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.

A population pharmacokinetic model to guide clozapine dose selection, based on age, sex, ethnicity, body weight and smoking status.

AIMS: Guidance on clozapine dosing in treatment-resistant schizophrenia is based largely on data from White young adult males. This study aimed to investigate the pharmacokinetic profiles of clozapine and N-desmethylclozapine (norclozapine) across the age range, accounting for sex, ethnicity, smoking status and body weight. METHODS: A population pharmacokinetic model, implemented in Monolix, that linked plasma clozapine and norclozapine via a metabolic rate constant, was used to analyse data from a clozapine therapeutic drug monitoring service, 1993-2017. RESULTS: There were 17 787 measurements from 5960 patients (4315 male) aged 18-86 years. The estimated clozapine plasma clearance was reduced from 20.2 to 12.0 L h-1 between 20 and 80 years. Model-based dose predictions to attain a predose plasma clozapine concentration of 0.35 mg L-1 was 275 (90% prediction interval 125, 625) mg day-1 in nonsmoking, White males weighing 70 kg and aged 40 years. The corresponding predicted dose was increased by 30% in smokers, decreased by 18% in females, and was 10% higher and 14% lower in otherwise analogous Afro-Caribbean and Asian patients, respectively. Overall, the predicted dose decreased by 56% between 20 and 80 years. CONCLUSION: The large sample size and wide age range of the patients studied allowed precise estimation of dose requirements to attain predose clozapine concentration of 0.35 mg L-1 . The analysis was, however, limited by the absence of data on clinical outcome and future studies are required to determine optimal predose concentrations specifically in those aged over 65 years.

Lorazepam in catatonia - Past, present and future of a clinical success story.

The effect of lorazepam in the treatment of catatonia is outstanding and almost immediate. Clinicians are familiar with its effects: mute patients can speak again, akinetic patients can move again and patients with negativism can eat and drink again within usually a short duration of about 10 min to 1-2 h. Fear is often gone after lorazepam administration. While not always effective, the introduction of lorazepam into clinical practice represented a breakthrough and was often life-saving for many patients suffering from catatonia. It is rare to observe such rapid therapeutic effects in other domains of psychiatry. In this narrative review we will briefly look at the past, present and future of lorazepam in the treatment of catatonia. It is gratifying to reflect on the fact that clinicians using the age-old medical practice of observation and empirical treatment succeeded in advancing the management of catatonia 40 years ago. The present evidence shows that the clinical effect of lorazepam in catatonia treatment is excellent and more or less immediate although it remains to be explicitly tested against other substances such as diazepam, zolpidem, clozapine, quetiapine, amantadine, memantine, valproate and dantrolene in randomized clinical trials. In addition, future studies need to answer the question how long lorazepam should be given to patients with catatonia, months or even years? This narrative review promotes the rapid use of lorazepam in the treatment of acute catatonic patients and stipulates further scientific examination of its often impressive clinical effects.

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.

Schizophrenia patients discharged on antipsychotic polypharmacy from a public psychiatric hospital in Taiwan, 2006-2021.

The aim of this study was to identify the factors associated with antipsychotic polypharmacy (APP), investigate whether APP could affect the risk of rehospitalization, and explore temporal trends in APP use. Schizophrenia patients discharged from the study hospital between 2006 and 2021 (n = 16,722) were included in the analysis. The logistic regression model was employed to determine the predictors significantly associated with APP use. Survival analysis was used to compare time to rehospitalization between APP and antipsychotic monotherapy (AMT). The temporal trend of APP use was analyzed using the Cochran-Armitage Trend test. In comparison with the patients (n = 10,909) who were discharged on AMT, those (n = 5,813) on APP were significantly more likely to be male gender, to receive LAIs, to take clozapine, to take anticholinergic agents, to have a greater number of previous hospitalizations, and to have a higher CPZ equivalent dose of antipsychotic prescription. The prescription rate of APP significantly increased from 18.4 % in 2006 to 44.9 % in 2021. Compared with AMT, APP was associated with more clozapine use, more LAI use, higher doses of antipsychotics, and an increased risk of rehospitalization. In addition, the prescription of APP continued to increase during the study period.

Effect of Cigarette Smoking on Clozapine Dose and on Plasma Clozapine and N-Desmethylclozapine (Norclozapine) Concentrations in Clinical Practice.

