Mechanism of clozapine-induced agranulocytosis : current status of research and implications for drug development

Polygenic overlap with granulocyte counts identifies novel loci for clozapine metabolism and clozapine-induced agranulocytosis

While clozapine is the most effective antipsychotic drug, its use is limited due to hematological adverse effects involving the reduction of granulocyte counts with potential life-threatening agranulocytosis. It is not yet possible to predict or prevent the risk of agranulocytosis, and the mechanisms are unknown but likely related to clozapine metabolism. Genome-wide association studies (GWASs) of clozapine metabolism and clozapine-induced agranulocytosis have identified few genetic loci. We used the largest available GWAS summary statistics of clozapine metabolism (clozapine-to-norclozapine ratio) and clozapine-induced agranulocytosis, applying the conditional false discovery rate (condFDR) method to increase power for genetic discovery by conditioning on granulocyte counts variants. To investigate potential causal effects of shared loci, we performed Mendelian Randomization analyses. After conditioning on granulocyte counts, we identified two novel loci associated with clozapine-to-norclozapine ratio. These loci were significantly associated with clozapine metabolism in a validation sample of 392 clozapine-treated individuals. For clozapine-induced agranulocytosis, five loci were identified after conditioning on granulocyte counts. These five loci were significantly associated with reduced granulocyte counts in a small independent sample of clozapine-treated individuals. Genetic liability to slow clozapine metabolism (high clozapine-to-norclozapine ratio) showed evidence of a causal effect on reduced neutrophil counts, and genetic liability to low neutrophil counts exhibited weak evidence of a causal effect on clozapine-induced agranulocytosis. Our findings of shared genetic variants associated with clozapine metabolism and granulocyte counts may form the basis for developing prediction models for clozapine-induced agranulocytosis.

Characterization of the atypical antipsychotic drug aripiprazole cytotoxicity in the neutrophil model cell line HL-60

Atypical antipsychotics are widely used for the treatment of mental and behavioral disorders such as bipolar disorder, obsessive-compulsive disorder, and schizophrenia. However, these drugs can occasionally induce neutropenia or agranulocytosis, characterized by a significant reduction in circulating neutrophils, the primary white blood cells responsible for immune responses. This drug-induced neutropenia poses a considerable risk of life-threatening infections. However, the precise mechanism by which atypical antipsychotics induce neutropenia remains unclear. This study investigates the effects of four atypical antipsychotics, namely - aripiprazole, clozapine, olanzapine, and quetiapine - on the human neutrophil model cell line HL-60. These drugs, which modulate dopamine receptor signaling alongside other mechanisms, were analyzed for their effects. Among these, aripiprazole - but not the others - uniquely induced apoptosis in a dose-dependent manner, accompanied by an increased expression of pro-apoptotic genes - BAK, BCL10, and caspase-3. Moreover, our study elucidates that while differentiated HL-60 cells express D1-like and D2-like dopamine receptors, aripiprazole's cytotoxic effects appear to operate through dopamine-independent pathways and significantly reduce phosphorylated Src family kinase levels. Our results align with previous studies suggesting that aripiprazole exhibits cytotoxic properties in neutrophils. Nevertheless, further investigations are warranted to investigate the mechanisms underlying aripiprazole-induced apoptosis in neutrophils.

Neutrophil/lymphocyte ratio is increased in the acute phase of schizophrenia and regardless the use and types of antipsychotic drugs

BACKGROUND

It has been found that patients with schizophrenia are often accompanied by concomitant changes in inflammation levels during acute exacerbations, and some studies have suggested that the inflammatory indices neutrophil/lymphocyte ratio (NLR), platelet/lymphocyte ratio (PLR), and monocyte/lymphocyte ratio (MLR) may be biomarkers of acute exacerbations in schizophrenia; however, few studies have simultaneously explored the differences in these inflammatory indices in the drug-free patients with schizophrenia in acute phase (DSA), medicated patients with schizophrenia in acute phase (MSA), medicated patients with schizophrenia in remission period (MSR), as well as the effects of different antipsychotic medications on inflammatory indices.

METHOD

A total of 651 subjects including 184 healthy controls (HC), 167 DSA, 119 MSA, and 181 MSR were included in this study. Demographic and disease information was collected from each individual and venous blood was collected to detect immune cells and calculate the inflammatory indices NLR, PLR, and MLR, and statistical methods such as analysis of variance (ANOVA) and multiple comparisons were utilized to explore the alteration of these inflammatory indices under the influence of different antipsychotics and in HC, DSA, MSA, and MSR.

RESULTS

NLR was significantly higher in DSA and MSA than in HC after adjusting the confounders of sex, age, smoking, years of education, marital status, BMI, diabetes, and hypertension. PLR and MLR were not significantly different in patients with schizophrenia and in HC, and were not significantly different in patients with schizophrenia in any group. In MSA and MSR, NLR was positively correlated with disease duration and negatively correlated with the use of mood stabilizers.

CONCLUSIONS

NLR was significantly increased in acute phase of schizophrenia, regardless of use of antipsychotic drugs, but not significantly increased in stable phase, which might be a promising biomarker for acute phase of schizophrenia.

Decoding Clozapine-Induced Agranulocytosis: Unraveling Interactions and Mitigation Strategies

Agranulocytosis represents a severe complication associated with the administration of clozapine. Clozapine is an antipsychotic medication that has demonstrated substantial efficacy in remediating refractory schizophrenia and various other psychiatric disorders. Nonetheless, it is crucial to monitor patients for neutropenia regularly during clozapine therapy. Therefore, this article aimed to delve into the prevalence of agranulocytosis during clozapine treatment by scrutinizing the extant literature to discern trends and correlations. This review endeavored to explore factors such as drug interactions, dose-related factors, duration of treatment, and genetic predispositions that could potentially influence the likelihood of patients developing agranulocytosis while undergoing clozapine therapy. Moreover, this review enunciates the ramifications of agranulocytosis on both patients and healthcare providers and meticulously evaluates the strategies to mitigate this risk and ensure optimal patient outcomes.

