Plasma clozapine, norclozapine, and the clozapine:norclozapine ratio in relation to prescribed dose and other factors: data from a therapeutic drug monitoring service, 1993-2007

Exploring low clozapine C/D ratios, inverted clozapine-norclozapine ratios and undetectable concentrations as measures of non-adherence in clozapine patients: A literature review and a case series of 17 patients from 3 studies

BACKGROUND

Up to 1/2 of outpatients prescribed clozapine may be partially/fully non-adherent, based on therapeutic drug monitoring (TDM). Three indices for measuring partial/full non-adherence are proposed a: 1) clozapine concentration/dose (C/D) ratio which drops to half or more of what is expected in the patient; 2) clozapine/norclozapine ratio that becomes inverted; and 3) clozapine concentration that becomes non-detectable.

METHODS

These 3 proposed indices are based on a literature review and 17 cases of possible non-adherence from 3 samples: 1) an inpatient study in a Chinese hospital, 2) an inpatient randomized clinical trial in a United States hospital, and 3) and a Uruguayan outpatient study.

RESULTS

The first index of non-adherence is a clozapine C/D ratio which is less than half the ratio corresponding to the patient's specific ancestry group and sex-smoking subgroup. Knowing the minimum therapeutic dose of the patient based on repeated TDM makes it much easier to establish non-adherence. The second index is inverted clozapine/norclozapine ratios in the absence of alternative explanations. The third index is undetectable concentrations. By using half-lives, the chronology of the 3 indices of non-adherence was modeled in two patients: 1) the clozapine C/D ratio dropped to ≥1/2 of what is expected from the patient (around day 2); 2) the clozapine/norclozapine ratio became inverted (around day 3); and 3) the clozapine concentration became undetectable by the laboratory (around days 9-11).

CONCLUSION

Prospective studies should further explore these proposed clozapine indices in average patients, poor metabolizers (3 presented) and ultrarapid metabolizers (2 presented).

Clozapine ultrarapid metabolism during weak induction probably exists but requires careful diagnosis. A literature review, five new cases and a proposed definition

During weak induction (from smoking and/or valproate co-prescription), clozapine ultrarapid metabolizers (UMs) need very high daily doses to reach the minimum therapeutic concentration of 350 ng/ml in plasma; clozapine UMs need clozapine doses higher than: 1) 900 mg/day in patients of European/African ancestry, or 2) 600 mg/day in those of Asian ancestry. Published clozapine UMs include 10 males of European/African ancestry, mainly assessed with single concentrations. Five new clozapine UMs (two of European and three of Asian ancestry) with repeated assessments are described. A US double-blind randomized trial included a 32-year-old male smoking two packages/day with a minimum therapeutic dose of 1,591 mg/day from a single TDM during open treatment of 900 mg/day. In a Turkish inpatient study, a 30-year-old male smoker was a possible clozapine UM needing a minimum therapeutic dose of 1,029 mg/day estimated from two trough steady-state concentrations on 600 mg/day. In a Chinese study, three possible clozapine UMs (all male smokers) were identified. The clozapine minimum therapeutic dose estimated with trough steady-state concentrations >150 ng/ml was: 1) 625 mg/day, based on a mean of 20 concentrations in Case 3; 2) 673 mg/day, based on a mean of 4 concentrations in Case 4; and 3) 648 mg/day, based on a mean of 11 concentrations in Case 5. Based on these limited studies, clozapine UMs during weak induction may account for 1-2% of clozapine-treated patients of European ancestry and <1% of those of Asian ancestry. A clozapine-to-norclozapine ratio <0.5 should not be used to identify clozapine UMs.

Clozapine metabolism and cardiotoxicity: A prospective longitudinal study

BACKGROUND

Clozapine-induced myocarditis and cardiomyopathy are difficult to detect clinically and may be fatal if not detected early. The current/routine biomarkers for clozapine-induced myocarditis are non-specific indicators of inflammation (C-reactive protein) or cardiomyocyte damage (troponins I and T) that lack sensitivity, and for which changes often arise too late to be clinically useful.

METHODS

The Clozapine Safety Study was a prospective, longitudinal, observational study to determine what, if any, the plasma concentrations of clozapine, N-desmethylclozapine, and clozapine-N-oxide in patients contribute to cardiotoxicity. Samples were collected and analysed using liquid chromatography mass spectrometry over a 41-month period from patients in the Auckland District Health Board.

RESULTS

Sixty-seven patients were included. Six patients were diagnosed with myocarditis; none were diagnosed with cardiomyopathy in the study period. In patients not undergoing dose titration, clozapine biotransformation may shift to the N-oxide pathway rather than the N-desmethyl pathway with increasing dose. During dose titration, the timeframe in which myocarditis occurs, the rate of increase in the plasma concentration of clozapine-N-oxide, as well as the ratio of N-oxidation relative to N-desmethylation, were significantly higher in patients diagnosed with myocarditis.

CONCLUSIONS

The assessment of clozapine-N-oxide formation, and N-oxidation relative to N-desmethylation ratios during treatment, may help identify a biomarker to aid the early detection of patients at risk of developing clozapine-induced cardiotoxicity.

Clinical and pharmacological factors influencing serum clozapine and norclozapine levels

Background

Clozapine (CLO) is a very effective antipsychotic, whose use is associated with dose-dependent risk of complications. Due to high interindividual variability in CLO metabolism, there is a need to identify factors affecting the blood concentrations of CLO and its active metabolite, norclozapine (NCLO).

Methods

A total of 446 blood samples (collected from 233 women and 213 men, aged from 18 to 77 years) were included in this study and analyzed for CLO and NCLO concentrations. The patients were treated at a psychiatric hospital in Warsaw in the years 2016-2021. Serum CLO and NCLO concentrations were determined with high-performance liquid chromatography coupled to UV.

Results

The following factors were shown to increase serum CLO and NCLO levels: higher CLO dose (p < 0.001), female sex (p < 0.001), nonsmoker status (p < 0.001), the use of more than two additional psychotropic drugs (only in the case of CLO; p = 0.046), concomitant use of beta-blockers (for CLO p = 0.049; for NCLO p < 0.001), and older age (for CLO p < 0.001; for NCLO p = 0.011). Despite the use of CLO at daily doses within the recommended range (200-450 mg), the evaluated serum CLO and NCLO levels were within the therapeutic ranges in only 37% and 75% of cases, respectively, with 5.6% of cases exceeding the CLO toxicity threshold.

Discussion

The use of CLO at recommended doses does not guarantee achieving therapeutic concentrations of CLO or NCLO. Women and nonsmokers were at the highest risk of having toxic CLO levels.

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.

High rates of myocarditis with clozapine in the Hunter region of Australia

OBJECTIVE

To study the causes of clozapine treatment discontinuation and measure clozapine-induced myocarditis (CIM) rates in an Australian region, to compare the observed rates of CMI with reports from Australia and the world, and discuss factors related to CIM incidence rates in the region.

METHODS

The study is a retrospective clinical audit of 327 patients prescribed clozapine. All patients were monitored by the mandatory CIM monitoring protocol for the first six weeks of treatment. The validity of a diagnosis of CIM was assessed using six criteria. Socio-demographic and clinical factors and clozapine prescription practices were analysed for their association with CIM. The study could not examine co-existing medical illness, co-prescribed psychotropic medication, genetics, and environmental factors.