BACKGROUND: Cigarette smoking enhances plasma clozapine clearance and thus affects the clozapine dose requirement. METHODS: We compared clozapine daily dose and plasma clozapine and N-desmethylclozapine (norclozapine) concentrations in male and female smokers and nonsmokers in samples submitted for clozapine therapeutic drug monitoring (1996-2017). RESULTS: There were 105,316/60,792 and 34,290/31,309 samples with dose information from male and female smokers/nonsmokers, respectively. There was information on the number of cigarettes smoked daily for 12,842 samples (8409 patients) and 3948 samples (2753 patients) from men and women, respectively. Of these, 574 and 253 samples were from men and women, respectively, who reported smoking 1-9 cigarettes daily.In both sexes, the median clozapine doses in the nonsmokers were 75%-80% of those in the smokers, but the median plasma clozapine and norclozapine concentrations were 136% higher. The effect of smoking on the dose and on median plasma clozapine and norclozapine concentrations seemed maximal after 2-3, perhaps fewer, cigarettes daily in males. In females, the effect of smoking seemed to be near maximal after some 4-5 cigarettes per day. IMPLICATIONS: The optimum target range for predose plasma clozapine may be different in smokers (0.35-0.45 mg L-1) as opposed to nonsmokers (0.50-0.60 mg L-1). That changes in clozapine clearance are likely near maximal with cigarette smoking as low as 2-3 d-1 in males, perhaps slightly more in females, emphasizes that covert or passive smoking may be an important factor in seemingly random changes in plasma clozapine concentration at constant dose.

Characterization of antipsychotic utilization before clozapine initiation for individuals with schizophrenia: an innovative visualization of trajectories using French National Health Insurance data.

AIMS: Despite recommendations to initiate clozapine after two unsuccessful trials of antipsychotics, clozapine is underprescribed and initiated too late. The aim of this study was to describe different antipsychotic treatment sequences in the 36 months before the initiation of clozapine and to characterize clusters of treatment trajectories. METHODS: Using the French National Health Insurance database, a historical cohort study of the population in an area in western France was performed. The data from all new users of clozapine with a diagnosis of schizophrenia or schizoaffective disorder in the period of 2017-2018 were evaluated. All outpatient reimbursements for antipsychotics during the 36 months before clozapine initiation were analysed. Successive reimbursements for identical treatments were grouped into treatment trials (TTs), and different trajectories were clustered using a state sequence analysis. RESULTS: The results showed 1191 TTs for 287 individuals. The mean number of TTs per individual was 3.2. Risperidone, aripiprazole and haloperidol were the main treatments delivered. The frequencies of antipsychotics used differed between monotherapies and combination therapies. A three-cluster typology was identified: one cluster (n = 133) of 'less treated' younger individuals with fewer TTs and shorter TT durations; a second cluster (n = 53) of 'more treated' individuals with higher numbers of TTs and combinations of antipsychotics; and a third cluster (n = 103) of 'treatment-stable' older individuals with longer TT durations. CONCLUSIONS: The results indicate that the median number of TTs during the 36 months before clozapine prescription was higher than the two recommended. The different trajectories were associated with individual characteristics and treatment differences, suggesting that additional studies of clinical parameters are needed to understand barriers to clozapine prescription.

Association of clozapine and norclozapine levels with patient and therapy characteristics-focus on interaction with valproic acid.

PURPOSE: The goal of the study was to examine clozapine (CLZ) and norclozapine (NCLZ) therapeutic drug monitoring (TDM) data and associated sources of pharmacokinetic variability, particularly the impact of valproic acid (VPA) use. METHODS: This study included 126 patients with psychiatric disorders on mono- or co-therapy with CLZ. Patients' data during routine TDM were collected retrospectively from clinical records. The descriptive and statistical analysis was computed using IBM SPSS Statistics software (version 22, NY, USA). Multiple linear regression, based on the last observations, was used to assess correlation between demographic characteristics, life habits and co-therapy with dose-corrected serum levels (C/D) of CLZ and NCLZ, as well as CLZ/NCLZ. RESULTS: A total of 295 CLZ concentrations were measured in 126 patients, with a mean of 275.5 ± 174.4 µg/L, while 124 NCLZ concentrations were determined in 74 patients, with a mean of 194.6 ± 149.8 µg/L. A statistically significant effect on ln-transformed CLZ C/D was confirmed for sex and smoking, whereas sex, smoking and VPA therapy were associated with ln-transformed NCLZ C/D. According to the final models, lower values of NCLZ C/D for about 45.9% can be expected in patients receiving VPA. Concomitant use of VPA was the only factor detected to contribute in CLZ/NCLZ variability. CONCLUSION: The results of this study may help clinicians interpret TDM data and optimize CLZ dosing regimens, especially in patients concomitantly treated with VPA. Our results show that VPA primarily decreases NCLZ levels, while alteration of the parent drug is not statistically significant.

