Clozapine Dose Research Articles

Association Between Clozapine Plasma Concentrations and Treatment Response: A Systematic Review, Meta-analysis and Individual Participant Data Meta-analysis.

Although therapeutic drug monitoring of clozapine is recommended, its optimisation is often adjusted only on the basis of dosage. The aim of this study was to assess the link between clozapine plasma concentrations and clinical response by a meta-analysis of published studies and by an individual participant data meta-analysis. We conducted a computerised search of bibliographic databases (EMBASE, PubMed, Clinical Trials, and Web of Science) to identify studies that assessed the relationship between clozapine serum or plasma concentrations and clinical efficacy. Using pooled data, we investigated the association between improvement of clinical outcome and clozapine or norclozapine plasma concentrations, the sum of clozapine and norclozapine plasma concentrations, and the coefficient of variation of clozapine plasma concentrations. Using available individual data, we assessed the relationship between clozapine plasma concentrations and clinical response (changes in the Brief Psychiatric Rating Scale score) and identified a threshold level for a favourable clinical response. Fifteen studies satisfied inclusion criteria. Our meta-analysis showed that responders had clozapine plasma concentrations that were, on average, 117 ng/mL higher than non-responders. The patients with plasma clozapine concentrations above the thresholds identified in each study had a higher likelihood of responding (odds ratio = 2.94, p < 0.001). Norclozapine plasma concentrations were not associated with a clinical response. The meta-analysis of individual data supported this result and confirmed the link between clozapine concentrations and a change in the Brief Psychiatric Rating Scale score and/or the probability of clinical response. Finally, with the analysis of the coefficient of variation of clozapine plasma concentrations, we found that a greater inter-individual fluctuation in plasma concentrations was associated with a loss of clinical response. Our work confirmed that, in contrast to clozapine doses, clozapine plasma concentrations were related to a favourable clinical response, with a mean difference between responders and non-responders of 117 ng/mL. A threshold for a treatment response of 407 ng/mL was determined, with a high discriminatory capacity,and a sensitivity and specificity of 71% and 89.1%, respectively.

The Potential Role of POR*28 and CYP1A2*F Genetic Variations and Lifestyle Factors on Clozapine and N-DesmethylClozapine Plasma Levels in Schizophrenia Patients

ABSTRACT Background Despite its advantages over other antipsychotics, for treatment-resistant schizophrenia, clinical use of Clozapine (CLZ) is challenging by its narrow therapeutic index and potentially life-threatening dose-related adverse effects. Research design and methods As the potential role in CLZ metabolism is assigned to CYP1A2 enzyme and consequently Cytochrome P450 oxidoreductase (POR) their genetic variations might help to determine CLZ levels in schizophrenia patients. For this purpose, 112 schizophrenia patients receiving CLZ were included in the current study. Plasma CLZ and N-desmethylclozapine (DCLZ) levels were analyzed by using HPLC and genetic variations were identified with the PCR-RFLP method. Results The patients’ CYP1A2 and POR genotypes seemed to not affect plasma CLZ and DCLZ levels whereas in the subgroup analysis, POR *28 genotype significantly influenced simple and adjusted plasma CLZ and DLCZ levels concerning smoking habit and caffeine consumption. Conclusions The findings of the present study highlight the importance of both genetic and non-genetic factors (smoking and caffeine consumption) for the individualization of the CLZ treatment. In addition to that, it suggests that the added utility of not only the CLZ metabolizing enzymes but also POR, which is crucial for proper CYP activity, to guide CLZ dosing might be useful for clinical decision-making.