Novel Identification of Cysteinyl Derivatives of Toxic Clozapine Nitrenium Ions and the Effect of Valproic Acid on Metabolite Formation: A Study Using Reprocessed High-Resolution Mass Spectra of Analyzed Therapeutic Drug Monitoring Samples

BACKGROUND

Clozapine (CLZ) use is hampered by the risk of granulocyte toxicity, which is associated with the formation of nitrenium ions and the concurrent use of valproic acid (VPA). These highly reactive nitrenium ions cannot be measured in vivo. Instead, deactivated cysteinyl conjugates may potentially be detected. The aim of this study was to develop a novel method for identifying cysteinylated derivates of CLZ nitrenium ions to investigate the effect of VPA on their formation using therapeutic drug monitoring data.

METHODS

A population comprising 93 VPA comedicated and 162 control patients from a therapeutic drug monitoring (TDM) service in Oslo, Norway, was included. Reprocessing of ultraperformance liquid chromatography high-resolution mass spectra (UHPLC-HR-MS) of previously analyzed TDM samples, combined with the assessment of MS/MS fragmentation patterns, was performed to identify the CLZ cysteinyl conjugates. Smoking, which induces CLZ metabolism, was assessed by detecting cotinine in the reprocessed mass spectra.

RESULTS

By reprocessing the UHPLC-HR-MS files of the TDM analyses and reviewing the MS/MS fragment profiles, four cysteinyl conjugates of CLZ were identified. The formations of CLZ cysteinyl (CLZ-Cys 1+ ) and CLZ- N -oxide cysteinyl (CLZ-NOX-Cys 1+ ) were 1.5-fold ( P = 0.038) and 2.1-fold ( P < 0.001) higher in VPA-treated patients than those in the controls. In agreement with previous studies, a 45% reduction in N -desmethylclozapine formation was observed in VPA-treated patients ( P < 0.001).

CONCLUSIONS

A novel method for detecting cysteinyl conjugates of CLZ was developed. Application of this method indicated that VPA significantly increased the formation of CLZ-Cys 1+ metabolites, which might explain the granulocyte toxicity reported after adding VPA to CLZ treatment. The developed method opens new avenues for investigating CLZ toxicity, e.g. by correlating cysteinyl conjugates and granulocyte counts in patients.

Agranulocytosis Associated With Psychiatric Polypharmacy: Lessons Learned From a Clinical Case

Psychiatric polypharmacy involves the use of two or more psychotropic medications to manage a mental and emotional condition. The prevalence of psychotropic polypharmacy has been increasing since the 1990s and has been attributed to the rise in multiple psychiatric conditions presenting in one patient. However, as the prevalence of polypharmacy increases to maximize therapeutic advantages, so does the adverse effect profile of those drugs used in combination, leading to very life-threatening effects such as agranulocytosis. Thus, we report a case of agranulocytosis secondary to polypharmacy in a patient with a history of multiple complex psychiatric conditions.  The patient is a 20-year-old female with a past medical history of major depressive disorder, borderline personality disorder, post-traumatic stress disorder, anxiety disorder, hypothyroidism, and ulcerative colitis. Her psychiatric conditions were managed with multiple medications including chlorpromazine, and clozapine was recently added a month prior to admission. Upon admission, the patient was hemodynamically stable and febrile, with complaints of generalized body aches and myalgia. Laboratory results showed profound leukopenia with a white blood cell count of 1.0x103/uL and a neutrophil number of 0.02x103/uL. The patient was admitted to the hospital for neutropenic sepsis and was aggressively treated with intravenous antibiotics. Her clozapine and chlorpromazine were discontinued. In this report, we discuss the association between chlorpromazine and clozapine use and agranulocytosis, emphasizing the importance of regular monitoring and heightened awareness for patients on these medications. This case also underscores the necessity for cautious polypharmacy medication management in individuals with complex psychiatric conditions, highlighting the potential life-threatening consequences of polypharmacy in this population.

Involvement of Extracellular Vesicles in the Proinflammatory Response to Clozapine: Implications for Clozapine-Induced Agranulocytosis

Most idiosyncratic drug reactions (IDRs) appear to be immune-mediated, but mechanistic events preceding severe reaction onset remain poorly defined. Damage-associated molecular patterns (DAMPs) may contribute to both innate and adaptive immune phases of IDRs, and changes in extracellular vesicle (EV) cargo have been detected post-exposure to several IDR-associated drugs. To explore the hypothesis that EVs are also a source of DAMPs in the induction of the immune response preceding drug-induced agranulocytosis, the proteome and immunogenicity of clozapine- (agranulocytosis-associated drug) and olanzapine- (non-agranulocytosis-associated drug) exposed EVs were compared in two preclinical models: THP-1 macrophages and Sprague-Dawley rats. Compared with olanzapine, clozapine induced a greater increase in the concentration of EVs enriched from both cell culture media and rat serum. Moreover, treatment of drug-naïve THP-1 cells with clozapine-exposed EVs induced an inflammasome-dependent response, supporting a potential role for EVs in immune activation. Proteomic and bioinformatic analyses demonstrated an increased number of differentially expressed proteins with clozapine that were enriched in pathways related to inflammation, myeloid cell chemotaxis, wounding, transforming growth factor-β signaling, and negative regulation of stimuli response. These data indicate that, although clozapine and olanzapine exposure both alter the protein cargo of EVs, clozapine-exposed EVs carry mediators that exhibit significantly greater immunogenicity. Ultimately, this supports the working hypothesis that drugs associated with a risk of IDRs induce cell stress, release of proinflammatory mediators, and early immune activation that precedes severe reaction onset. Further studies characterizing EVs may elucidate biomarkers that predict IDR risk during development of drug candidates. SIGNIFICANCE STATEMENT: This work demonstrates that clozapine, an idiosyncratic drug-induced agranulocytosis (IDIAG)-associated drug, but not olanzapine, a safer structural analogue, induces an acute proinflammatory response and increases extracellular vesicle (EV) release in two preclinical models. Moreover, clozapine-exposed EVs are more immunogenic, as measured by their ability to activate inflammasomes, and contain more differentially expressed proteins, highlighting a novel role for EVs during the early immune response to clozapine and enhancing our mechanistic understanding of IDIAG and other idiosyncratic reactions.