Effect of smoking habits and concomitant valproic acid use on relapse in patients with treatment-resistant schizophrenia receiving clozapine: A 1-year retrospective cohort study.

INTRODUCTION: No study has investigated the impact of smoking habits and concomitant valproic acid (VPA) use on clinical outcomes in maintenance treatment with clozapine. Thus, we aimed to examine the effect of smoking habits and concomitant VPA use on relapse during the first year after discharge in patients with treatment-resistant schizophrenia (TRS) receiving clozapine. METHODS: This retrospective cohort study included patients with TRS who were initiated on clozapine during hospitalization and discharged between April 2012 and January 2021 in two tertiary psychiatric hospitals in Japan. Relapse was defined as rehospitalization due to psychiatric exacerbation during the first year after discharge. A multivariable Cox proportional hazards regression analysis was performed to analyze the effect of smoking habits and concomitant VPA use on relapse. Subgroup analyses were also conducted to examine potential interactions between smoking habits and concomitant VPA use. RESULTS: Among the included 192 patients, 69 (35.9%) met the criteria of relapse. While smoking habits (adjusted hazard ratio [aHR], 2.27; 95% confidence interval [CI], 1.28-4.01; p < 0.01) independently increased the risk of relapse, a significant interaction for relapse risk was found between smoking habits and concomitant VPA use (p-interaction = 0.015). Concomitant VPA use may be an effective modifier of the increased relapse risk associated with smoking habits. Among patients who smoked, those using VPA concomitantly exhibited a higher risk of relapse (aHR, 5.32; 95% CI, 1.68-16.9; p < 0.01) than those not using VPA (aHR, 1.41; 95% CI, 0.73-2.70; p = 0.30). CONCLUSION: The findings suggest that the combination of smoking habits and concomitant VPA use may increase the risk of relapse after discharge. Future studies are required to elucidate the mechanisms underlying these findings, such as a decrease in clozapine blood levels.

Nationwide study on antipsychotic polypharmacy among forensic psychiatric patients.

This nationwide retrospective cross-sectional study examines the prevalence of antipsychotic polypharmacy (APP) and demographic, forensic, and clinical factors associated with its practice among Greenlandic forensic psychiatric patients. We collected data from electronic patient files, court documents, and forensic psychiatric assessments. We defined APP as two or more concurrent prescriptions of antipsychotic medication. The study population of 74 patients had a mean age of 41.4 years, and 61 were men. All included patients had either schizophrenia or another ICD-10 F2-diagnosis. We used unpaired t-tests and Chi2 or Fisher's exact test. The prevalence of APP was 35% (n = 26), and there was a significant association between APP and a prescription of clozapine (Chi2, p = 0.010), olanzapine (Fisher's test, p = 0.003), and aripiprazole (Fisher's test, p = 0.013). Furthermore, we found a significant association between APP and prescription of a first-generation antipsychotic (FGA) (Chi2, p = 0.011). Despite recommendations in guidelines, the use of APP is common practice. The majority of forensic psychiatric patients suffer from severe psychiatric disorders, often with other comorbidities, including substance use disorder. The severity and complexity in mental health render forensic psychiatric patients at high risk of APP treatment. Further knowledge on APP use is crucial to secure and further improve the psychopharmacological treatment for this group of patients.

Hematological and Other Cancers in People Using Clozapine: Analysis of Australian Spontaneous Reports Between 1995 and 2020.