Carbonized human hair derived carbon dots for detection of clozapine

Clozapine (CLZ) is known as the most effective antipsychotic medication for schizophrenia. However, low dosage or over dosage of CLZ is adverse to the treatment of Schizophrenia. Thus, it is necessary to develop effective detection method for CLZ. Recently, due to the advantages such as excellent optical properties, good photobleachability and sensitivity, carbon dots (CDs)-based fluorescent sensors for the detection of target analytes have drawn a great deal of attention. In this work, blue fluorescent CDs (Named as B-CDs) with quantum yield (QY) as high as 38% were obtained by using carbonized human hair as source material through one-step dialysis method for the first time. B-CDs showed obvious graphite-like structure with an average of 1.76 nm, containing abundant functional groups such as -C=O, amino N and C-N on the surface of carbon cores. Optical analysis showed that the B-CDs exhibited excitation-dependent emission property with maximum emission wavelength of 450 nm. Moreover, B-CDs were further applied as a fluorescence sensor to the detection of CLZ. The B-CDs based sensor exhibited a good quenching response by CLZ through the inner filter effect and static quenching mechanism with a limit of detection of 67 ng/mL, which was much lower than the minimal effective concentration in blood (0.35 μg/mL). Finally, to test the practical application value of the developed fluorescence method, the determination of the content of CLZ in tablets and the concentration in blood was carried out. Compared with the results of high-performance liquid chromatography (HPLC) method, it can be found that the constructed fluorescence detection method showed high accuracy and had great application potential in the detection of CLZ. Additionally, the results of cytotoxicity experiment showed that B-CDs had low cytotoxicity, which laid the foundation for the subsequent application of B-CDs in biological systems.

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

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. 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. 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). 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.

Prevalence and pattern of electroencephalographic changes associated with clozapine treatment: a cross-sectional study

BackgroundClozapine is a second-generation antipsychotic which is known to have superior efficacy as compared to other antipsychotics. It is particularly used in treatment-resistant schizophrenia (10–30%). However, its use is limited due to the serious side effect of inducing seizures which can occur at all doses. The purpose of our study was to analyse patients taking clozapine for any electroencephalographic (EEG) abnormalities. We undertook a cross-sectional study on 107 patients with a different diagnosis taking clozapine who visited the outdoor treatment facility of a tertiary care psychiatric diseases hospital in Kashmir. A 32-channel digital EEG was obtained and evaluated visually for any abnormalities in these patients. The data was tabulated and analysed using SPSS 23.0.ResultsEEG abnormalities were reported in 60.75% of patients receiving clozapine out of which slow waves and epileptiform activities were present in 48.60% and 30.84% of patients, respectively. Background slowing was often in the delta and theta ranges. Our study showed that there was a statistically significant relationship between the dose of clozapine and EEG abnormalities. Clinical seizure occurred in only one patient receiving clozapine 450 mg/day and was a smoker who had recently stopped smoking.ConclusionsEEG abnormalities occur frequently in clozapine-treated patients specifically those taking higher doses of clozapine. This calls for utilising EEG as a useful clinical investigation in these patients along with clinical monitoring of seizures especially in those taking higher doses of clozapine in order to hint towards early signs of clozapine toxicity. Caution needs to be taken in patients who are smokers and show a pattern of change in their smoking habits. Moreover, EEG abnormalities though frequently associated with clozapine are not reliable predictors of seizures. Therefore, anticonvulsants may not be routinely indicated in patients on clozapine even in the presence of epileptiform discharges.

Clinical impact of reducing the frequency of clozapine monitoring: controlled mirror-image cohort study.