RESULTS

CIM occurred in 9.8 % of the cohort after a mean treatment duration of 19.5 days. The diagnosis of CIM was considered valid in all cases. Gender, age at the start of treatment, ethnicity, cumulative clozapine dose, dose titration, and clozapine/norclozapine ratio were unrelated to CIM.

CONCLUSION

The CIM rate in the Hunter region was higher than in the rest of Australia and the world and increased after adopting the monitoring protocol. Over-diagnosis, patient's age and gender, ethnicity, cumulative clozapine dose, dosing titration, and clozapine metabolism rate were unrelated to the high occurrence rates. The possible role of comorbid illnesses, co-prescribed psychiatric medications, genetic, and environmental factors in the etiology of CIM requires further study. The reasons underlying the high rates of CIM in the Hunter region need further exploration.

A retrospective study of clozapine and norclozapine concentration in patients with schizophrenia: Data from the Therapeutic Drug Monitoring Service, 2019-2022

OBJECTIVE

The aim of this research was to assess the therapeutic drug monitoring (TDM) of clozapine (CLO) and norclozapine (NCLO).

METHODS

TDM results of CLO and NCLO in patients obtained from the Xi'an Mental Health Center were retrospectively analyzed.

RESULTS

TDM of CLO and NCLO was typically conducted only once in the majority of patients, particularly those receiving outpatient care. The CLO plasma concentrations were higher in inpatients and female patients. The interquartile (25th-75th) CLO concentrations ranged from 129.83 to 397.53 ng/mL, nearly 68.63% of the samples had subtherapeutic concentrations (<350 ng/mL). Receiver operating characteristic curve analysis showed that inpatients achieved the therapeutic level concentration of 350-600 ng/mL when their daily CLO dose was > 125 mg.

CONCLUSIONS

It was surprising to find such a large number of patients with CLO levels below the therapeutic range, there is still a window of improvement for optimizing pharmacological treatments in clinical practice.

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.

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.

Predicting clozapine dose required to achieve a therapeutic plasma concentration - A comparison of a population algorithm and three algorithms based on gene variant models

BACKGROUND

Clozapine is the most effective antipsychotic but requires careful titration to therapeutic blood levels. Methods to predict therapeutic doses are based on population data.

AIMS

We aimed to construct a model based on genetic variants which accurately predicted plasma levels for clozapine.

METHOD

We measured clozapine plasma levels in patients on a stable dose of clozapine who were known to be fully compliant. Measured plasma levels were adjusted for sampling time and dose. Hepatic enzyme variants were analysed and models were constructed to predict the required dose. These predictions were compared with a standard population-based algorithm.

RESULTS

We measured plasma clozapine concentrations in 18 adherent patients on stable doses of clozapine and recorded the exact timing of sampling. For the algorithm-predicted dose, the mean difference was -49.9 mg/day ((SD 155.9), r = 0.36) from the actual dose required to give a plasma concentration of 0.35 ng/ml. The gene variant activity score predicted a dose for which the mean difference was -43.5 mg/day ((SD 140.1), r = 0.55). For the gene variant activity score with omeprazole correction predicted dose, the mean difference was -31.0 mg/day ((SD 140.8), r = 0.54), and with the gene variant CYP1A2 inducibility predicted dose the mean difference was 44.9 mg/day ((SD 160.8), r = 0.32).

CONCLUSION

Our gene variant activity score with omeprazole correction gave the best estimate of the clozapine dose required to achieve a minimum therapeutic plasma concentration. The use of this model will allow safer titration of clozapine and may reduce the need for plasma-level monitoring during titration.

Effects of smoking cessation on plasma clozapine concentrations in male patients with schizophrenia during the COVID-19 pandemic

Introduction

This study aimed to investigate the effect of smoking cessation on plasma clozapine (CLO) concentrations in long-term hospitalized Chinese male patients with schizophrenia treated with CLO during the COVID-19 pandemic.

Methods

Therapeutic drug monitoring (TDM) data for CLO were collected at Beijing HuiLongGuan Hospital between December 1, 2019 (before smoking cessation) and January 31, 2020 (after smoking cessation) in this retrospective study. Fifty-three male smokers and inpatients with schizophrenia who were treated with CLO were included. Plasma concentrations of CLO were measured using high-performance liquid chromatography-tandem mass spectrometry. The fagerstrom test for nicotine dependence (FTND) was used to assess smoking behavior.

Results

The plasma CLO concentrations and dose-corrected plasma CLO concentrations were significantly increased by 29.3 and 23.5%, respectively, after smoking cessation.

Discussion

The results suggested that clinicians and pharmacists should adjust the CLO dose based on changes in smoking status in patients stabilized with CLO during the COVID-19 pandemic. Careful TDM for CLO should be performed prior to dose adjustment，to reduce the increased risk of smoking cessation induced side effects, especially for older patients receiving multiple medications.

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

BACKGROUND

Guidance on clozapine dosing in treatment refractory schizophrenia is based largely on data from young adult male White patients.

AIM

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.

METHOD

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.

RESULTS

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.

CONCLUSIONS

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 and N-desmethylclozapine (norclozapine): practical considerations

Clozapine 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 and N-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.

Genomic Stratification of Clozapine Prescription Patterns Using Schizophrenia Polygenic Scores

BACKGROUND

Treatment-resistant schizophrenia affects approximately 30% of individuals with the disorder. Clozapine is the medication of choice in treatment-resistant schizophrenia, but optimizing administration and dose titration is complex. The identification of factors influencing clozapine prescription and response, including genetics, is of interest in a precision psychiatry framework.

METHODS

We used linear regression models accounting for demographic, pharmacological, and clinical covariates to determine whether a polygenic risk score (PRS) for schizophrenia would be associated with the highest dose recorded during clozapine treatment. Analyses were performed across 2 independent multiancestry samples of individuals from a UK patient monitoring system, CLOZUK2 (n = 3133) and CLOZUK3 (n = 909), and a European sample from a Norwegian therapeutic drug monitoring service (n = 417). In a secondary analysis merging both UK cohorts, logistic regression models were used to estimate the relationship between schizophrenia PRSs and clozapine doses classified as low, standard, or high.

RESULTS

After controlling for relevant covariates, the schizophrenia PRS was correlated with the highest clozapine dose on record for each individual across all samples: CLOZUK2 (β = 12.22, SE = 3.78, p = .001), CLOZUK3 (β = 12.73, SE = 5.99, p = .034), and the Norwegian cohort (β = 46.45, SE = 18.83, p = .014). In a secondary analysis, the schizophrenia PRS was associated with taking clozapine doses >600 mg/day (odds ratio = 1.279, p = .006).

CONCLUSIONS

The schizophrenia PRS was associated with the highest clozapine dose prescribed for an individual in records from 3 independent samples, suggesting that the genetic liability for schizophrenia might index factors associated with therapeutic decisions in cohorts of patients with treatment-resistant schizophrenia.

Development and validation of a risk prediction nomogram for disposition of acute clozapine intoxicated patients to intensive care unit

BACKGROUND

Clozapine is an atypical antipsychotic drug used for the treatment of refractory schizophrenia. It is reported as the most toxic in its class. Using serum clozapine level as a severity indicator is doubtful and unfeasible, particularly in low resourced countries.