The Tarnished Legacy of a Wonder Drug: Revisiting the Complicated History of Clozapine

Anecdotal evidence of superior efficacy and lack of extrapyramidal symptoms in treating schizophrenia made clozapine a promising therapy in the United States during the early 1970s. In 1975, however, numerous fatal cases of clozapine-related agranulocytosis in Finland nearly ended the drug's development. Convinced of the significant benefits to patients, some clinicians in the United States advocated having clozapine available on a case-by-case humanitarian basis, which eventually helped resurrect the drug for Food and Drug Administration approval in 1989. This article builds on previous literature by utilizing oral histories from clinicians, researchers, and a patient's family member to understand how clozapine was saved. Exploring these stakeholders' perspectives has value to modern clinicians, who underprescribe the drug despite demonstrable benefits for treatment-resistant schizophrenia and suicide prevention.

Outcome of COVID-19 mRNA Vaccination in Patients Treated With Clozapine WHO Previously Went Through SARS-COV-2 Infection

BACKGROUND

The outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic had multiple consequences for the health care system, especially for patients with mental illnesses. Schizophrenia patients particularly appear to have a higher risk of complications due to coronavirus-19 (COVID-19). Clozapine remains the gold standard for treatment-resistant schizophrenia (TRS). However, the COVID-19 pandemic had an important negative impact on clozapine treatment, mainly because of its administration protocol, which was very difficult to follow during the restrictions imposed in the pandemic, and its side effects in patients with COVID-19 infection. Vaccination is an effective method of avoiding SARS-CoV-2 infection or its severe complications, especially in susceptible populations. Data on adverse events after vaccination against COVID-19 are limited, both in the general population and in schizophrenia patients.

STUDY QUESTION

The study aimed to investigate the safety of COVID-19 vaccination in patients treated with clozapine for hematological parameters.

STUDY DESIGN

We conducted an analytical cross-sectional study between July 1, 2021, and June 30, 2022. We compared 2 groups of COVID-19 vaccinated patients who had previously experienced SARS-CoV-2 infection: The first group was treated with clozapine, whereas the second group was treated with other antipsychotics.

MEASURES AND OUTCOMES

The primary objective was to identify granulocytopenia, leukocytopenia, and lymphocytopenia. The results were measured after the second dose of the Pfizer-BioNTech vaccine.

RESULTS

This study included 100 patients. White blood cell count changes were limited to a few cases of mild granulocytopenia (8.16% in the clozapine group and 3.92% in the nonclozapine group, P = 0.37) with no cases of severe granulocytopenia or agranulocytosis.

CONCLUSIONS

As far as leukocyte counts are concerned, mRNA COVID-19 vaccination seems to be safe in patients treated with clozapine who previously had SARS-CoV-2 infection. Leukocyte changes had no clinical implications.

The Role of Myeloperoxidase in Clozapine-Induced Inflammation: A Mechanistic Update for Idiosyncratic Drug-Induced Agranulocytosis

The risk of idiosyncratic drug-induced agranulocytosis (IDIAG) markedly constrains the use of clozapine, a neuroleptic with unparalleled efficacy. Most clozapine patients experience an early inflammatory response, likely a necessary step in IDIAG onset. However, most patients do not progress to IDIAG, presumably because of the requirement of specific human leukocyte antigen (HLA) haplotypes, T cell receptors, and other unknown factors. We established that clozapine activates inflammasomes and that myeloperoxidase bioactivation of clozapine generates neoantigens, but the connection between these early mechanistic events remained unknown and, thus, was the aim of this work. We found that the myeloperoxidase inhibitor PF-1355 attenuated myeloperoxidase activity in phorbol myristate acetate (PMA)-differentiated THP-1 macrophages, and it also attenuated clozapine-induced release of inflammatory mediators (e.g., IL-1β, CXCL1, and C-reactive protein). In vivo, pretreatment of Sprague Dawley rats with PF-1355 significantly attenuated clozapine-induced increases in neutrophil mobilization from the bone marrow to the blood and spleen, as determined using differential blood counts and flow cytometry. Moreover, the clozapine-triggered release of inflammatory mediators (e.g., IL-1β, calprotectin, CXCL1, and α-1-acid glycoprotein) from the liver, spleen, and bone marrow was dampened by myeloperoxidase inhibition. These data support the working hypothesis that oxidation of clozapine to a reactive metabolite by myeloperoxidase is critical for induction of the inflammatory response to clozapine. Ultimately, a better mechanistic understanding of the early events involved in the immune response to clozapine may elucidate ways to prevent IDIAG, enabling safer, more frequent therapeutic use of this and potentially other highly efficacious drugs.

Role of Oxidative Stress and Reactive Metabolites in Cytotoxicity & Mitotoxicity of Clozapine, Diclofenac and Nifedipine in CHO-K1 Cells In Vitro

BACKGROUND

CHO-K1 cells were used as in vitro model to explore mechanisms of cytotoxicity of the test drugs.

AIM

To provide in vitro data on toxicity mechanisms of clozapine, diclofenac and nifedipine.

OBJECTIVE

Cytotoxic mechanisms of clozapine (CLZ), diclofenac (DIC) and nifedipine (NIF) were studied in CHO-K1 cells in vitro. All three drugs induce adverse reactions in some patients with partially unknown mechanisms.

