A systematic review and meta-analysis of the effect of clozapine on cognitive functions in patients with treatment-resistant schizophrenia

Letter to the FDA Proposing Major Changes in the US Clozapine Package Insert Supported by Clozapine Experts Worldwide. Part I: A Review of the Pharmacokinetic Literature and Proposed Changes

PURPOSE/BACKGROUND

Clozapine was approved in the United States (US) using 1989 regulations and knowledge. After 30 years, many sections of the US package insert (PI) are outdated.

METHODS

We comprehensively reviewed the literature to propose PI updates. We present the information in 2 articles. In Part I, we focus on basic pharmacology based on 407 relevant articles. Part II focuses on clinical aspects and pharmacovigilance.

FINDINGS/RESULTS

Based on more recent expectations of Food and Drug Administration regulations, we reviewed clozapine basic pharmacology including the following: 1) clearance, 2) pharmacokinetics and pharmacodynamics, and 3) monitoring tools. We identified 9 major problems in the basic pharmacological sections of the PI including the following: 1) in vivo studies indicate that clozapine is dependent on CYP1A2 for its metabolism, 2) the minor role of CYP2D6 in clozapine metabolism requires removing the PI recommendation to lower clozapine doses in CYP2D6 poor metabolizers, 3) in nontoxic concentrations CYP3A4 has a minor role in clozapine metabolism and potent CYP3A4 inhibitors lack clinically relevant effects, 4) several drug-drug interactions need to be updated based on recent literature, 5) systemic inflammation may decrease clozapine metabolism and increase the risk of clozapine intoxication, 6) obesity may decrease clozapine metabolism, 7) patients of Asian and Indigenous American ancestry need lower clozapine doses, 8) personalized titration and c-reactive protein monitoring should be considered until prospective studies are available, and 9) the half-life section needs to be modified to acknowledge that single dosing at night is frequent in the US.

IMPLICATIONS/CONCLUSIONS

An improvement in the US clozapine PI may lead to improvement in PIs worldwide.

The relationship of cardiovascular disease risk, clozapine antipsychotic use and cognitive function in a large Chinese schizophrenia cohort

OBJECTIVE

This study explores the intricate relationship between clozapine use, cardiovascular disease (CVD) risk, and cognitive function in patients with schizophrenia (SCZ).

METHODS

A cohort comprising 765 patients was stratified based on clozapine usage. Data on demographics, clinical characteristics, and glycolipid metabolism were collected. The Framingham Risk Score and vascular age were calculated using gender-specific Cox regression calculators. Cognitive function was assessed with the Repeatable Battery for Assessment of Neuropsychological Status.

RESULTS

Among the patients, 34.6 % were clozapine users. Clozapine users exhibited lower systolic blood pressure, high-density lipoprotein cholesterol and total cholesterol (all ps < 0.05). Furthermore, clozapine users exhibited higher PANSS scores, along with lower scores in RBANS scores (all ps < 0.05). Correlation analysis revealed positive correlation between CVD risk in non-clozapine users and negative symptom scores (r = 0.074, p = 0.043), and negative correlation with positive symptom scores and RBANS scores (r = -0.121, p = 0.001; r = -0.091, p = 0.028). Multivariate stepwise regression analysis indicated that attention scores as predictive factors for increased CVD risk in clozapine users (B = -0.08, 95 %CI = -0.11 to -0.03, p = 0.003).

CONCLUSIONS

Patients with SCZ using clozapine exhibit more severe clinical symptoms and cognitive impairments. Attention emerges as a predictor for increased CVD risk in clozapine users.

Clozapine/norclozapine plasma level ratio and cognitive functioning in patients with schizophrenia spectrum disorders: a systematic review

Background

Extant research on cognitive functioning in treatment-resistant schizophrenia (TRS) is limited and of poor quality. Cognitive impairments in patients with schizophrenia spectrum disorders (SSD) significantly influence quality of life. In patients with TRS, clozapine (CLO) is not consistently associated with improved cognitive functioning. The active metabolite n-desmethylclozapine (norclozapine (NCLO)) potentially exerts procognitive effects due to cholinergic and glutamatergic activity. Unfortunately, research on CLO/NCLO ratio and cognitive functioning is even more scarce.

Objectives

To review the literature on the effect of the CLO/NCLO ratio on cognitive functioning in patients with SSD.

Design

This is a systematic review.

Data sources and methods

A search was carried out in the electronic databases Embase, PsycINFO, PubMed, Cochrane and the Cochrane Controlled Register of Trials with no restrictions in language or publication year.

Results

We identified 15 relevant studies (longitudinal, k = 4; cross-sectional, k = 11). The study population consisted of adult clozapine users (n = 953) with varying degrees of treatment resistance. Specific cognitive domains and overall cognitive functioning were assessed using various neuropsychological tests and a composite score, respectively. Eleven studies were considered of fair quality (longitudinal: k = 2, cross-sectional: k = 9). In one longitudinal study, a negative causal relationship was found between the CLO/NCLO ratio and attention/vigilance and a negative correlation between social cognition and the composite score (n = 11). No significant correlations were found between the CLO/NCLO ratio and the cognitive domains processing speed, reasoning/problem solving, or for working memory (k = 1, n = 11), verbal learning (k = 1, n = 43) or visual learning (k = 2, n = 54). Study designs and populations were heterogeneous, and the analysis of confounding factors was limited and inconsistent.