METHODS

This is an extended two-phase retrospective study that utilized medical records of patients diagnosed with acute clozapine intoxication and admitted to Tanta University Poison Control Center, Egypt during the past 6 years. Two hundred and eight medical records were used to establish and validate a nomogram for predicting the need for intensive care unit (ICU) admission in acute clozapine intoxicated patients.

RESULTS

A reliable simple bedside nomogram was developed and proved its significant ability to predict the need for ICU admission, with an area under the curve (AUC) of 83.9% and 80.8% accuracy. It encompassed the age of admitted patients (AUC = 64.8%, p = .003), respiratory rate (AUC = 74.7%, p < .001), O₂ saturation (AUC = 71.7%, p < .001), and random blood glucose level upon admission (AUC = 70.5%, p < .001). External validation of the proposed nomogram showed a high AUC (99.2%) with an overall accuracy of 96.2%.

CONCLUSION

There is a need to develop a reliable objective tool predicting the severity and need for ICU admission in acute clozapine intoxication. The proposed nomogram is a substantially valuable tool to estimate ICU admission probabilities among patients with acute clozapine intoxication and will help clinical toxicologists make rapid decisions for ICU admission, especially in countries with low resources.

Second to none: rationale, timing, and clinical management of clozapine use in schizophrenia

Despite its enduring relevance as the single most effective and important evidence-based treatment for schizophrenia, underutilization of clozapine remains considerable. To a substantial degree, this is attributable to a reluctance of psychiatrists to offer clozapine due to its relatively large side-effect burden and the complexity of its use. This underscores the necessity for continued education regarding both the vital nature and the intricacies of clozapine treatment. This narrative review summarizes all clinically relevant areas of evidence, which support clozapine's wide-ranging superior efficacy - for treatment-resistant schizophrenia (TRS) and beyond - and make its safe use eminently feasible. Converging evidence indicates that TRS constitutes a distinct albeit heterogeneous subgroup of schizophrenias primarily responsive to clozapine. Most importantly, the predominantly early onset of treatment resistance and the considerable decline in response rates associated with its delayed initiation make clozapine an essential treatment option throughout the course of illness, beginning with the first psychotic episode. To maximize patients' benefits, systematic early recognition efforts based on stringent use of TRS criteria, a timely offer of clozapine, thorough side-effect screening and management as well as consistent use of therapeutic drug monitoring and established augmentation strategies for suboptimal responders are crucial. To minimize permanent all-cause discontinuation, re-challenges after neutropenia or myocarditis should be considered. Owing to clozapine's unique efficacy, comorbid conditions including substance use and most somatic disorders should not dissuade but rather encourage clinicians to consider clozapine. Moreover, treatment decisions need to be informed by the late onset of clozapine's full effects, which for reduced suicidality and mortality rates may not even be readily apparent. Overall, the singular extent of its efficacy combined with the high level of patient satisfaction continues to distinguish clozapine from all other available antipsychotics.

Towards Precision Dosing of Clozapine in Schizophrenia: External Evaluation of Population Pharmacokinetic Models and Bayesian Forecasting

BACKGROUND

Therapeutic drug monitoring and treatment optimization of clozapine are recommended, owing to its narrow therapeutic range and pharmacokinetic (PK) variability. This study aims to assess the clinical applicability of published population PK models by testing their predictive performance in an external data set and to determine the effectiveness of Bayesian forecasting (BF) for clozapine treatment optimization.

METHODS

Available models of clozapine were identified, and their predictive performance was determined using an external data set (53 patients, 151 samples). The median prediction error (PE) and median absolute PE were used to assess bias and inaccuracy. The potential factors influencing model predictability were also investigated. The final concentration was reestimated for all patients using covariates or previously observed concentrations.

RESULTS

The 7 included models presented limited predictive performance. Only 1 model met the acceptability criteria (median PE ≤ ±20% and median absolute PE ≤30%). There was no difference between the data used for building the models (therapeutic drug monitoring or PK study) or the number of compartments in the models. A tendency for higher inaccuracy at low concentrations during treatment initiation was observed. Heterogeneities were observed in the predictive performances between the subpopulations, especially in terms of smoking status and sex. For the models included, BF significantly improved their predictive performance.

CONCLUSIONS

Our study showed that upon external evaluation, clozapine models provide limited predictive performance, especially in subpopulations such as nonsmokers. From the perspective of model-informed prediction dosing, model predictability should be improved using updating or metamodeling methods. Moreover, BF substantially improved model predictability and could be used for clozapine treatment optimization.

Pharmacokinetic interactions between clozapine and valproic acid in patients with treatment-resistant schizophrenia: Does UGT polymorphism affect these drug interactions?

The combination of valproic acid (VPA) and clozapine (CLZ) is regularly prescribed for augmentation therapy in treatment resistant schizophrenia. The VPA has been shown to reduce norclozapine (NCLZ) plasma levels, but the mechanism of this interaction remains unknown. The aim of this study is to examine the differences between patients treated with CLZ and patients treated with CLZ plus VPA. For it, various factors have been evaluated. The study was based on plasma samples from CLZ and CLZ plus VPA treated patients (n = 61) subjected to routine therapeutic drug monitoring considering clinical data, smoking status, daily dose of CLZ and VPA, concomitant medications, albumin, and renal and hepatic function. Genotyping of polymorphisms of CYP1A2, CYP3A4/5, CYP2C19, ABCB1, UGT2B10 and CYP2C19 were performed by real time PCR. CYP2D6 were genotyped using competitive allele-specific PCR and by a long PCR based method. Plasma CLZ and NCLZ concentrations were measured by Liquid Chromatography-Tandem masses (LC-MS/MS) and plasma VPA by Ultraviolet-Visible (UV-vis) spectrophotometric immunoassay. The patients presented adequate CLZ levels in relation to the dose. However, NCLZ levels were excessively low and the CLZ/NCLZ ratio very high. Patients with UGT2B10 GT (rs61750900) genotype showed lower NCLZ plasma levels and C/D NCLZ, and higher CLZ/NCLZ ratio versus patients with UGT2B10 GG genotype. VPA, smoking, the presence of UGT2B10 GT genotype and having low albumin levels indicate that the CLZ/NCLZ ratio is affected, mostly coinciding with decreased NCLZ levels and possibly with an increased risk of neutropenia.

Risk factors for clozapine-induced myocarditis and cardiomyopathy: A systematic review and meta-analysis

OBJECTIVE

Clozapine is the most effective medication for treatment-refractory schizophrenia, but it is associated with severe cardiac adverse events including myocarditis and cardiomyopathy. To aid treatment decision-making for clinicians, patients and their carers, we conducted a systematic review and meta-analysis to identify potential risk factors for clozapine-induced myocarditis and cardiomyopathy.

METHODS

A systematic search was conducted of PubMed, Embase, CINAHL, Web of Science, Cochrane and PsycInfo for studies reporting myocarditis and cardiomyopathy among people on clozapine and potential risk factors. We calculated pooled effect sizes on risk factors using a random-effects meta-analytic model. Risk of publication bias was assessed using the Newcastle-Ottawa scale.

RESULTS

Seven studies met the inclusion criteria, of which six studies had quantitative data included in the meta-analysis. The odds of clozapine-induced myocarditis increased with concurrent sodium valproate use (k = 6, n = 903, pooled OR 3.58, 95% CI 1.81-7.06), but were not significantly greater with the use of quetiapine, lithium or selective serotonin reuptake inhibitors. Our qualitative review identified conflicting results reported for increasing age and higher clozapine dose as risk factors for myocarditis. No other factors, including genetic risk, sex, ethnicity, smoking, alcohol, substance abuse or cardiometabolic disease, were associated with greater odds of myocarditis. No risk factors for cardiomyopathy were identified in the literature.