METHODS

Following the determination of time- and dose-dependency of cytotoxicity by the MTT test, cytoplasmic membrane integrity was explored by the LDH leakage test. Both end-points were further examined in the presence of soft and hard nucleophilic agents, glutathione (GSH) and potassium cyanide (KCN), respectively, and either individual or general cytochrome P450 (CYP) inhibitors, whether CYPcatalysed formation of electrophilic metabolites play a role in the observed cytotoxicity and membrane damage. The generation of reactive metabolites during the incubations was also explored. Formation of malondialdehyde (MDA) and oxidation of dihydrofluorescein (DCFH) were monitored whether peroxidative membrane damage and oxidative stress take place in cytotoxicity. Incubations were also conducted in the presence of chelating agents of EDTA or DTPA to explore any possible role of metals in cytotoxicity by facilitating electron transfer in redox reactions. Finally, mitochondrial membrane oxidative degradation and permeability transition pore (mPTP) induction by the drugs were tested as markers of mitochondrial damage.

RESULTS

The presence of an individual or combined nucleophilic agents significantly diminished CLZand NIF-induced cytotoxicities, while the presence of both agents paradoxically increased DIC-induced cytotoxicity by a factor of three with the reason remaining unknown. The presence of GSH significantly increased DIC-induced membrane damage too. Prevention of membrane damage by the hard nucleophile KCN suggests the generation of a hard electrophile upon DIC and GSH interaction. The presence of CYP2C9 inhibitor sulfaphenazole significantly diminished DIC-induced cytotoxicity, probably by preventing the formation of 4-hydroxylated metabolite of DIC, which further converts to an electrophilic reactive intermediate. Among the chelating agents, EDTA caused a marginal decrease in CLZ-induced cytotoxicity, while DIC-induced cytotoxicity was amplified by a factor of five. Both reactive and stable metabolites of CLZ could be detected in the incubation medium of CLZ with CHO-K1 cells, which are known to have low metabolic capacity. All three drugs caused a significant increase in cytoplasmic oxidative stress by means of DCFH oxidation, which was confirmed by increased MDA from cytoplasmic as well as mitochondrial membranes. The addition of GSH paradoxically and significantly increased DICinduced MDA formation, in parallel with the increase in membrane damage when DIC and GSH combined.

CONCLUSION

Our results suggested that the soft electrophilic nitrenium ion of CLZ is not responsible for the observed in vitro toxicities, and this may originate from a relatively low amount of the metabolite due to the low metabolic capacity of CHO-K1. A hard electrophilic intermediate may contribute to cellular membrane damage incubated with DIC, while a soft electrophilic intermediate seems to exacerbate cell death by a mechanism other than membrane damage. A significant decrease in cytotoxicity of NIF by GSH and KCN suggested that both soft and hard electrophiles contribute to NIF-induced cytotoxicity. All three drugs induced peroxidative cytoplasmic membrane damage, while only DIC and NIF induced peroxidative mitochondrial membrane damage, which suggested mitochondrial processes may contribute to adverse effects of these drugs in vivo.

Clozapine-specific proliferative response of peripheral blood-derived mononuclear cells in Japanese patients with clozapine-induced agranulocytosis

BACKGROUND

Although clozapine-induced granulocytopenia (CIG) is less severe than clozapine-induced agranulocytosis (CIA), and some patients with CIG may not go on to develop serious complications, clozapine is discontinued in cases of both CIA and CIG. Understanding the pathogenic mechanisms of CIA/CIG could provide better management of clozapine therapy. Recently, as a mechanistic insight into adaptive immune systems, European groups reported clozapine-specific proliferative responses and clozapine-specific T cells using blood taken from patients with CIA and/or CIG.

AIMS

The aims of our study are to support this mechanistic evidence and to investigate the difference in the lymphocyte response to clozapine between patients with CIG and those with CIA.

METHODS

Lymphocyte stimulation tests (LSTs) were conducted using CD25-positive cell-depleted peripheral blood-derived mononuclear cells (PBMCs) isolated from blood of four Japanese patients with CIA, four patients with CIG, and nine clozapine-tolerant subjects.

RESULTS

Three of four patients with CIA and one of four patients with CIG showed proliferative responses to clozapine with a stimulation index of greater than 2. In contrast, none of the nine clozapine-tolerant subjects showed any response to clozapine. Olanzapine did not stimulate PBMCs of patients with CIA, patients with CIG, or clozapine-tolerant subjects.

CONCLUSIONS

Clozapine- and CIA-specific lymphocyte reactions in a Japanese population provided supportive evidence that the pathogenesis of CIA is based on adaptive immune reactions. In addition, patients with CIG who show a positive response to an LST may at the very least not be chosen for clozapine-rechallenge and further prospective studies are desirable to verify this hypothesis.

Adverse Drug Reactions in Relation to Clozapine Plasma Levels: A Systematic Review

Clozapine is the gold standard for treatment-resistant schizophrenia. Serious and even life-threatening adverse effects, mostly granulocytopenia, myocarditis, and constipation, are of great clinical concern and constitute a barrier to prescribing clozapine, thus depriving many eligible patients of a lifesaving treatment option. Interestingly, clozapine presents variable pharmacokinetics affected by numerous parameters, leading to significant inter- and intra-individual variation. Therefore, therapeutic drug monitoring of plasma clozapine levels confers a significant benefit in everyday clinical practice by increasing the confidence of the prescribing doctor to the drug and the adherence of the patient to the treatment, mainly by ensuring effective treatment and limited dose-related side effects. In the present systematic review, we aimed at identifying how a full range of adverse effects relates to plasma clozapine levels, using the Jadad grading system for assessing the quality of the available clinical evidence. Our findings indicate that EEG slowing, obsessive-compulsive symptoms, heart rate variability, hyperinsulinemia, metabolic syndrome, and constipation correlate to plasma clozapine levels, whereas QTc, myocarditis, sudden death, leucopenia, neutropenia, sialorrhea, are rather unrelated. Rapid dose escalation at the initiation of treatment might contribute to the emergence of myocarditis, or leucopenia. Strategies for managing adverse effects are different in these conditions and are discussed accordingly.