To minimise infection during COVID-19, the clozapine haematological monitoring interval was extended from 4-weekly to 12-weekly intervals in South London and Maudsley NHS Foundation Trust. To investigate the impact of this temporary policy change on clinical and safety outcomes. All patients who received clozapine treatment with extended (12-weekly) monitoring in a large London National Health Service trust were included in a 1-year mirror-image study. A comparison group was selected with standard monitoring. The proportion of participants with mild to severe neutropenia and the proportion of participants attending the emergency department for clozapine-induced severe neutropenia treatment during the follow-up period were compared. Psychiatric hospital admission rates, clozapine dose and concomitant psychotropic medication in the 1 year before and the 1 year after extended monitoring were compared. All-cause clozapine discontinuation at 1-year follow-up was examined. Of 569 participants, 459 received clozapine with extended monitoring and 110 controls continued as normal. The total person-years were 458 in the intervention group and 109 in the control group, with a median follow-up time of 1 year in both groups. During follow-up, two participants (0.4%) recorded mild to moderate neutropenia in the intervention group and one (0.9%) in the control group. There was no difference in the incidence of haematological events between the two groups (IRR = 0.48, 95% CI 0.02-28.15, P = 0.29). All neutropenia cases in the intervention group were mild, co-occurring during COVID-19 infection. The median number of admissions per patient during the pre-mirror period remained unchanged (0, IQR = 0) during the post-mirror period. There was one death in the control group, secondary to COVID-19 infection. There was no evidence that the incidence of severe neutropenia was increased in those receiving extended monitoring.

The Nitric Oxide (NO) Donor Molsidomine Counteract Social Withdrawal and Cognition Deficits Induced by Blockade of the NMDA Receptor in the Rat

The deficiency of the gaseous molecule nitric oxide (NO) seems to be critically involved in the pathogenesis of schizophrenia. Thus, molecules that can normalize NO levels, as are NO donors, might be of utility for the medication of this psychiatric disease. The aim of the present study was to detect the ability of the NO donor molsidomine to reduce schizophrenia-like impairments produced by the blockade of the N-methyl-D-aspartate (NMDA) receptor in rats. Molsidomine's ability to attenuate social withdrawal and spatial recognition memory deficits induced by the NMDA receptor antagonist ketamine were assessed using the social interaction and the object location test, respectively. Further, the efficacy of the combination of sub-effective doses of molsidomine with sub-effective doses of the atypical antipsychotic clozapine in alleviating non-spatial recognition memory deficits was evaluated utilizing the object recognition task. Molsidomine (2 and 4 mg/kg) attenuated social withdrawal and spatial recognition memory deficits induced by ketamine. Co-administration of inactive doses of molsidomine (1 mg/kg) and clozapine (0.1 mg/kg) counteracted delay-dependent and ketamine-induced non-spatial recognition memory deficits. The current findings suggest that molsidomine is sensitive to glutamate hypofunction since it attenuated behavioral impairments in animal models mimicking the negative symptoms and cognitive deficits of schizophrenia. Additionally, the present results support the potential of molsidomine as an adjunctive drug for the therapy of schizophrenia.

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

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. 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. 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 12.0L 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. 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.

Brexpiprazole augmentation in a clozapine-resistant young schizophrenic patient: a successful case report.

IntroductionAlthough clozapine is considered the most effective drug for Treatment Resistant Schizophrenia (TRS), only 40% of patients treated will meet clinical response. Literature reviews and meta-analytic data offer no definite conclusions about the most effective clozapine augmentation strategies. Nevertheless, it has been suggested that the lack of evidence should not discourage clinicians from trying out new strategies in individual patients. Brexpiprazole is a novel 5-HT and DA modulator antipsychotic that exhibits partial agonism to D2/D3 and 5HT1A receptors, antagonism to 5HT2A and α-1B/2C receptors and represents a promising new drug in the pharmacotherapy of schizophrenia for both acute and maintenance treatment. In current literature there is no evidence of experiences in brexpiprazole augmentation for clozapine resistant patients.ObjectivesThis case report describes a successful clinical experience of brexpiprazole augmentation in a complicated case of clozapine resistant paranoid schizophrenia with consistent negative symptoms, the clinical evolution and metabolic improvement consequent to this therapy combination.MethodsIn a 27 male TRS patient, sequentially treated with adequate doses of risperidone, cariprazine, aripiprazole and olanzapine monotherapy, prescribed for adequate time, clozapine treatment was started, with a gradual titration from 25 to 300 mg/day, without significant clinical response on both positive and negative symptoms. Successively was introduced fluoxetine, from 10 to 30 mg/day, with no relevant clinical improvement. After 2 months of pharmacological stabilization with clozapine and fluoxetine described dosages, brexpiprazole was introduced starting from 1 mg/day and rapidly increasing till 4 mg/day.ResultsAfter 6 weeks of treatment, PANSS positive and negative subscales showed a significant decrease, respectively from 28 to 17 and from 42 to 20, while general psychopathology subscale decreased from 66 to 34. Negative sub-items with major improvement were those regarding blunted affect, emotional withdrawal, poor rapport, and passive/apathetic social withdrawal. Brexpiprazole augmentation also allowed to slowly decrease (in 6 months) clozapine dose till actual 150 mg/day, with a significant improvement in general tolerability and a slow decline in metabolic parameters (BMI from 36.5 to 30.3; fasting glucose from 112 to 92 mg/dL; total cholesterol from 248 to 182 mg/dL; total triglycerides from 392 to 198 mg/dL).ConclusionsIn this case report brexpiprazole augmentation in a clozapine resistant young schizophrenic patient was an effective strategy with significant symptoms improvement, in particular in PANSS general psychopathology and PANSS negative subscales. The consequent clozapine dose reduction contribute to the slow decrease in metabolic parameters considered.Disclosure of InterestNone Declared