CONCLUSION

Concurrent use of sodium valproate increases the odds of clozapine-induced myocarditis. Thus, clinicians should consider the temporary cessation of sodium valproate during the initial titration phase of clozapine.

Factors predicting serum clozapine levels in Middle Eastern patients: an observational study

BACKGROUND

Despite its superiority over other drugs for psychosis, clozapine remains underused and is associated with many clinical challenges, including difficulties in predicting therapeutic serum levels (350-600 ng/mL). We found no large or recent study that investigated the determinants of serum clozapine levels in Middle Eastern patients. Therefore, we investigated the association between clozapine dose and serum level, and the clinical predictors of the clozapine serum level, in Middle Eastern patients.

METHODS

This cross-sectional study included 94 patients of Middle Eastern ethnicity who attended the Clozapine Clinic in King Saud University Medical City in Riyadh, Saudi Arabia. We used a single measure of the serum clozapine level, which was collected 12 h after the last oral dose of clozapine under steady-state conditions.

RESULTS

The average clozapine dose and serum level were 400 mg/daily and 705 ng/mL, respectively. The majority of patients (59.8%) had serum levels higher than 600 ng/mL. Clozapine dose and serum level were positively correlated (r_s [94] = 0.32, p = 0.002). We generated a predictive model of the serum clozapine level, which revealed that the daily dose, smoking status, use of fluvoxamine or lamotrigine, and body mass index (BMI) predicted 43.6% of the variance in the serum level (p < 0.001). Using this model, we calculated that patients with a BMI of 25 kg/m² would require a clozapine dose between 50 to 275 mg/daily if they were non-smokers, and a dose of 200 to 450 mg/daily if they were smokers, in order to reach a serum clozapine level between 350 to 600 ng/mL. Patients with higher BMI and those receiving fluvoxamine would require lower doses.

CONCLUSIONS

This was a naturalistic study of the clozapine dose-level relationship and the clinical predictors of the serum clozapine level in a sample of Middle Eastern patients. The ratios of clozapine level to dose in our patients more closely resembled those reported in Asian samples than in European samples. These findings do not reduce the value of individualised therapeutic drug monitoring, but may assist clinicians when prescribing clozapine to Middle Eastern patients. Further psychopharmacological studies are needed on this demographic population.

Exploring the usefulness of plasma level determination and pharmacogenetics for patients treated with clozapine

Aims: The aims of the present study were to assess the variance of plasma clozapine (CLZ) levels and to identify the influence of sociodemographic and pharmacogenetic factors on it and to introduce these tools in a clinical setting. Patients & methods: CLZ concentration was measured and genetic variants of CLZ pharmacokinetic and pharmacodynamic factors were assessed in 23 patients with psychotic disorders. Results: A significant association between mean concentration/dose ratio (C/D) and smoking status, age and weight were found. There was a significant difference in mean plasma CLZ levels and gender. The rs762551 AA genotype in smokers had a significantly lower C/D. Conclusion: In addition to classical factors, monitoring of plasma concentrations together with pharmacogenetics led to greater individualization of treatment.

Toxic clozapine level as first indication of severe, acute infection

Background

Clozapine levels can be influenced by many factors, including pharmacogenomic variability, pharmacokinetic drug interactions, and infection/inflammation. The concentration-to-dose ratio (C/D), a measure of a medication's rate of metabolism and clearance, may increase during an acute infection due to decreased medication metabolism and clearance.

Case Report

A 56-year-old White man was restarted on clozapine and titrated up to 350 mg/d with therapeutic steady-state levels (C/D 1.11) on hospital day (HD) 69. At this time, he was also being treated for COPD exacerbation. For the next month, he continued to complain of cough, but vital signs and chest x-ray remained normal. Labs were unremarkable except for occasional leukocytosis that would resolve on repeat evaluation. A routine clozapine level drawn on HD 104, resulted on day 108 and showed clozapine toxicity with C/D 4.05, although the patient was asymptomatic. After receipt of labs on day 109, showing elevated WBC count, he was immediately sent to the emergency room where he was admitted for treatment of pneumonia. On return to the state hospital, the patient was continued on 100 mg clozapine and titrated to 200 mg/d based on low drug levels. He continued to do well on 200 mg/d clozapine with C/D averaging 1.13 (range, 0.75-1.52).

Discussion

Acute infection and illness can lead to significantly increased clozapine levels and toxicity, even if symptoms of toxicity are minimal or absent. This appears to be the first report of a toxic level being the first indication of severe medical illness.

Reasons for admission to a general medical hospital for patients taking clozapine

BACKGROUND

Clozapine is associated with a diverse range of side effects. In addition, patients prescribed clozapine commonly suffer with medical comorbidities.

OBJECTIVES

This study aimed to characterise patients prescribed clozapine who required medical admission, understand reasons for admission, identify areas for interventions to prevent future admission and describe clozapine management during the inpatient stay.

DESIGN

We conducted a retrospective analysis of patients prescribed clozapine who were admitted to a general medical hospital in a 12-month period.

METHOD

Data were collected using electronic drug charts and notes.

RESULTS

In total, 114 clozapine patients were hospitalised. Twenty-eight patients (25%) were admitted because of infection, 12 (11%) were elective admissions and 12 (11%) had gastrointestinal problems. Most patients admitted were Black (54%) and half were female. Few changes were made to clozapine dosing on admission or during the inpatient stay. Most patients had been taking clozapine for many years at the point of admission, the majority were able to continue taking it for the duration of their medical treatment and were discharged on the same dose they were taking prior to admission. Clozapine plasma concentrations were not consistently measured with only 18 (16%) patients having one or more plasma concentrations determined during their admission. The median clozapine plasma concentration on admission was 0.48 mg/L (nor-clozapine 0.21 mg/L), with a range of 0.09 to 3.9 mg/L. Three patients were admitted to the intensive care unit during their admission; all were discharged on clozapine. Four patients died; one from lung adenocarcinoma, one bowel obstruction, one cardiac arrest and one chest sepsis. In total, 27 patients (23%) had their clozapine stopped on admission, 6 (22% of this group) unintentionally.

CONCLUSIONS

Our study found that the most common reason for admission for patients taking clozapine was infection. Plasma concentrations were not measured routinely despite clozapine having a narrow therapeutic index and enhanced potential for toxicity in the medically unwell patient.

Clozapine blood level assessment using a point-of-care device: feasibility and reliability

BACKGROUND

Therapeutic drug monitoring (TDM) is useful to assess clozapine adherence and optimize treatment. However, analysis of venous blood levels by liquid chromatography tandem mass spectrometry (LC-MS/MS) is often logistically complicated and process time is prolonged.

OBJECTIVE

To assess the feasibility and reliability of a new point-of-care device, (MyCare™ Insite), using capillary blood for clozapine therapeutic monitoring.

METHODS

Matched venous and capillary blood samples were collected from patients treated with clozapine on a stable dose. Samples were analyzed by LC-MS/MS and MyCare Insite Clozapine Test. Clozapine plasma levels were compared between methods using linear regression model. Both patients and treatment team completed questionnaires about the feasibility of blood sampling.