Reduction in Absolute Neutrophil Counts in Patient on Clozapine Infected with COVID-19

Despite its severe adverse effects, such as agranulocytosis, clozapine is the primary treatment for treatment-resistant schizophrenia. The established clozapine monitoring system has contributed to reducing agranulocytosis incidence and mortality rates. However, the pandemic coronavirus disease 2019 (COVID-19) has caused changes in the monitoring system. This review aimed to assess the current evidence on the neutrophil changes in the patient on clozapine treatment and infected with COVID-19. Individual cases reported various absolute neutrophil count (ANC) levels, normal, reduced, or elevated. No agranulocytosis case was reported. One case had a borderline moderate-severe ANC level, but the patient was in the 18-week period of clozapine treatment. A cumulative analysis of case the series initially reported inconclusive results. However, a more recent study with a larger sample size reported a significant reduction in the ANC during COVID-19 infection. Nevertheless, this effect is transient as no significant difference was found between the baseline and the post-infection period in ANC levels. In conclusion, COVID-19 is associated with a temporary reduction in ANC levels. The results supported the recommendation to reduce the frequency of clozapine monitoring in the eligible candidates. However, more data are required to confirm the current findings given the limitations, including study design, sample size, and statistical analysis.

Therapeutic drug monitoring of clozapine in adults with schizophrenia: a review of challenges and strategies

INTRODUCTION

Clozapine (CLZ) is the superior drug in treatment of schizophrenia. Serum concentration of CLZ is associated with clinical response and dose-dependents side effects, where generalized tonic-clonic seizures are most critical. Thus, therapeutic drug monitoring (TDM) of CLZ may guide individual dosing to reach target exposure and prevent dose-dependent side effects. However, current TDM methods are not capable of predicting the risk of agranulocytosis, which is a dose-independent side effect restricting use of CLZ to treatment-resistant schizophrenia (TRS).

AREAS COVERED

The article provides an overview of clinical, pharmacological, and toxicological aspects of CLZ, and the role of TDM as a tool for dose titration and follow-up in patients with TRS. Main focus is on current challenges and strategies in CLZ TDM, including future perspectives on potential identification/analysis of CLZ metabolite biomarkers reflecting the risk of granulocyte toxicity.

EXPERT OPINION

The association between CLZ serum concentration, clinical response and risk of seizures is indisputable. TDM should therefore always guide CLZ dose titration. Development of advanced TDM methods, including biomarkers predicting the risk of granulocyte toxicity might extend TDM to be a tool for deciding which patients that can be treated safely with CLZ, potentially increasing its utility beyond TRS.

Molecular fingerprinting by single cell clone analysis in adverse drug reaction (ADR) assessment

Causality assessment for idiosyncratic ADRs mainly relies on epidemiology, signal detection and less often on proven or plausible mechanistic evidence of the drug at a cellular or organ level. Distinct clones of cells can exist within organs of individual patients, some conferring susceptibility to well recognised adverse drug reactions (ADRs). Recent advances in molecular biology has allowed the development of single cell clonal techniques, including single cell RNA sequencing (scRNA-seq) to molecularly fingerprint ADRs and distinguish between distinct clones of cells within organs in individuals, which may confer differing susceptibilities to ADRs. ScRNA-seq permits molecular fingerprinting of some serious ADRs, mainly in the skin, through identification of directly expressed genes (DEG) of interest within specific clones. Overexpressed DEGs provides an opportunity for targeted treatment strategies to be developed. scRNA-seq could be applied to a number of other ADRs involving tissues that can be biopsied/sampled (including skin, liver, kidney, blood, stem cells) as well as providing a molecular basis for rapid screening of potential therapeutic candidates, which may not otherwise be predictable from class of toxicity/organ involvement. . A framework for putative assessment for ADRs using scRNA-seq is proposed as well as speculating on potential regulatory implications for pharmacovigilance and drug development. Molecular fingerprinting of ADRs using scRNA-seq may allow better targeting for enhanced pharmacovigilance and risk minimisation measures for medicines with appropriate benefit risk profiles, although cost-effectiveness and other factors, such as frequency/severity of individual ADRs and population differences will still be relevant.

The Emerging Role of the Innate Immune Response in Idiosyncratic Drug Reactions

Idiosyncratic drug reactions (IDRs) range from relatively common, mild reactions to rarer, potentially life-threatening adverse effects that pose significant risks to both human health and successful drug discovery. Most frequently, IDRs target the liver, skin, and blood or bone marrow. Clinical data indicate that most IDRs are mediated by an adaptive immune response against drug-modified proteins, formed when chemically reactive species of a drug bind to self-proteins, making them appear foreign to the immune system. Although much emphasis has been placed on characterizing the clinical presentation of IDRs and noting implicated drugs, limited research has focused on the mechanisms preceding the manifestations of these severe responses. Therefore, we propose that to address the knowledge gap between drug administration and onset of a severe IDR, more research is required to understand IDR-initiating mechanisms; namely, the role of the innate immune response. In this review, we outline the immune processes involved from neoantigen formation to the result of the formation of the immunologic synapse and suggest that this framework be applied to IDR research. Using four drugs associated with severe IDRs as examples (amoxicillin, amodiaquine, clozapine, and nevirapine), we also summarize clinical and animal model data that are supportive of an early innate immune response. Finally, we discuss how understanding the early steps in innate immune activation in the development of an adaptive IDR will be fundamental in risk assessment during drug development. SIGNIFICANCE STATEMENT: Although there is some understanding that certain adaptive immune mechanisms are involved in the development of idiosyncratic drug reactions, the early phase of these immune responses remains largely uncharacterized. The presented framework refocuses the investigation of IDR pathogenesis from severe clinical manifestations to the initiating innate immune mechanisms that, in contrast, may be quite mild or clinically silent. A comprehensive understanding of these early influences on IDR onset is crucial for accurate risk prediction, IDR prevention, and therapeutic intervention.

Genetic risk of clozapine-induced leukopenia and neutropenia: a genome-wide association study

BACKGROUND

Clozapine is considered to be the most effective antipsychotic medication for schizophrenia. However, it is associated with several adverse effects such as leukopenia, and the underlying mechanism has not yet been fully elucidated. The authors performed a genome-wide association study (GWAS) in a Chinese population to identify genetic markers for clozapine-induced leukopenia (CIL) and clozapine-induced neutropenia (CIN).