BACKGROUND: Recent observational study evidence suggests that clozapine, unlike other antipsychotics, may be associated with a small increased risk of hematological malignancy. This study described characteristics of hematological and other cancers in those taking clozapine reported to the Australian Therapeutic Goods Administration. METHODS: We analyzed public case reports for "clozapine," "Clozaril," or "Clopine" from January 1995 to December 2020 classified as "neoplasm benign, malignant and unspecified" by the Australian Therapeutic Goods Administration. Data on age, sex, dose, clozapine start and cessation dates, Medical Dictionary for Regulatory Activities reaction terms, and date of cancer were extracted. RESULTS: Overall, 384 spontaneous reports of cancers in people taking clozapine were analyzed. The mean age of patients was 53.9 years (SD, 11.4 years), and 224 (58.3%) were male. The most frequent cancers were hematological (n = 104 [27.1%]), lung (n = 50 [13.0%]), breast (n = 37 [9.6%]), and colorectal (n = 28 [7.3%]). The outcome was fatal for 33.9% of cancer reports. Lymphoma comprised 72.1% of all hematological cancers (mean patient age, 52.1 years; SD, 11.6 years). The median daily dose of clozapine at the time of hematological cancer report was 400 mg (interquartile range, 300-543.8 mg), and the median duration of clozapine use before hematological cancer diagnosis was 7.0 years (interquartile range, 2.8-13.2 years). CONCLUSIONS: Lymphoma and other hematological cancers are overrepresented in spontaneous adverse event reports compared with other cancer types. Clinicians should be aware of the possible association with hematological cancers and monitor for and report any hematological cancers identified. Future studies should examine histology of lymphomas in people using clozapine and corresponding blood level of clozapine.

Guía práctica para el uso de clozapina en niños/as y adolescentes / Practical guidelines for the use of clozapine in children and adolescents

El uso de clozapina (CZP) en niños/as y adolescentes ha estado históricamente limitado, debido a los efectos adversos y riesgos médicos asociados al fármaco, a pesar de ser una herramienta farmacológica de gran efectividad en la psiquiatría general. A continuación, se presenta una guía clínica con los siguientes objetivos: 1) identificar los criterios de indicación de CZP en niños, niñas y adolescentes (NNA) según la evidencia disponible; 2) entregar algunas directrices a los clínicos y profesionales de salud respecto a la prescripción de CZP y precauciones a tener en consideración en esta población y; 3) entregar algunos datos comparativos del uso de CZP entre población infantojuvenil y población adulta. Todo lo anterior tiene como finalidad poder entregar la información necesaria para que los clínicos no limiten el uso de este fármaco y puedan prescribirlo de acuerdo con la evidencia científica disponible.

The use of clozapine (CZP) in children and adolescents has historically been limited due to the adverse effects and medical risks commonly associated with the drug, despite being a highly effective pharmacological tool in general psychiatry. Below we developed a clinical guideline with the following objectives: 1) identify the indication criteria for CZP in children and adolescents (NNA) according to the available evidence; 2) provide some guidelines to clinicians and health professionals regarding the prescription of CZP and precautions to be taken into account in this population and; 3) provide some comparative data on the use of CZP between the pediatric and adult population. The purpose of the guideline is to provide the necessary information so that clinicians do not limit the use of CLZ when needed and can prescribe it safely and according to the available scientific evidence.

Co-medication with disulfiram markedly increased serum clozapine levels: Two case reports.

BACKGROUND: Alcohol use disorder (AUD) is a significant co-morbidity in patients with schizophrenia. Clozapine offers some benefits in treating patients with refractory schizophrenia and AUD, but co-medicating with disulfiram is also common. PROCEDURES: We report two cases where co-medicating with disulfiram led to a significant increase in clozapine serum levels. FINDINGS: Clozapine serum levels decreased to one-third in Patient 1 when disulfiram was discontinued and started to increase again when disulfiram was reintroduced. Patient 2 developed toxic serum levels of clozapine during disulfiram treatment combined with heavy coffee drinking and symptoms reminiscent of neuroleptic malignant syndrome. CONCLUSIONS: Clozapine and disulfiram are both metabolized by cytochrome P450 CYP1A2 and clinically relevant interaction through this shared pathway is possible.

Effects of clozapine treatment on the improvement of substance use disorders other than nicotine in individuals with schizophrenia spectrum disorders: A systematic review and meta-analysis.