RESULTS

Of the total sample (44 patients, 61% males, mean age 43 ± 12 years), mean daily clozapine dose was 293 ± 134 mg/day. Linear regression model demonstrated high correlation with R ² = 0.83 (p < 0.0001) and mean difference of 26 ± 162 ng/ml. More than 60% of the patients found the clozapine TDM to be important. Most of the participants (58%) favored the capillary sampling and 11% claimed that testing method would affect their adherence to TDM. Moreover, a larger portion (72%) strongly preferred to be tested at the office rather than at the lab.

CONCLUSIONS

The point-of-care device offers an accessible and satisfactory measurement of clozapine blood levels. Both patients and healthcare providers reported preference for capillary sampling as well as for the in-office TDM procedure. The immediate results provided by the device can facilitate rapid and informed clinical decisions and therefore improve clozapine treatment outcomes.

Combining Therapeutic Drug Monitoring and Pharmacokinetic Modelling Deconvolutes Physiological and Environmental Sources of Variability in Clozapine Exposure

Background: Clozapine is a key antipsychotic drug for treatment-resistant schizophrenia but exhibits highly variable pharmacokinetics and a propensity for serious adverse effects. Currently, these challenges are addressed using therapeutic drug monitoring (TDM). This study primarily sought to (i) verify the importance of covariates identified in a prior clozapine population pharmacokinetic (popPK) model in the absence of environmental covariates using physiologically based pharmacokinetic (PBPK) modelling, and then to (ii) evaluate the performance of the popPK model as an adjunct or alternative to TDM-guided dosing in an active TDM population. Methods: A popPK model incorporating age, metabolic activity, sex, smoking status and weight was applied to predict clozapine trough concentrations (C_min) in a PBPK-simulated population and an active TDM population comprising 142 patients dosed to steady state at Flinders Medical Centre in Adelaide, South Australia. Post hoc analyses were performed to deconvolute the impact of physiological and environmental covariates in the TDM population. Results: Analysis of PBPK simulations confirmed age, cytochrome P450 1A2 activity, sex and weight as physiological covariates associated with variability in clozapine C_min (R² = 0.7698; p = 0.0002). Prediction of clozapine C_min using a popPK model based on these covariates accounted for <5% of inter-individual variability in the TDM population. Post hoc analyses confirmed that environmental covariates accounted for a greater proportion of the variability in clozapine C_min in the TDM population. Conclusions: Variability in clozapine exposure was primarily driven by environmental covariates in an active TDM population. Pharmacokinetic modelling can be used as an adjunct to TDM to deconvolute sources of variability in clozapine exposure.

Clozapine metabolism may be affected by Gilbert's syndrome: case report and discussion

A 34-year-old man with treatment-resistant schizophrenia and Gilbert's syndrome was treated with clozapine and found to have unusually slow and fluctuating metabolism of clozapine, resulting in difficulty achieving a well-tolerated and stable plasma clozapine level. Gilbert's syndrome is a relatively common (3-10% prevalence) genetic condition which results in altered hepatic metabolism. This case report demonstrates in vivo the finding of previous in-vitro research suggesting that the UGT1A1 7/7 mutation most commonly associated with Gilbert's syndrome may result in decreased clozapine excretion. Given evidence of an increased prevalence of Gilbert's syndrome in patients with schizophrenia, further investigation into this possible correlation may improve understanding and prediction of clozapine dosage.

Metabolic Effects of Clozapine Administration Based on Sex Differences and the Relationships Between Dosage and Prolactin Levels: An Observational Study

OBJECTIVE

Clozapine is the second-generation antipsychotic that induces the largest metabolic disorders. However, evidence is limited to the liabilities based on sex differences. This study aimed to investigate the effects of clozapine treatment on metabolic and neuroendocrine parameters, and the relationships between prescribed clozapine dosage and prolactin levels that may be associated with plasma clozapine concentrations, in 24 female and 24 male Japanese schizophrenia inpatients switched to clozapine.

METHODS

Within female and male subjects, sequential changes in 7 items of metabolic parameters, including anthropometric measurements, fasting serum lipid components and glucose levels, and estimated insulin resistance at 2 months were evaluated and analyzed against clozapine dosages and prolactin levels at 2 months.

RESULTS

Triglyceride levels, triglyceride to high-density lipoprotein ratios reflecting insulin resistance and glucose levels increased in female and male subjects. High-density lipoprotein cholesterol levels decreased in female and male subjects. High-density lipoprotein cholesterol levels were negatively correlated with prolactin levels in female subjects, and glucose levels were positively correlated with prolactin levels in male subjects, although clozapine doses showed no such correlations.

CONCLUSIONS

Clozapine administration developed sex-neutral metabolic disorders in the study subjects. Higher prolactin levels seemed to increase the risk of dyslipidemia and hyperglycemia with sex differences, which suggested that serum prolactin levels other than clozapine doses might be useful to predict sex-specific metabolic disorders. Further prospective studies, combining measurement of metabolic hormones and plasma concentrations of clozapine and its metabolites, will help to confirm our findings.

Rapid Simultaneous Determination of 14 Antidepressants and 13 Antipsychotics in Human Plasma by Using High-Performance Liquid Chromatography-Tandem Mass Spectrometry With Dynamic Multiple Reaction Monitoring and Its Application to Therapeutic Drug Monitoring

BACKGROUND

A comprehensive, stable, and efficient high-performance liquid chromatography-tandem mass spectrometry method was developed for rapidly analyzing 14 antidepressants and 13 antipsychotics in human plasma for routine clinical therapeutic drug monitoring.

METHODS

Simple protein precipitation was used for the pretreatment of plasma samples; dynamic multiple reaction monitoring was used to avoid the loss of sensitivity caused by numerous ion transitions. In all, 80 ion transitions of 40 compounds were quantitatively determined in 6 minutes.

RESULTS

The limit of detection for the 27 analytes was in the range of 0.1-30 ng/mL, and all calibration lines prepared using blank plasma were linear with a correlation coefficient of r2 ≥ 0.99. The method was accurate and precise with acceptable intraday and interday precisions (coefficients of variation, ≤20% for a lower limit of quantification and ≤15% for other quality control samples) and an accuracy of 85.51%-114.77%. This analysis method has been completely validated and successfully used in routine clinical therapeutic drug monitoring for more than 9963 samples [including 488 samples having drug concentrations above the laboratory alert level (supra-alert-level samples)] at Xiamen Xianyue Hospital.

CONCLUSIONS

This dynamic method is comprehensive (includes most antidepressants and antipsychotics listed in China), reliable (stably used for almost 2 years), and efficient (convenient sample processing and short run time) and provides a large amount of meaningful data for optimized pharmacotherapy. Our experimental data from the plasma concentrations of supra-alert-level samples could serve as a reference for the interpretation of the pharmacokinetics of patients with a high risk of toxicity or loss of tolerability.

Clozapine and Norclozapine Plasma Levels in Patients Switched Between Different Liquid Formulations

BACKGROUND AND OBJECTIVE

Clozapine is the drug of choice for treatment-resistant schizophrenia. The primary objective of this study was to compare plasma clozapine and N-desmethylclozapine levels in patients switched between 2 liquid formulations [Denzapine suspension and clozapine oral solution (St George's ZTAS)]. Secondary objectives included comparison of safety, tolerability, and patient acceptability.

METHODS

This was a noninterventional, observational, prospective follow-up of patients consecutively switched between formulations of clozapine liquid in a large inner-city NHS mental health trust. The authors also performed retrospective analysis of outcomes from patient case notes.