Hepatotoxicity of Clozapine : Case report and brief Review

IntroductionClozapine is an effective Atypical antipsychotic used in the treatment of resistant schizophrenia .However it can induce liver dysfunction from a simple transient asymptomatic cytolisis (30 to50 %) toa serious fulminant liver failure (0.001 %).ObjectivesTo show the heptotoxicity potential of Clozapine and adress the importance of monitoring the liver function tests in clozapine titration to prevent sever conditionsMethodsA case report of a fifty-year old Tunisian male patient diagnosed with resistant schizophrenia who developed a hepatototoxicity under a low dose of clozapine within five days of treatment .ResultsMr F is a 50 year old patient diagnosed with schizophrenia in 2018 . He had received various antypical and typical antipsychotic treatments including ( Haloperidol , Risperidone , Amisulpride , Olanzapine ) at effective doses and minimal periods of six weeks . He had no history of systemic diseases or substance use disorder . He smokes 10 cigarettes a day . He had a history of hepatotoxicity on olanzapine. These medications have failed to resolve the persecutory delusion and auditory hallucinations , and the trial of clozapine was institued . Baseline examination and laboratory tests were normal . The previous antipsychotic medication was not continued and a dose of 25 mg clozapine was administred . A marking drowsiness was present in the fisrt days , so we decided to keep the same dose . Five days later , he had high levels of Liver function test (LFT) : Elevated aspartate ( 5 times above normal) and alanine aminotransferase levels (4 times above normal ) , white blood cell count and bilirubine levels were normal . He had no fever or jaundice . The abdominal examination showed a mild sensiblity in the right upper quadrant . Clozapine was immediatly discontinuated . 24 hours later LFT continued to escalate to 5 times greater then normal . Then it decreased continueoslyConclusionsClozapine has a potential of hepatotoxicity even at lower dose . Screening liver function tests must be integrated in survey recommendations of clozapine treatment . Further researches must be conducted to understand the mechanism of this side effect in order to avoid sever conditions .Disclosure of InterestNone Declared

Reflections on the Lack of Consideration of Ethnic Ancestry to Stratify Clozapine Dosing.