BACKGROUND: Antipsychotic medications are the mainstay of treatment for schizophrenia and are associated with a reduction in psychiatric hospitalization and overall mortality. Some evidence suggest that antipsychotic medications might have a varying effect on the improvement of comorbid substance use disorders (SUDs), with clozapine showing more favorable outcomes. AIM: We systematically reviewed all available evidence on effects of clozapine on the improvement of SUDs other than nicotine. METHODS: Electronic searches of MEDLINE, Embase, PsycINFO, and CINHAL were conducted up to March 1, 2022. Studies of any methodological design involving two concepts: (1) clozapine and (2) SUD terms (excluding nicotine) were included. For SUD outcomes with three or more comparative studies with available raw data meta-analysis was performed. SUD outcomes not meeting criteria for meta-analysis were described qualitatively. Risk of bias was examined using "Downs and Black," and "Q-Coh" instruments. RESULTS: The majority of individuals in the included 31 studies were male and of European ancestry. Abstinence was the most common outcome. Most of the studies were of low-to-moderate quality, and none of the studies met all the quality criteria. Pooled findings from four observational studies in samples of patients with predominantly comorbid alcohol use disorder showed that clozapine treatment is associated with significantly higher odds of remaining abstinent. In addition clozapine was associated with decreased odds of psychiatric hospitalization in all but one observational study. CONCLUSIONS: Our systematic review and meta-analysis builds upon previous reviews, and it suggests the association of clozapine treatment with significantly higher odds of remaining abstinent from substance use and decreased likelihood of psychiatric hospitalization, compared with continuing treatment with other antipsychotic medications. Still, the validity of this association needs greater exploration and providing recommendations for the utility of clozapine in individuals without treatment-resistant psychosis and comorbid SUDs would be premature.

Influence of glutathione-related genetic variants on the oxidative stress profile of Mexican patients with psychotic disorders.

OBJECTIVE: The clinical trajectories of patients with psychotic disorders have divergent outcomes, which may result in part from glutathione (GSH)-related high-risk genotypes. We aimed to determine pharmacokinetics of clozapine, GSH levels, GSH peroxidase (GPx) activity, gene variants involved in the synthesis and metabolism of GSH, and their association with psychotic disorders in Mexican patients on clozapine monotherapy and controls. METHODS: The sample included 75 patients with psychotic disorders on clozapine therapy and 40 paired healthy controls. Plasma clozapine/N-desmethylclozapine, GSH concentrations, and GPx activity were determined, along with genotyping of GCLC and GSTP1 variants and copy number variations of GSTP1, GSTT1, and GSTM1. Clinical, molecular and biochemical data were analyzed with a logistic regression model. RESULTS: GSH levels were significantly reduced and, conversely, GPx activity was higher in PD patients compared to controls. GCLC_GAG-7/9 genotype (OR=4.3, CI95=1.40-14.31, p=0.019) and hetero-/homozygous genotypes of GCLC_rs761142 (OR=6.09, CI95=1.93-22.59, p=0.003) were found as risk factors for psychosis. The genetic variants were not related to clozapine/N-desmethylclozapine levels or to metabolic ratio. CONCLUSIONS: GCLC variants were associated with the oxidative stress profile of PD patients raising opportunities for intervention to improve their antioxidant defenses. Further studies with larger samples should explore this proposal.

Electroconvulsive therapy or clozapine for adolescents with treatment-resistant schizophrenia: an explorative analysis on symptom dimensions.

OBJECTIVE: This study sought to compare pre-intervention patient characteristics and post-intervention outcomes in a naturalistic sample of adolescent inpatients with treatment-resistant psychotic symptoms who received either electroconvulsive therapy (ECT) or clozapine. METHODS: Data of adolescents with schizophrenia/schizoaffective disorder receiving ECT or clozapine were retrospectively collected from two tertiary-care psychiatry-teaching university hospitals. Subscale scores of the Positive and Negative Symptom Scale (PANSS) factors were calculated according to the five-factor solution. Baseline demographics, illness characteristics, and post-intervention outcomes were compared. RESULTS: There was no significant difference between patients receiving ECT (n = 13) and clozapine (n = 66) in terms of age, sex, and the duration of hospital stay. The ECT group more commonly had higher overall illness and aggression severity. Smoking was less frequent in the clozapine group. Baseline resistance/excitement symptom severity was significantly higher in the ECT group, while positive, negative, affect, disorganisation, and total symptom scores were not. Both interventions provided a significant reduction in PANSS scores with large effect sizes. CONCLUSION: Both ECT and clozapine yielded high effectiveness rates in adolescents with treatment-resistant schizophrenia/schizoaffective disorder. Youth receiving ECT were generally more activated than those who received clozapine.

Delineating gene-environment effects using virtual twins of patients treated with clozapine.

