharan African ancestry than in those of European ancestry. By contrast, individuals with east Asian or southwest Asian ancestry were more likely to be slow clozapine metabolisers than those with European ancestry. Eight pharmacogenomic loci were identified in the GWAS, seven with significant effects in non-European groups. Polygenic scores generated from these loci were associated with clozapine outcome variables in the whole sample and within individual ancestries; the maximum variance explained was 7·26% for the metabolic ratio. INTERPRETATION: Longitudinal cross-ancestry GWAS can discover pharmacogenomic markers of clozapine metabolism that, individually or as polygenic scores, have consistent effects across ancestries. Our findings suggest that ancestral differences in clozapine metabolism could be considered for optimising clozapine prescription protocols for diverse populations. FUNDING: UK Academy of Medical Sciences, UK Medical Research Council, and European Commission.

Relationship Between Plasma Aripiprazole and Dehydroaripiprazole Concentrations and Prolactin Levels in Chinese Children and Adolescents.

Objective: To investigate the relationship between plasma aripiprazole (ARI) and its metabolite dehydroaripiprazole (DARI) concentrations and prolactin (PRL) levels in Chinese children and adolescents. Methods: This was a retrospective cross-sectional study and the data were collected at Beijing HuiLongGuan Hospital, a Beijing City owned psychiatric hospital, between January 1 and December 31, 2021. Fifty-two child and adolescent inpatients (17 males, 35 females) aged 13-18 years and received ARI regardless of diagnosis were included. The steady-state ARI and DARI plasma concentrations were measured using high-performance liquid chromatography-tandem mass spectrometry. The serum PRL levels were measured by chemiluminescence immunoassay. Results: The plasma concentrations of ARI, DARI, and the total of ARI and DARI were negatively correlated with serum PRL levels in female children and adolescents. Approximately 15% of child and adolescent inpatients treated with ARI exhibited subnormal PRL serum levels. Conclusions: The results suggest that in addition to regularly monitoring PRL levels, therapeutic drug monitoring for ARI and its main metabolite DARI can help to mitigate the adverse medical consequences associated with PRL reduction. Thus, clinicians should consider the ARI-induced reduction of PRL levels when prescribing ARI to child and adolescent patients, particularly among females.

Modeling Approach with Therapeutic Drug Monitoring Data to Describe Time Course of Clozapine Exposure and Positive and Negative Syndrome Scale Scores.

OBJECTIVE: The Positive and Negative Syndrome Scale (PANSS) is commonly used to assess the severity of the clinical symptoms of schizophrenia (SCZ). This study aimed to develop a pharmacokinetic (PK)/pharmacodynamic (PD) model based on therapeutic drug monitoring (TDM) data to characterize the relationship between clozapine exposure and the PANSS scores in patients with SCZ. METHODS: TDM data for clozapine and PANSS scores from 45 patients with SCZ were included in this modeling analysis using NONMEM. Based on published data, intensive PK sampling data collected up to 12 hours postdose from 23 patients was incorporated into the PK data set to improve the fitting of absorption and disposition. For PD model development, the PANSS score was assessed at baseline, followed by 8 and 18 weeks after the initiation of clozapine dosing. Visual predictive check plots, the precision of parameter estimates, and decreases in the minimum objective function values were used for the model evaluation. RESULTS: A 2-compartment model with an absorption lag and a combined error model adequately described the PK of clozapine. The implementation of disease progression with placebo and drug effects improved the model's ability to describe the time course of the PANSS scores. In the final PK/PD model, Weibull and maximum effect (E max ) models were selected as disease progression models for the placebo and drug effect models, respectively. The model evaluation results supported the adequacy of the final model. CONCLUSIONS: A clozapine PK/PD model based on clinical settings adequately described the PANSS time course in patients with SCZ. These findings may aid the development of treatment strategies for patients with SCZ.