This review article argues against trusting standard clozapine references, including the US package insert, because they do not include advances in the sciences of pharmacokinetics and pharmacovigilance and ignore the effects of ethnic ancestry on therapeutic dosing. The minimum therapeutic dose leading to the minimum therapeutic concentration of 350 ng/mL in serum/plasma can be used to compare individuals/groups with treatment-resistant schizophrenia. The US clozapine package insert recommends targeting doses of 300-450 mg/day and, subsequently, increments of up to 100 mg with a maximum dose of 900 mg/day. Ethnic ancestry is defined by DNA ancestry group. Asians (people with ancestry ranging from Pakistan to Japan) and Indigenous Americans are similar in clozapine dosing; their average clozapine minimum therapeutic dose ranged from 166 mg/day (female non-smokers) to 270 mg/day (male smokers). For those with European ancestry, average clozapine minimum therapeutic doses ranged from 236 mg/day (female non-smokers) to 368 mg/day (male smokers). Based on limited studies, Black (African sub-Saharan ancestry) patients may be treated with typical US doses (300-600 mg/day), assuming no poor metabolism (PM) status. Ancestry's impact on clozapine lethality in four countries is discussed (two countries with highly homogenous populations, Denmark and Japan, and two countries with increasingly heterogenous populations due to immigration, Australia and the UK). An international guideline with 104 authors from 50 countries/regions was recently published, providing 6 personalized clozapine titration schedules for adult inpatients (3 ancestry groups and PM/non-PM schedules) and recommending c-reactive protein monitoring at baseline and weekly for 4 weeks.

Feasibility and Effect of Increasing Clozapine Plasma Levels in Long-Stay Patients With Treatment-Resistant Schizophrenia

It is unknown whether increasing the clozapine plasma level to 400, 750, or even 1000 ng/mL is a feasible and effective strategy in patients with treatment-resistant schizophrenia (TRS). We investigated this in long-stay patients with TRS. In long-stay TRS patients, doses of clozapine were increased gradually to reach target plasma levels of 400, 750, or 1000 ng/mL, depending on the clinical response and tolerability. After an effective or tolerated level was reached, positive and negative syndrome scale scores were evaluated after 3 months and 1 year. Twenty-eight patients were included. Overall, 54% of the patients, and especially patients 60 years and older, could not achieve one of the clozapine target levels because of adverse effects. Three physically vulnerable patients died, probably not directly related to clozapine use. Although only 21% of patients achieved a more than 20% reduction in total symptoms at the 1-year follow-up, the mean severity of positive symptoms decreased from 18.18 to 15.10 ( P < 0.01). The largest decrease in positive symptoms was seen in TRS patients who achieved a plasma level of 750 ng/mL of clozapine. Most TRS patients older than 60 years could not tolerate high clozapine levels and so this should not be attempted in older or otherwise physically vulnerable patients. Increasing clozapine levels to approximately 750 ng/mL in middle-aged patients with longstanding TRS may modestly reduce the severity of positive symptoms and improve the response rate.

Is Clozapine-induced Weight Gain Dose-dependent? Results From a Prospective Cohort Study.

Antipsychotic-induced metabolic adverse effects are risk factors for cardiometabolic comorbidities. Whether dose lowering could mitigate such effects remains unclear. The present study aims to investigate the associations between clozapine doses and modifications of weight, blood pressure, blood glucose, and lipid levels. Linear mixed-effects models of weight changes over 1 year and of variations of other metabolic parameters over 4 months were applied to a prospective cohort of 115 patients. Age- and sex-stratified analyses of weight changes were also performed. Each 100 mg dose increment of clozapine was associated on average with a +0.48% weight increase (P = .004) over 1 year of treatment. Weight increase was greater for treatment duration ≤3 vs >3 months (+0.84% and +0.47% per month, respectively, P < .001), with a significant association with the dose for durations >3 months (+0.54%, P = .004) and a trend for durations ≤3 months (+0.33%, P = .075). Dose increments of 100 mg were also associated with weight increases of +0.71% among adults (P = .001), +1.91% among the elderly (P < .001) and +1.32% among men (P < .001) with no associations among women (P = .62). Among young adults, weight change was positively associated with doses ≤300 mg/day (+2.19% per 100 mg, P = .001), whereas no association was found with doses >300 mg/day (P = .60). No significant effect of clozapine dose on other metabolic parameters was found. This study reports a modest effect of clozapine dose increases on weight gain over 1 year with differences among age categories and sexes and no dose effect on other metabolic parameters over 4 months.