RESULTS

The authors identified 43 patients receiving Denzapine suspension in the trust. Data were available for 43 patients switched from Denzapine to clozapine oral solution (St George's ZTAS), among whom, 15 (32%) were excluded from the analysis. Of the 28 patients for whom data were available, the 90% confidence interval for the ratio of mean values for corrected Cmin 91.5 (85.2%-98.4%) and uncorrected Cmin 91.2 (84.4%-98.6%) were within the guideline range of bioequivalence (80%-125%). Safety and tolerability profiles were comparable between the 2 formulations (P = 0.10). Patient acceptability was also similar between the brands in most domains. However, there was a taste preference for Denzapine suspension.

CONCLUSIONS

No significant difference in clozapine plasma levels was observed after switching from Denzapine suspension to a recently introduced clozapine solution. This study also highlights the significance of medicinal characteristics such as taste for patient acceptability and compliance.

High-Dose Fluvoxamine Augmentation to Clozapine in Treatment-Resistant Psychosis

BACKGROUND

Although clozapine is the gold standard for treatment-resistant schizophrenia, more than 30% of patients remain unresponsive to clozapine monotherapy and may benefit from augmentation strategies. Fluvoxamine augmentation of clozapine may be beneficial in treatment resistance because of pharmacokinetic interactions, allowing for lower clozapine dosages with higher clozapine serum levels and an increased clozapine-to-norclozapine ratio, which can modify adverse effects. An augmentation strategy using higher fluvoxamine doses may also improve persistent negative, anxiety, and obsessive-compulsive symptoms through fluvoxamine's serotonergic activity.

METHODS

Through chart review, we identified 4 cases of patients with treatment-resistant psychosis who underwent high-dose fluvoxamine augmentation of clozapine to target residual negative symptoms, refractory psychosis, anxiety, and obsessive-compulsive symptoms.

FINDINGS

This augmentation strategy continued in 2 patients after discharge who showed clinical improvement without significant adverse effects. Two patients experienced adverse effects that led to the fluvoxamine discontinuation. Despite the fact that fluvoxamine augmentation led to symptom improvement in only 2 patients, all patients achieved high serum clozapine levels. Hematologic parameters were monitored in all patients, and no abnormalities were observed. No severe adverse effects of clozapine were experienced.

CONCLUSIONS

Although high variability of responses and adverse effects were observed during fluvoxamine augmentation to clozapine, this strategy was successful in increasing clozapine serum levels. Through fluvoxamine's serotonergic effects, this strategy may confer benefit to residual negative, obsessive, and anxiety symptoms. Limitations of this case series include the retrospective nature, absence of controls, diversity of diagnoses, multiple interventions in each patient, and lack of masked raters.

Point-of-care measurement of clozapine concentration using a finger-stick blood sample

BACKGROUND

The use of clozapine demands regular monitoring of clozapine plasma concentrations and of white blood cell parameters. The delay between sending blood samples for analysis and receiving the results hinders clinical care. Point-of-care testing (POCT) can provide drug assay results within a few minutes.

AIM

This study aimed to investigate the utility of a novel point-of-care device that can measure clozapine concentrations using capillary blood samples collected via a finger stick.

METHOD

During a five-week period starting in June 2019 eligible patients were asked to provide a finger-stick capillary sample in addition to their usual venous blood sample. Samples were analysed by the novel point-of-care device and by the standard laboratory method. Capillary blood samples were tested by the MyCare™ Insite POCT analyser, and a quantitative measurement of clozapine concentration was provided within six minutes.

RESULTS

A total of 309 patients agreed to measurements by the two methods. Analysis revealed clozapine concentrations in venous blood as determined by the laboratory method ranged from 20 to 1310 ng/mL and by POCT from 7 to 1425 ng/mL. There was a strong positive correlation (R = 0.89) between the results from the venous and the capillary sample methods. The slope of the association between standard assay and MyCare™ Insite was 1.0 with an intercept of -21 ng/mL, indicating minimal bias.

CONCLUSION

Clozapine concentrations can be accurately measured at the point of care using capillary blood samples collected via a finger stick. This approach may be more acceptable than venous sampling to patients and, with almost instant results available, more useful to clinicians.

Integrative Genomic-Epigenomic Analysis of Clozapine-Treated Patients with Refractory Psychosis

Clozapine (CLZ) is the only antipsychotic drug that has been proven to be effective in patients with refractory psychosis, but it has also been proposed as an effective mood stabilizer; however, the complex mechanisms of action of CLZ are not yet fully known. To find predictors of CLZ-associated phenotypes (i.e., the metabolic ratio, dosage, and response), we explore the genomic and epigenomic characteristics of 44 patients with refractory psychosis who receive CLZ treatment based on the integration of polygenic risk score (PRS) analyses in simultaneous methylome profiles. Surprisingly, the PRS for bipolar disorder (BD-PRS) was associated with the CLZ metabolic ratio (pseudo-R2 = 0.2080, adjusted p-value = 0.0189). To better explain our findings in a biological context, we assess the protein-protein interactions between gene products with high impact variants in the top enriched pathways and those exhibiting differentially methylated sites. The GABAergic synapse pathway was found to be enriched in BD-PRS and was associated with the CLZ metabolic ratio. Such interplay supports the use of CLZ as a mood stabilizer and not just as an antipsychotic. Future studies with larger sample sizes should be pursued to confirm the findings of this study.

Clinical risk factors, phenomenology and the impact of clozapine induced obsessive compulsive symptoms

The aim of this study was to investigate the clinical risk factors, phenomenology and the impact of clozapine induced obsessive-compulsive symptoms (OCS) in patients with schizophrenia. One hundred twenty-two patients receiving clozapine treatment for at least 6 weeks were assessed with Structured Clinical Interview for Axis-I Disorders for DSM-IV, Positive and Negative Syndrome Scale, Yale-Brown Obsessive Compulsive Scale and Checklist, Calgary Depression Scale, Clinical Global Impression Scale and WHO-Disability Assessment Schedule-II. Information about past and current clinical status were gathered through clinical interviews and medical records. With clozapine 44.3% of the patients had de novo OCS, 33.6% had OCS both before and after clozapine, 21.3% didn't report any OCS. Clozapine doses, clozapine and norclozapine plasma levels were not significantly different. Severity of OCS was affected by clozapine and norclozapine plasma levels, and correlated with increased disability. Obsessions were less in clozapine induced OCS group, and compulsions, especially of checking subtypes, were predominant, compared to the group with prior history of OCS, who reported a significant increase in checking compulsion after clozapine treatment. Clozapine induced OCS should be considered during cost/benefit assessment of clozapine treatment, and understanding the risk factors and its different phenomenology may shed light into the underlying mechanisms.