Drug-drug interactions involving combinations of antipsychotic agents with antidiabetic, lipid-lowering, and weight loss drugs.

INTRODUCTION: Patients with severe mental illness (SMI) have a high risk for diabetes, dyslipidemia, and other components of metabolic syndrome. Patients with these metabolic comorbidities and cardiac risk factors should receive not only antipsychotics but also medications aiming to reduce cardiovascular risk. Therefore, many patients may be exposed to clinically relevant drug-drug interactions. AREAS COVERED: This narrative review summarizes data regarding the known or potential drug-drug interactions between antipsychotics and medications treating metabolic syndrome components, except for hypertension, which has been summarized elsewhere. A literature search in PubMed and Scopus up to 7/31/2021 was performed regarding interactions between antipsychotics and drugs used to treat metabolic syndrome components, aiming to inform clinicians' choice of medication for patients with SMI and cardiometabolic risk factors in need of pharmacologic interventions. EXPERT OPINION: The cytochrome P450 system and, to a lesser extent, the P-glycoprotein transporter is involved in the pharmacokinetic interactions between antipsychotics and some statins or saxagliptin. Regarding pharmacodynamic interactions, the available information is based mostly on small studies, and for newer classes, like PCSK9 inhibitors or SGLT2 inhibitors, data are still lacking. However, there is sufficient information to guide clinicians in the process of selecting safer antipsychotic-cardiometabolic risk reduction drug combinations.

Amisulpride steady-state plasma concentration and adverse reactions in patients with schizophrenia: a study based on therapeutic drug monitoring data.

The aim of the study was to evaluate the reference range of amisulpride for Chinese patients with schizophrenia and to assess its possible influencing factors based on therapeutic drug monitoring information. The relative adverse reactions of patients induced by amisulpride were also systematically investigated. A total of 425 patients with schizophrenia were assessed, including Positive and Negative Syndrome Scales, Treatment Emergent Symptom Scale, blood routine examination, hepatorenal function, lipids, hormones, as well as myocardial enzymes at baseline, and following treatment with amisulpride for 8 weeks. The steady-state plasma concentration of amisulpride was assayed using two-dimensional liquid chromatography. At the same dose, the amisulpride plasma concentration of patients combined with clozapine was higher than that without clozapine. The therapeutic reference range of amisulpride can be defined as 230.3-527.1 ng/ml for Chinese patients with schizophrenia. The potential side effects appear to be associated with significantly increased levels of LDH, CK, creatine kinase isoenzyme (CK-MB), TC and decreased level of E 2 , relative to the amisulpride plasma concentration. These findings could provide individualized medication and reduce the adverse effects of amisulpride for Chinese patients with schizophrenia.

Drug-drug interactions involving antipsychotics and antihypertensives.

INTRODUCTION: Antipsychotics represent the mainstay in the treatment of patients diagnosed with major psychiatric disorders. Hypertension, among other components of metabolic syndrome, is a common finding in these patients. For their psychiatric and physical morbidity, many patients receive polypharmacy, exposing them to the risk of clinically relevant drug-drug interactions. AREAS COVERED: This review summarizes the knowledge regarding the known or potential drug-drug interactions between antipsychotics and the main drug classes used in the treatment of hypertension. We aimed to provide the clinician an insight into the pharmacokinetic and pharmacodynamic interactions between these drugs for a better choice of combinations of drugs to treat both the mental illness and cardiovascular risk factors. For this, we performed a literature search in PubMed and Scopus databases, up to 31 July 2021. EXPERT OPINION: The main pharmacokinetic interactions between antipsychotics and antihypertensive drugs involve mainly the cytochrome P450 system. The pharmacodynamic interactions are produced by multiple mechanisms, leading to concurrent binding to the same receptors. The data available regarding drug-drug interactions is mostly based on case reports and small studies and therefore should be interpreted with caution. The current knowledge is sufficiently strong to guide clinicians in selecting safer drug combinations as summarized here.