Lower sertraline plasma concentration in patients co-medicated with clozapine-Implications for pharmacological augmentation strategies in schizophrenia.

Augmentation of antipsychotic treatment with antidepressants represents a common and beneficial treatment strategy in patients suffering from schizophrenia. Combining clozapine and the selective serotonin reuptake inhibitor (SSRI) sertraline represents a clinically important strategy in patients with therapy-resistant schizophrenia, but there is limited knowledge about mutual pharmacokinetic interactions. In the present study, we assessed the impact of clozapine on sertraline plasma concentrations. Based on a therapeutic drug monitoring (TDM) database, sertraline plasma concentrations were compared between two groups: patients receiving a combined treatment with sertraline and clozapine (N= 15) and a matched control group receiving sertraline but no clozapine (N= 17). Group differences with respect to raw and dose-adjusted concentrations were assessed using nonparametric tests. Comedication with clozapine was associated with 67% lower median sertraline plasma concentrations (16 vs. 48 ng/mL; p= .022) and 28% lower median dose-adjusted plasma concentrations (C/D; 0.21 vs. 0.29 (ng/mL)/(mg/day); p= .049) as compared to the control group. Scatter plots revealed a complex relationship between the dosage of clozapine and dose-adjusted sertraline concentrations composed of an initial decrease at clozapine doses below 300 mg, an increase between 300 and 600 mg and a final decrease at 800 mg which was best modeled by a third order polynomial term. Cotreatment with clozapine may lead to reduced sertraline plasma concentrations which may be explained by clozapine-induced gastrointestinal hypo-mobility already present at low doses and cytochrome P450 3A4 inducing properties at high clozapine doses. For this drug combination, clinicians should consider TDM to confirm therapeutically effective plasma concentrations of sertraline.

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

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. 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. 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. 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. UK Academy of Medical Sciences, UK Medical Research Council, and European Commission.

Opposing effects of clozapine and brexpiprazole on β-aminoisobutyric acid: Pathophysiology of antipsychotics-induced weight gain

Clozapine is one of the most effective antipsychotics and has the highest risk of weight gain and metabolic complications; however, the detailed pathophysiology of its clinical action and adverse reactions remains to be clarified. Therefore, the present study determined the chronic effects of clozapine (high risk of weight gain) and brexpiprazole (relatively low risk of weight gain) on intracellular and extracellular levels of β-aminoisobutyric acid (BAIBA) enantiomers, which are endogenous activators of AMP-activated protein kinase (AMPK). L-BAIBA is the dominant BAIBA enantiomer in the rat hypothalamus and cultured astrocytes, whereas L-BAIBA accounts for only approximately 5% of the total plasma BAIBA enantiomers. L-BAIBA displayed GABAB receptor agonistic action in the extracellular space and was released through activated astroglial hemichannels, whereas in the intracellular space, L-BAIBA activated AMPK signalling. Chronic administration of the effective doses of clozapine increased intracellular and extracellular levels of L-BAIBA in the hypothalamus and cultured astrocytes, whereas that of brexpiprazole decreased them. These results suggest that enhancing hypothalamic AMPK signalling by increasing intracellular L-BAIBA levels is, at least partially, involved in the pathophysiology of clozapine-induced weight gain and metabolic complications.

Clozapine: Dose, Sex, Ethnicity, Smoking Habit, Age, Body Weight, and Plasma Clozapine and N-Desmethylclozapine (Norclozapine) Concentrations in Clinical Practice.