METHODS

A total of 1879 patients (225 CIL cases, including 43 CIN cases, and 1,654 controls) of Chinese descent were included. Data from common and rare single nucleotide polymorphisms (SNPs) were tested for association. The authors also performed a trans-ancestry meta-analysis with GWAS results of European individuals from the Clozapine-Induced Agranulocytosis Consortium (CIAC).

RESULTS

The authors identified several novel loci reaching the threshold of genome-wide significance level (P < 5 × 10-8). Three novel loci were associated with CIL while six were associated with CIN, and two T cell related genes (TRAC and TRAT1) were implicated. The authors also observed that one locus with evidence close to genome-wide significance (P = 5.08 × 10-8) was near the HLA-B gene in the major histocompatibility complex region in the trans-ancestry meta-analysis.

CONCLUSIONS

The associations provide novel and valuable understanding of the genetic and immune causes of CIL and CIN, which is useful for improving clinical management of clozapine related treatment for schizophrenia. Causal variants and related underlying molecular mechanisms need to be understood in future developments.

Clozapine Metabolism is Associated With Absolute Neutrophil Count in Individuals With Treatment-Resistant Schizophrenia

Up to one-third of those with schizophrenia fail to respond to standard antipsychotics and are considered to have treatment-resistant schizophrenia, a condition for which clozapine is the only evidence-based medication. While up to 60% of treated individuals obtain therapeutic benefits from clozapine, it is currently underprescribed worldwide, partly because of concerns related to its broad adverse effect profile. In particular, the potential effects of clozapine on the immune system have gained relevance after a recent study showed that drug plasma concentrations were inversely correlated with neutrophil counts in individuals routinely undergoing treatment. Seeking to investigate this relationship in more detail, we extracted metabolic, immune, and genetic data from a UK cohort of long-term clozapine users linked to a clozapine monitoring service, CLOZUK2 (N = 208). Whilst a correlation analysis was compatible with the original results, a multiple linear regression accounting for dose and other confounding factors additionally allowed us to estimate the decrease in absolute neutrophil counts to approximately 141 cells/mm3 for every 0.1 mg/L increase in clozapine concentration. However, this association was attenuated after controlling for the metabolic ratio between clozapine and its main metabolite, norclozapine, which was itself negatively associated with neutrophil concentrations. Further analyses revealed that these relationships are likely moderated by genetic factors, as three pharmacogenomic SNPs previously associated to norclozapine plasma concentrations and the metabolic ratio (rs61750900, rs2011425 and rs1126545) were shown to be independently associated with a variation in neutrophil counts of about 400 cells/mm3 per effect allele. Such results are compatible with an effect of norclozapine, but not necessarily clozapine, on immune cell counts, and highlight the need for further investigations into the potential role of genetic determinants of clozapine pharmacokinetics in the occurrence of adverse effects during treatment.

HLA-DQB1 6672G>C (rs113332494) is associated with clozapine-induced neutropenia and agranulocytosis in individuals of European ancestry

The atypical antipsychotic clozapine is the only effective medication for treatment-resistant schizophrenia. However, it can also induce serious adverse drug reactions, including agranulocytosis and neutropenia. The mechanism by which it does so is largely unknown, but there is evidence for contributing genetic factors. Several studies identified HLA-DQB1 variants and especially a polymorphism located in HLA-DQB1 (6672G>C, rs113332494) as associated with clozapine-induced agranulocytosis and neutropenia. We analysed the risk allele distribution of SNP rs113332494 in a sample of 1396 controls and 178 neutropenia cases of which 60 developed agranulocytosis. Absolute neutrophil counts of 500/mm3 and 1500/mm3 were used for defining agranulocytosis and neutropenia cases, respectively. We also performed association analyses and analysed local ancestry patterns in individuals of European ancestry, seeking replication and extension of earlier findings. HLA-DQB1 (6672G>C, rs113332494) was associated with neutropenia (OR = 6.20, P = 2.20E-06) and agranulocytosis (OR = 10.49, P = 1.83E-06) in individuals of European ancestry. The association signal strengthened after including local ancestry estimates (neutropenia: OR = 10.38, P = 6.05E-08; agranulocytosis: OR = 16.31, P = 1.39E-06), with effect sizes being considerably larger for agranulocytosis. Using local ancestry estimates for prediction, the sensitivity of rs113332494 increased from 11.28 to 55.64% for neutropenia and from 16.67 to 53.70% for agranulocytosis. Our study further strengthens the evidence implicating HLA-DQB1 in agranulocytosis and neutropenia, suggesting components of the immune system as contributing to this serious adverse drug reaction. Using local ancestry estimates might help in identifying risk variants and improve prediction of haematological adverse effects.

A systematic review and meta-analysis of the association between clozapine and norclozapine serum levels and peripheral adverse drug reactions

RATIONALE

Clozapine is the most effective antipsychotic for treatment-refractory schizophrenia for reducing positive psychotic symptoms. It is associated with a reduction in hospitalisation and overall mortality. In spite of this, clozapine remains underutilised due to its complex adverse drug reaction (ADR) profile.

OBJECTIVE

This systematic review aims to investigate the association of clozapine and norclozapine serum levels, and peripheral ADRs.

METHODS

Studies were searched from four electronic databases (PubMed, EMBASE, PsycINFO and CINAHL) from inception to 12 June 2020. Studies were included if they had adult patients, provided data on steady-state trough clozapine or norclozapine levels and reported on clozapine-associated ADRs. Pregnant women, case reports and series were excluded.