Studies that focus on individual covariates, while ignoring their interactions, may not be adequate for model-informed precision dosing (MIPD) in any given patient. Genetic variations that influence protein synthesis should be studied in conjunction with environmental covariates, such as cigarette smoking. The aim of this study was to build virtual twins (VTs) of real patients receiving clozapine with interacting covariates related to genetics and environment and to delineate the impact of interacting covariates on predicted clozapine plasma concentrations. Clozapine-treated patients with schizophrenia (N = 42) with observed clozapine plasma concentrations, demographic, environmental, and genotype data were used to construct VTs in Simcyp. The effect of increased covariate virtualization was assessed by performing simulations under three conditions: "low" (demographic), "medium" (demographic and environmental interaction), and "high" (demographic and environmental/genotype interaction) covariate virtualization. Increasing covariate virtualization with interaction improved the coefficient of variation (R2 ) from 0.07 in the low model to 0.391 and 0.368 in the medium and high models, respectively. Whereas R2 was similar between the medium and high models, the high covariate virtualization model had improved accuracy, with systematic bias of predicted clozapine plasma concentration improving from -138.48 ng/ml to -74.65 ng/ml. A high level of covariate virtualization (demographic, environmental, and genotype) may be required for MIPD using VTs.

Impact of NFIB and CYP1A variants on clozapine serum concentration-A retrospective naturalistic cohort study on 526 patients with known smoking habits.

Clinical response of clozapine is closely associated with serum concentration. Although tobacco smoking is the key environmental factor underlying interindividual variability in clozapine metabolism, recent genome-wide studies suggest that CYP1A and NFIB genetic variants may also be of significant importance, but their quantitative impact is unclear. We investigated the effects of the rs2472297 C>T (CYP1A) and rs28379954 T>C (NFIB) polymorphisms on serum concentrations in smokers and nonsmokers. The study retrospectively included 526 patients with known smoking habits (63.7% smokers) from a therapeutic drug monitoring service in Norway. Clozapine dose-adjusted concentrations (C/D) and patient proportions with subtherapeutic levels (<1070 nmol/L) were compared between CYP1A/NFIB variant allele carriers and homozygous wild-type carriers (noncarriers), in both smokers and nonsmokers. Clozapine C/D was reduced in patients carrying CYP1A-T and NFIB-C variants versus noncarriers, both among smokers (-48%; p < 0.0001) and nonsmokers (-35%; p = 0.028). Patients who smoke carrying CYP1A-T and NFIB-C variants had a 66% reduction in clozapine C/D versus nonsmoking noncarriers (p < 0.0001). The patient proportion with subtherapeutic levels was 2.9-fold higher in patients who smoke carrying NFIB-C and CYP1A-T variants versus nonsmoking noncarriers (p < 0.0001). In conclusion, CYP1A and NFIB variants have significant and additive impact on clozapine dose requirements for reaching target serum concentrations. Patients who smoke carrying the studied CYP1A and NFIB variants, comprising 2.5% of the study population, may need threefold higher doses to prevent risk of clozapine undertreatment. The results suggest that pre-emptive genotyping of NFIB and CYP1A may be utilized to guide clozapine dosing and improve clinical outcomes in patients with treatment-resistant schizophrenia.

Clozapine Blood Concentration Predicts Corrected QT-Interval Prolongation in Patients With Psychoses.

BACKGROUND: Corrected QT-interval (QTc) prolongation (QTP) is a rare but fatal adverse effect of antipsychotics. Clozapine is the only antipsychotic recommended for treatment of resistant schizophrenia; however, clozapine has been reported to cause QTP. We sought factors predictive of QTP in patients who had antipsychotic polypharmacy involving clozapine. We explored whether the clozapine blood concentration might predict QTP. METHODS: We included 133 patients with schizophrenia spectrum disorder who had antipsychotic polypharmacy involving clozapine. We used the χ2 and nonparametric tests to compare clozapine therapeutic drug monitoring (TDM) values and QTc-prolonged person (QTPP) status. Multivariate regression and mediator models were used to identify risk factors for QTPP status and QTP. RESULTS: In total, 111 patients were prescribed clozapine. The QTPP rates were 31.3% (20) for men and 23.2% (16) for women. Compared with the non-QTPP group, the QTPP group exhibited significantly higher daily dose of all antipsychotics including clozapine, a higher clozapine dose, and elevated clozapine and norclozapine TDM values. Furthermore, such patients were prescribed a greater number of antipsychotics. Multivariate logistic regression revealed that only the clozapine TDM value could be predictive factor for QTPP status (P = 0.018). A clozapine TDM value above the therapeutic range (>600 mg/dL) was associated with a high risk of QTPP status (adjusted odds ratio, 6.5; 95% confidence interval, 1.7-25.2; P = 0.006). The mediator model revealed that the clozapine TDM values completely mediated the association between the clozapine dose and the QTc interval. CONCLUSIONS: The clozapine blood concentration reliably predicts QTP in patients with clozapine use.