Conclusion

Clinical evidence is too scarce to support the hypothesis of a procognitive effect of NCLO. Personalised CLO treatment by modulating the CLO/NCLO ratio remains a distant prospect. Recommendations for future CLO research and anticipated limitations are discussed.

Trial registration

This systematic review was preregistered with PROSPERO (CRD42023385244).

Factors associated with cognitive dysfunction in treatment-responsive and -resistant schizophrenia: A pilot cross-sectional study

BACKGROUND

Cognitive dysfunction is a core feature of schizophrenia. Although treatment-resistant schizophrenia (TRS) exhibits wide-ranging neuropsychological deficits, factors defining cognitive prognosis in TRS are unclear. We aimed to clarify the association between cognitive dysfunction and factors, such as plasma concentrations of clozapine (CLZ), N-desmethylclozapine (NDMC), and homovanillic acid (HVA), due to differences in antipsychotic responses in patients with schizophrenia.

METHODS

This pilot cross-sectional study included 60 Japanese patients (35 with TRS and 25 with non-CLZ antipsychotic responders (AR)). Cognitive function was evaluated using the Brief Assessment of Cognition Short Form (BAC-SF). Plasma concentrations of HVA, CLZ, and NDMC were analyzed by high-performance liquid chromatography.

RESULTS

The cognitive performance of patients with AR was better than that of patients with TRS in all tasks. No significant cognitive differences were detected between the CLZ responders and non-responders. The severity of negative and extrapyramidal symptoms was found to be potentially negatively associated with BAC-SF composite and several subtest scores. In patients with TRS, chlorpromazine equivalents and the CLZ/NDMC ratio were identified as factors negatively associated with Digit Sequencing and the Symbol Coding subtest scores of the BAC-SF, respectively.

CONCLUSIONS

Our study suggests that patients with TRS experience worse cognitive dysfunction than those with AR, and CLZ responsiveness in TRS may be not associated with cognitive dysfunction. Additionally, higher chlorpromazine equivalents and the CLZ/NDMC ratio may be associated with severity of cognitive dysfunction in patients with TRS. Further studies are required to clarify the relationship between treatment response and cognitive dysfunction in schizophrenia.

Predictors of functioning in treatment-resistant schizophrenia: the role of negative symptoms and neurocognition

Introduction

Predictors of functioning are well-studied in schizophrenia, but much less so in treatment-resistant schizophrenia (TRS). In this study, we aim to investigate contributions of schizophrenia symptom domains and neurocognition to predict functioning in a TRS population (n = 146).

Methods

Participants were assessed on the Positive and Negative Syndrome Scale (PANSS), to calculate scores for five symptom factors (Positive, Negative, Cognitive, Depressive and Hostility) and two negative symptom constructs (Diminished Expressivity (DE), and Social Anhedonia (SA) as part of the Motivation and Pleasure-related dimension), based on a previously validated model, modified in accordance with EPA guidelines on negative symptoms assessment. Neurocognition was assessed with symbol coding and digit sequencing tasks from the Brief Assessment of Cognition in Schizophrenia (BACS). Functioning was assessed with the Social and Occupational Functioning Assessment Scale (SOFAS), employment status and World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0). Multiple regression analyses were performed on psychopathology scores and BACS scores against all three measures of functioning, controlling for age and sex. For WHODAS, regression with PANSS scores of significant symptom factors were also performed.

Results

A lower severity of negative symptoms in the SA dimension was the strongest predictor of higher functioning across all three functioning measures. Neurocognition, in particular processing speed and attention assessed on the symbol coding task, predicted employment. A lower severity of somatic concerns and depressive symptoms was associated with lesser self-reported disability on WHODAS.

Discussion

This study represents a first attempt at elucidating significant predictors of functioning in TRS. We highlight negative symptoms and neurocognition as important treatment targets to improve functioning in TRS, consistent with previous studies in general schizophrenia.

Promoting safer and wider worldwide use of clozapine

This issue focuses on the past, the present and the future of clozapine. Of the 43 clozapine articles, nine are historical articles dealing with the past, 29 deal with the present and five with laboratory assays which may influence its future use. These 43 articles include 219 different authors from 56 countries/regions and five continents.

Modeling the effects of treatment resistance and anticholinergic burden on cognitive function domains in patients with schizophrenia

The contribution of anticholinergic burden to cognitive function in patients with treatment resistant schizophrenia (TRS) is uncertain. This case-control study aims to comprehensively examine the association between treatment resistance and cognitive functions and the contribution of anticholinergic burden in patients with schizophrenia. Anticholinergic burden of all patients was calculated using the Anticholinergic Cognitive Burden scale. Exploratory Factor Analysis of 11 cognitive assessments identified four cognitive domains: verbal memory, attention and general cognitive functions, visual memory and processing speed, and executive function. Two structural equation models (SEM) examined the relationship of TRS and these cognitive functions with, and without considering anticholinergic burden. A total of 288 participants were included (TRS N=111, non-TRS N=177). Patients with TRS performed poorer than the non-TRS group only in the executive function domain. Anticholinergic burden contributed significantly to the attention and general cognitive functions, visual memory and processing speed, and executive function. The impact of TRS on executive function was no longer significant after adding anticholinergic burden to the SEM. Results suggested that anticholinergic burden contributes to a wide range of cognitive function impairment in patients with schizophrenia and is likely to be part of the apparent differences of cognitive function between TRS and non-TRS.