RESULTS

A statistically significant correlation was found for clozapine serum levels and triglycerides (n = 70; r = 0.303, 95% CI 0.0119-0.546, p = 0.042), heart rate (n = 137; r = 0.269, 95% CI 0.0918-0.486, p = 0.035), and overall combined ADRs (n = 160; r = 0.264, 95% CI 0.110-0.405, p = 0.001), but not for absolute neutrophil count (n = 223; r = - 0.164, 95% CI - 0.529-0.253, p = 0.444) or total white cell count (n = 18; r = 0.0176, 95% CI - 0.203-0.237, p = 0.878). Interestingly, norclozapine serum levels were found to be statistically correlated to triglycerides (n = 120; r = 0.211, 95% CI 0.0305-0.378, p = 0.022), total cholesterol (n = 120; r = 0.272, 95% CI 0.0948-0.432, p = 0.003) and weight gain (n = 118; r = 0.208, 95% CI 0.0261-0.377, p = 0.025).

CONCLUSIONS

Heart rate, triglycerides and combined ADRs are significantly correlated with clozapine levels, and triglycerides, total cholesterol and weight gain with norclozapine levels. Future prospective, randomised controlled studies are needed to identify the cause-effect relationship between clozapine levels and peripheral ADRs.

Clozapine re-challenge and initiation following neutropenia: a review and case series of 14 patients in a high-secure forensic hospital

OBJECTIVE

Clozapine remains the most effective intervention for treatment resistant schizophrenia; however, its use is prohibited following neutropenias. We review neutrophil biology as applied to clozapine and describe the strategies to initiate clozapine following neutropenia used in a case series of 14 consecutive patients rechallenged in a United Kingdom (UK) high-secure psychiatric hospital. We examine outcomes including the use of seclusion and transfer.

METHODS

A case series of 14 male patients with treatment resistant schizophrenia treated with clozapine despite previous episodes of neutropenia between 2006 and 2015 is presented. Data were collected during 2015 and 2019. Using this routinely collected clinical data, we describe the patient characteristics, causes of neutropenia, the strategies used for rechallenging with clozapine and clinical outcomes.

RESULTS

Previous neutropenias were the result of benign ethnic neutropenia, clozapine, other medications and autoimmune-related. Our risk mitigation strategies included: granulocyte-colony stimulating factor (G-CSF), lithium and watch-and-wait. There were no serious adverse events; at follow up half of the patient's had improved sufficiently to transfer them to conditions of lesser security. There were dramatic reductions in the use of seclusion.

CONCLUSION

Even in this extreme group, clozapine can be safely and effectively re/initiated following neutropenias, resulting in marked benefits for patients. This requires careful planning based on an understanding of neutrophil biology and the aetiology of the specific episode of neutropenia.

Identification of a novel polymorphism associated with reduced clozapine concentration in schizophrenia patients-a genome-wide association study adjusting for smoking habits

Clozapine (CLZ) is the superior antipsychotic drug for treatment of schizophrenia, but exhibits an extensive interpatient pharmacokinetic variability. Here, we conducted a genome-wide association study (GWAS) of CLZ serum concentration adjusting for known smoking habits, which is a major nongenetic factor reducing CLZ levels. The study included 484 patients with 10,283 steady-state serum concentrations of CLZ and N-desmethylclozapine, prescribed dosing, co-medications and known smoking habits (n = 422; 9284 serum samples) from a therapeutic drug monitoring (TDM) service. The GWAS analyses were performed with and without smoking habits as covariate, where possible hits were assessed in relation to the target CLZ concentration range applied in the TDM service (300-2500 nmol/L). The smoking-independent analysis of N-desmethylclozapine serum concentration and the CLZ-to-N-desmethylclozapine ratio replicated the previously identified locus on chromosome 4. After adjusting for smoking habits in patients confirmed as 'smokers' (61%) or 'nonsmokers' (39%), a novel variant (rs28379954; minor T>C allele frequency 4.1%; 7.6% CT carriers in the population) within the gene encoding the nuclear factor 1 B-type (NFIB) was significantly associated with reduced CLZ serum concentration (p = 1.68 × 10-8, beta = -0.376; explained variance 7.63%). There was no significant association between rs28379954 and N-desmethylclozapine concentration in the GWAS analysis (p = 5.63 × 10-5). The fraction of CLZ TDM samples below 300 nmol/L was significantly higher in carriers vs. noncarriers of the rs28379954 minor C allele [12.0% (95% CI: 9.4-14.7) vs. 6.2% (95% CI: 5.7-6.8), p < 0.001]. We identified a novel variant in the NFIB gene associated with reduced CLZ levels and increased risk of subtherapeutic serum concentrations. This warrants testing of clinical relevance of screening for this gene variant, and also experimental studies to investigate the biological mechanisms of NFIB involvement in CLZ pharmacokinetics.

Clozapine rechallenge and initiation despite neutropenia- a practical, step-by-step guide

Clozapine remains the only drug treatment likely to benefit patients with treatment resistant schizophrenia. Its use is complicated by an increased risk of neutropenia and so there are stringent monitoring requirements and restrictions in those with previous neutropenia from any cause or from clozapine in particular. Despite these difficulties clozapine may yet be used following neutropenia, albeit with caution. Having had involvement with 14 cases of clozapine use in these circumstances we set out our approach to the assessment of risks and benefits, risk mitigation and monitoring with a practical guide.

Genetics of clozapine-associated neutropenia: recent advances, challenges and future perspective

Clozapine is the only effective antipsychotic for treatment-resistant schizophrenia but remains widely under prescribed, at least in part due to its potential to cause agranulocytosis and neutropenia. In this article, we provide an overview of the current understanding of the genetics of clozapine-associated agranulocytosis and neutropenia. We now know that the genetic etiology of clozapine-associated neutropenia is complex and is likely to involve variants from several genes including HLA-DQB1, HLA-B and SLCO1B3/SLCO1B7. We describe recent findings relating to the Duffy-null genotype and its association with benign neutropenia in individuals with African ancestry. Further advances will come from sequencing studies, large, cross-population studies and in understanding the molecular mechanisms underlying these associations.

Psychological Considerations in Hematopoietic Stem Cell Transplantation

BACKGROUND

In recent decades, advances in transplantation medicine, and improved posttransplant care have reduced morbidity and mortality from hematopoietic stem cell transplantations (HSCTs). However, patients undergoing HSCT report a high prevalence of psychological distress, which can negatively impact recovery, function, and health outcomes, including mortality and higher risk of graft vs. host disease. Appropriate assessment and management of these psychological symptoms lead to better engagement with treatment and a variety of superior health outcomes.