Associations between plasma clozapine/N-desmethylclozapine ratio, insulin resistance and cognitive performance in patients with co-morbid obesity and ultra-treatment resistant schizophrenia

Clozapine (CLZ), the sole antipsychotic with superior efficacy for ultra-treatment resistant schizophrenia (TRS), is limited by adverse effects, including metabolic dysregulation. Clozapine's main metabolite, N-desmethylclozapine (NDMC), has potent 5-HT2C antagonist properties which may explain this metabolic dysfunction, thus the CLZ:NDMC ratio is of particular interest. High insulin resistance states could be associated with CYP1A2 induction and lower CLZ:NDMC ratios. Additionally, lower CLZ:NDMC ratios have been associated with better cognitive, but worse metabolic functioning. This study investigated associations between metabolic and cognitive parameters with the CLZ/NDMC ratio. Primary outcomes included relationships between the CLZ:NDMC ratio to the homeostatic model assessment for insulin resistance (HOMA-IR) and Brief Assessment of Cognition in Schizophrenia (BACS) composite z-scores. Secondary outcomes assessed relationships between CLZ:NDMC ratios to fasting insulin, BMI, weight, fasting glucose, and BACS digit sequencing z-scores. 38 patients who were overweight or obese with schizophrenia or schizoaffective disorder completed fasting bloodwork, anthropometric, psychopathological, and cognitive assessments. Multivariate regressions found a statistically significant inverse association between the CLZ/NDMC ratio and HOMA-IR (B = - 1.028, SE B = .473, β = - 0.348 p = 0.037), which may have been driven by fasting insulin levels (B = - 27.124, SE B = 12.081, β = - 0.351 p = 0.031). The CLZ/NDMC ratio may predict insulin resistance/metabolic comorbidity among patients with TRS receiving clozapine.

Outcomes in treatment-resistant schizophrenia: symptoms, function and clozapine plasma concentrations

BACKGROUND

Clozapine is the only medication licenced for treating patients with treatment-refractory schizophrenia. However, there are no evidence-based guidelines as to the optimal plasma level of clozapine to aim for, and their association with clinical and functional outcome.

OBJECTIVE

We assessed the relationship between clinical and functional outcome measures and blood concentrations of clozapine among patients with treatment-refractory psychosis.

METHODS

Data were reviewed in 82 patients with treatment-refractory psychosis admitted to a specialised tertiary-level service and treated with clozapine. Analysis focussed on the relationship between clozapine and norclozapine plasma concentrations and the patient's clinical symptoms and functional status.

RESULTS

Clinical symptom improvement was positively correlated with norclozapine plasma concentrations and inversely correlated with clozapine to norclozapine plasma concentrations ratio. Clozapine concentrations showed a bimodal association with clinical improvement (peaks around 350 and 660 ng/ml). Clinical symptom improvement correlated with functional outcomes, although there was no significant correlation between the latter and clozapine or norclozapine plasma concentrations.

CONCLUSION

Clozapine treatment was associated with optimal clinical improvement at two different peak plasma concentrations around 350 and 650 ng/ml. Clinical improvement was associated with functional outcome; however, functionality was not directly associated with clozapine concentrations. A subset of patients may require higher clozapine plasma concentrations to achieve clinical improvement.

Comprehensive assessment of exposure to clozapine in association with side effects among patients with treatment-resistant schizophrenia: a population pharmacokinetic study

BACKGROUND

There have been scarce data on the distribution of clozapine concentrations in comparison with the recommended range (350-600 ng/ml) or their relationship with side effects among patients with treatment-resistant schizophrenia. Furthermore, no studies have assessed the association between side effects and overall exposure to the drug by calculating the 24-h area-under-curve (AUC).

METHODS

In- and outpatients with schizophrenia or schizoaffective disorder (ICD-10) who were receiving a stable dose of clozapine for ⩾2 weeks were included. Side effects were assessed using the Glasgow antipsychotic side-effects scale for clozapine (GASS-C). Using two collected plasma samples, plasma clozapine and norclozapine concentrations at peak and trough and their 24-h AUC were estimated using population pharmacokinetic models.

RESULTS

A total of 108 patients completed the study (mean ± SD age, 43.0 ± 10.1 years; clozapine dose, 357.5 ± 136.9 mg/day); 33 patients (30.6%) showed estimated trough concentrations of clozapine within the recommended range (350-600 ng/ml) whereas the concentrations were higher and lower than this range among 37 (43.5%) and 28 (25.9%) patients (%), respectively. There were no significant correlations between estimated peak or trough concentrations or 24-h AUC of both clozapine or norclozapine, and GASS-C total or individual scores. No significant differences were found between GASS-C total or individual item scores between the patients with estimated trough concentrations of clozapine of >600 ng/ml and the other subjects.

CONCLUSION

The results suggest that clozapine or norclozapine concentrations are not linked directly to the extent of side effects experienced in clozapine-treated patients with treatment-resistant schizophrenia while the cross-sectional study design limits the interpretation of any causal relationships. These findings indicate that side effects associated with clozapine may occur at any dose or concentration.

Anticholinergic Burden and Cognitive Performance in Patients With Schizophrenia: A Systematic Literature Review

Objective: Cognitive impairment in schizophrenia forms the key cause of the disease's disability, leading to serious functional, and socioeconomic implications. Dopaminergic-cholinergic balance is considered essential to cognitive performance in schizophrenia and patients are often treated with many drugs with anticholinergic properties. This study aims to examine the cognitive impact of anticholinergic burden in patients with schizophrenia. Methods: A systematic literature review was performed on English-language studies published on PubMed, Embase, and Web of Science, from inception to June 2021, to identify research studies that examined the effect of anticholinergic load on cognition in clinically stable patients with schizophrenia. No restrictions on study design, age of participants, or geographical distribution were applied. Two researchers performed independently the screening and shortlisting of the eligible articles. A narrative synthesis of the main characteristics and findings of studies included was reported. Results: In total, 17 articles of varying methodological design met the inclusion criteria. Three of them found statistically significant improvement in cognition after anticholinergic tapering without adverse effects. Thirteen studies found a statistically significant association between high anticholinergic burden and cognitive impairment (neurocognitive composite scores and individual cognitive domains such as learning and memory, executive function, processing speed), apart from a study, related to the specific characteristics of clozapine. Conclusions: Medication with increased anticholinergic load has been found in most of the studies to negatively affect neurocognitive performance of patients with schizophrenia. However, the clinical and methodological heterogeneity of studies included limit our interpretation and conclusions.

Alcohol intake potentiates clozapine adverse effects associated to CYP1A2*1C in patients with refractory psychosis

Clozapine (CLZ) is an atypical antipsychotic and the gold standard for refractory psychosis treatment. However, there is little information regarding pharmacogenetics of CLZ in patients with refractory psychosis and its clinical correlation with alcohol intake. Although neurological effects of CLZ in patients with concomitant alcohol intake are documented, its use is very common in patients with psychosis. We explored the impact of CYP1A2, CYP2D6, CYP2C19, and CYP3A4 genetic variants on CLZ pharmacokinetics and side effects, along with coffee/alcohol/tobacco consumption habits and clinical data of 48 adult patients with refractory psychosis on CLZ antipsychotic monotherapy. Relevant CYP variants in CLZ metabolism were evaluated by targeted genotyping and multiplex ligation-dependent probe amplification. CLZ and its main metabolite plasma concentrations were determined by high performance liquid chromatography. Biochemical and molecular data, along with other potential confounders, were included in the analysis by linear regression. Overall, CYP variants showed no effect on CLZ pharmacokinetics. The rs2069514 variant in homozygous genotype (also known as CYP1A2*1C/*1C) was associated with CLZ adverse reactions in Mexican patients with refractory psychosis (OR = 3.55 CI₉₅  = 1.041-12.269, p = .043) and demonstrated that this effect is doubled by concomitant alcohol consumption (OR = 7.9 CI₉₅  = 1.473-42.369, p = .016). Clinicians should be aware of this information before starting CLZ use, when treating patients with refractory psychosis, who are alcohol drinkers and carriers of this genetic variant in order to prevent CLZ-related adverse reactions. Nevertheless, our findings should be replicated in larger samples.