Guidance on clozapine dosing in treatment refractory schizophrenia is based largely on data from young adult male White patients. This study aimed to audit the plasma clozapine and N-desmethylclozapine (norclozapine) concentrations attained in male and female patients of different ethnicity and smoking habit. The effect of dose, sex, ethnicity, age, body weight, and smoking habit on plasma clozapine and norclozapine concentrations were studied using data from a therapeutic drug monitoring service, 1993 to 2017. There were 371,610 samples (48,098 patients, 32,855 male). Ethnicity was recorded for 763 Afro-Caribbean, 536 Asian, and 7940 White patients. Males were prescribed significantly higher median doses than females but attained significantly lower median plasma clozapine and norclozapine concentrations. Asian and Afro-Caribbean males were prescribed significantly lower and higher median doses, respectively, than White males but attained significantly higher and lower median plasma clozapine and norclozapine concentrations, respectively. Data from 78,431 samples (23,516 patients) were analyzed using a linear mixed model. The predicted dose to attain a predose plasma clozapine concentration of 0.35 mg/L in a nonsmoking White male aged 40 years, with weight of 70 kg, and plasma clozapine-norclozapine ratio of 1.32 was 344 mg/d (95% confidence interval, 227-526 mg/d). The predicted dose was 33% higher and 20% lower in otherwise analogous Afro-Caribbean and Asian patients, respectively. In all cases, the predicted dose was increased by 36% in smokers and decreased by 22% in females. Research is needed to further investigate the complex relationships between dose, sex, ethnicity, plasma clozapine and norclozapine concentrations, and clinical outcome such as weight gain.

Therapeutic monitoring of plasma clozapine andN-desmethylclozapine (norclozapine): practical considerations

SUMMARYClozapine dose assessment in treatment-refractory schizophrenia is complicated. There is a narrow margin between an effective and a potentially toxic dose and wide inter-individual variation in clozapine metabolic capacity. Moreover, factors such as changes in smoking habit, infection/inflammation, co-prescription of certain drugs, notably fluvoxamine, and age alter the dose requirement within individuals. Therapeutic drug monitoring (TDM) of plasma clozapine andN-desmethylclozapine (norclozapine) can help assess adherence, guide dosage and guard against toxicity. This article gives an overview of clozapine pharmacokinetics and factors affecting clozapine dose requirements. It then outlines the procedures and processes of clozapine TDM, from taking the blood sample for laboratory assay or point-of-contact (finger-prick) testing (POCT) to interpreting and acting on the results.

Meta-analysis of clozapine and insomnia in schizophrenia

IntroductionInsomnia commonly occurs in schizophrenia, and insomnia is associated with suicide risk. Clozapine has anti-suicidal properties and beneficial effects on sleep. We performed a meta-analysis of insomnia in randomized controlled trials (RCTs) of patients with schizophrenia treated with clozapine. We hypothesized that compared to clozapine there is an increased odds of insomnia in patients treated with other antipsychotics. MethodsWe systematically searched PubMed, PsycINFO, and Web of Science databases. We included RCTs, in English, with data on insomnia in patients with schizophrenia treated with clozapine versus other antipsychotics. Data were pooled using a random effects model. ResultsEight RCTs (1952 patients: 922 on clozapine and 1030 on other antipsychotics) met inclusion criteria. Patients treated with other antipsychotics versus clozapine had a significant increased odds of insomnia (22.3 % versus 12.4 %, OR = 2.20, 95 % CI = 1.64–2.94, p < 0.01). Olanzapine, quetiapine, risperidone, and ziprasidone were each associated with significant increased odds of insomnia compared to clozapine. In meta-regression analyses, clozapine dose, publication year, sex, trial duration, and study quality score were unrelated to the association; however, there was a significant association with age. The observed ORs for insomnia from RCTs were almost perfectly correlated with reported ORs from pharmacovigilance data. ConclusionClozapine is associated with significantly less insomnia compared to other antipsychotics. Findings provide additional evidence for improvement in sleep as a potential pathway underlying clozapine's anti-suicidal properties. A greater mechanistic understanding of this association is needed.

Japanese patients need slower, personalized clozapine titrations: A comment on the case described by Kikuchi et al.

Japanese patients need slower, personalized clozapine titrations: A comment on the case described by Kikuchi et al.