Relationship of Change in Plasma Clozapine/N-desmethylclozapine Ratio with Cognitive Performance in Patients with Schizophrenia

OBJECTIVE

The clozapine/N-desmethylclozapine (NDMC) ratio is proposed to be used as a predictor of cognitive performance in clozapine-treated patients, as its principal metabolite, NDMC, has an opposite action with clozapine on the cholinergic system. The aim of this study is to determine whether clozapine has influence on cognitive performance in accordance with changes in the clozapine/NDMC in patients with schizophrenia.

METHODS

The data of fifteen patients with schizophrenia, who had initial and follow-up assessments after starting clozapine treatment, were retrospectively collected. The assessments included clinical scale, cognitive battery, and pharmacological data including plasma concentrations of clozapine and NDMC. The data were analyzed with Pearson correlation and stepwise multiple regression analyses.

RESULTS

ΔAttention/vigilance, Δsocial cognition, and Δcomposite score had a significant correlation with Δclozapine/NDMC ratio, while ΔWorking memory had correlation with Δclozapine concentration and ΔNDMC concentration, and Δsocial cognition had association with Δclozapine concentration. Multiple regression analysis showed that Δattention/vigilance had negative association with Δclozapine/NDMC ratio, Δworking memory had negative relation with Δclozapine concentration, and that Δsocial cognition had negative association with Δclozapine concentration.

CONCLUSION

This finding implicates that lowering the clozapine/NDMC ratio could enhance cognition in patients with schizophrenia treated with clozapine.

Clozapine in the treatment of refractory schizophrenia: a practical guide for healthcare professionals

BACKGROUND

Clozapine remains the only medication licensed for treating refractory schizophrenia. However, it remains underutilized in part due to concerns regarding adverse events.

SOURCES OF DATA

Published literature.

AREAS OF AGREEMENT

Common adverse events during clozapine treatment include sedation, hypersalivation, postural hypotension, dysphagia, gastrointestinal hypomotility, weight gain, diabetes mellitus and dyslipidaemia. Rare but serious events include agranulocytosis, cardiomyopathy, myocarditis, pneumonia, paralytic ileus and seizure.

AREAS OF CONTROVERSY

It remains unclear how best to minimize clozapine-induced morbidity/mortality (i) during dose titration, (ii) from hypersalivation and (iii) from gastrointestinal hypomotility. It is also unclear how clozapine pharmacokinetics are affected by (i) gastrointestinal hypomotility, (ii) systemic infection and (iii) passive exposure to cigarette smoke. Whether monthly haematological monitoring needs to continue after 12 months of uninterrupted therapy is also a subject of debate.

GROWING POINTS

There is a need for better management of serious clozapine-related adverse events in addition to agranulocytosis. There is also a need for better education of patients and carers, general practitioners, A&E and ITU staff and others of the problems posed in using clozapine safely.

AREAS TIMELY FOR DEVELOPING RESEARCH

There is a need for more research on assessing clozapine dosage (i) as patients get older, (ii) with respect to exposure to cigarette smoke and (iii) optimizing response if adverse events or other factors limit dosage.

[Informations on psychotropics and their adaptations for patients suffering from mental disorders in France during the SARS-CoV-2 epidemic]

The 2019-20 coronavirus pandemic (SARS-CoV-2; severe acute respiratory syndrome coronavirus 2) has dramatic consequences on populations in terms of morbidity and mortality and in social terms, the general confinement of almost half of the world's population being a situation unprecedented in history, which is difficult today to measure the impact at the individual and collective levels. More specifically, it affects people with various risk factors, which are more frequent in patients suffering from psychiatric disorders. Psychiatrists need to know: (i) how to identify, the risks associated with the prescription of psychotropic drugs and which can prove to be counterproductive in their association with COVID-19 (coronavirus disease 2019), (ii) how to assess in terms of benefit/risk ratio, the implication of any hasty and brutal modification on psychotropic drugs that can induce confusion for a differential diagnosis with the evolution of COVID-19. We carried out a review of the literature aimed at assessing the specific benefit/risk ratio of psychotropic treatments in patients suffering from COVID-19. Clinically, symptoms suggestive of COVID-19 (fever, cough, dyspnea, digestive signs) can be caused by various psychotropic drugs and require vigilance to avoid false negatives and false positives. In infected patients, psychotropic drugs should be used with caution, especially in the elderly, considering the pulmonary risk. Lithium and Clozapine, which are the reference drugs in bipolar disorder and resistant schizophrenia, warrant specific attention. For these two treatments the possibility of a reduction in the dosage - in case of minimal infectious signs and in a situation, which does not allow rapid control - should ideally be considered taking into account the clinical response (even biological; plasma concentrations) observed in the face of previous dose reductions. Tobacco is well identified for its effects as an inducer of CYP1A2 enzyme. In a COVID+ patient, the consequences of an abrupt cessation of smoking, particularly related with the appearance of respiratory symptoms (cough, dyspnea), must therefore be anticipated for patients receiving psychotropics metabolized by CYP1A2. Plasma concentrations of these drugs are expected to decrease and can be related to an increase risk of relapse. The symptomatic treatments used in COVID-19 have frequent interactions with the most used psychotropics. If there is no curative treatment for infection to SARS-CoV-2, the interactions of the various molecules currently tested with several classes of psychotropic drugs (antidepressants, antipsychotics) are important to consider because of the risk of changes in cardiac conduction. Specific knowledge on COVID-19 remains poor today, but we must recommend rigor in this context in the use of psychotropic drugs, to avoid adding, in patients suffering from psychiatric disorders, potentially vulnerable in the epidemic context, an iatrogenic risk or loss of efficiency.

A Rational Use of Clozapine Based on Adverse Drug Reactions, Pharmacokinetics, and Clinical Pharmacopsychology

Using Richardson and Davidson's model and the sciences of pharmacokinetics and clinical pharmacopsychology, this article reviewed the: (1) poor life expectancy associated with treatment-resistant schizophrenia (TRS), which may be improved in patients who adhere to clozapine; (2) findings that clozapine is the best treatment for TRS (according to efficacy, effectiveness and well-being); and (3) potential for clozapine to cause vulnerabilities, including potentially lethal adverse drug reactions such as agranulocytosis, pneumonia, and myocarditis. Rational use requires: (1) modification of the clozapine package insert worldwide to include lower doses for Asians and to avoid the lethality associated with pneumonia, (2) the use of clozapine levels for personalizing dosing, and (3) the use of slow and personalized titration. This may make clozapine as safe as possible and contribute to increased life expectancy and well-being. In the absence of data on COVID-19 in clozapine patients, clozapine possibly impairs immunological mechanisms and may increase pneumonia risk in infected patients. Psychiatrists should call their clozapine patients and families and explain to them that if the patient develops fever or flu-like symptoms, the psychiatrist should be called and should consider halving the clozapine dose. If the patient is hospitalized with pneumonia, the treating physician needs to assess for symptoms of clozapine intoxication since halving the dose may not be enough for all patients; consider decreasing it to one-third or even stopping it. Once the signs of inflammation and fever have disappeared, the clozapine dose can be slowly increased to the prior dosage level.