OBJECTIVE

We provide a narrative review of the psychological challenges that accompany HSCT and suggest management approaches to equip psychiatric consultants involved in the care of this patient population.

METHODS

We reviewed published work in PubMed, PsycInfo, and Scopus electronic databases on the common psychological challenges in HSCT, their vulnerability factors, as well as practical interventions for managing these challenges.

RESULTS

We outline the phases of the HSCT hospitalization and discuss common psychological challenges, such as depression, delirium, and post-traumatic stress reactions that accompany HSCT. We suggest an approach to psychiatric consults during the HSCT hospitalization and discuss practical interventions for managing psychological challenges in this population.

CONCLUSIONS

Though pharmacological and behavioral interventions have been successfully used to treat psychosocial challenges in HSCT, further research is needed to understand the optimal psychiatric assessment tools, treatment strategies, and the long-term psychiatric care needed to address psychiatric comorbidities in this growing patient population.

Sodium valproate and clozapine induced neutropenia: A case control study using register data

BACKGROUND

The use of clozapine is limited due to the occurrence of neutropenia, and the rare but life threatening adverse event of agranulocytosis. There is little epidemiological research into clinical factors that may impact on this risk. We conducted a case control study examining the clinical risk factors for neutropenia patients treated with clozapine.

METHOD

A case-control study was conducted within a database of anonymised electronic clinical records. All patients who discontinued clozapine due to a neutropenic event were included as cases. Matched controls were selected from patients with a documented clozapine exposure at the time of the clozapine neutropenic event of the case patient, matched by duration of clozapine treatment.

RESULTS

136 cases and 136 controls were included. In multivariable analysis, the concurrent use of sodium valproate was associated with neutropenia (Odds Raito (OR) 2.28, 95%CI: 1.27-4.11, p=0.006). There was a dose-response effect, with greater associations for higher doses. Patients who discontinued clozapine due to neutropenia were more likely to be of black ethnicity (OR 2.99, p<0.001), were younger (t=5.86, df=267, p<0.001), and received lower doses of clozapine (t=-2.587, p=0.01) than those who did not develop neutropenia.

CONCLUSION

We identified an association between the concurrent use of sodium valproate and an increased risk of clozapine associated neutropenia. These results, taken in combination with the results from previous case series, suggest that the risk of clozapine associated neutropenia could be reduced by avoiding concurrent valproate treatment.

Clozapine and blood dyscrasia

Clozapine is an effective antipsychotic medication but is associated with agranulocytosis, neutropenia and leucopenia. The reintroduction of clozapine improved management of treatment-resistant schizophrenia, yet resulted in a paradoxical situation whereby the risk of blood dyscrasias is rigorously managed but other adverse effects (e.g. seizures, cardiovascular complications) are less well monitored. Monitoring of weight, lipids, plasma glucose and other metabolic parameters is recommended. There is also a need to reconsider routine haematological monitoring with other medications associated with blood dyscrasia (e.g. phenothiazines, carbamazepine). In particular, individuals who develop clozapine-induced blood dyscrasia may require haematological monitoring during treatment with other antipsychotics.

Correlation Between Serum Concentrations of N-Desmethylclozapine and Granulocyte Levels in Patients with Schizophrenia: A Retrospective Observational Study

BACKGROUND

Clozapine is restricted to use in patients with treatment-refractory schizophrenia due to the risk of a serious drop in absolute neutrophil granulocyte count (ANC). The formation of reactive, unstable metabolites (adducts) has been suggested as a mechanism of clozapine-induced granulocyte decline. These adducts are not detectable in vivo, but stable clozapine metabolites could potentially be indirect pharmacokinetic measures of adduct formation.

OBJECTIVE

The present retrospective observational study investigated the correlation between concentrations of N-desmethylclozapine, the major stable clozapine metabolite, and ANC in a real-life population of clozapine-treated patients.

METHODS

Patients were included from a therapeutic drug monitoring service at the Center for Psychopharmacology, Diakonhjemmet Hospital, Oslo, Norway, between March 2005 and December 2015. Information about clozapine and N-desmethylclozapine steady-state trough concentrations, as well as accompanying measurements of ANC, were collected from the laboratory database. Correlations of serum concentrations of N-desmethylclozapine and clozapine (and their respective ratios) with ANC were investigated by linear mixed-model analysis.

RESULTS

Overall, 129 patients with 855 measurements of clozapine/N-desmethylclozapine concentrations and ANC (range 0.9-19 × 10⁹ cells/L, median 4.6) were included. Concentrations of N-desmethylclozapine, but not clozapine, correlated significantly and positively with ANC (estimated model slope 0.0011 × 10⁹ cells/L/nM; p = 0.002), and the N-desmethylclozapine/clozapine ratio also positively correlated with ANC (p = 0.040).

CONCLUSIONS

N-Desmethylclozapine level and ANC significantly correlated in this real-life population of schizophrenia patients. The positive correlation, which was also present for the metabolic ratio, might reflect reduced clozapine availability for the formation of reactive metabolites potentially affecting granulocyte level. However, as our findings were based on ANC mainly within the reference range, this hypothesis should be studied further in clozapine-treated patients with neutropenia or agranulocytosis.

Genome-wide common and rare variant analysis provides novel insights into clozapine-associated neutropenia

The antipsychotic clozapine is uniquely effective in the management of schizophrenia; however, its use is limited by its potential to induce agranulocytosis. The causes of this, and of its precursor neutropenia, are largely unknown, although genetic factors have an important role. We sought risk alleles for clozapine-associated neutropenia in a sample of 66 cases and 5583 clozapine-treated controls, through a genome-wide association study (GWAS), imputed human leukocyte antigen (HLA) alleles, exome array and copy-number variation (CNV) analyses. We then combined associated variants in a meta-analysis with data from the Clozapine-Induced Agranulocytosis Consortium (up to 163 cases and 7970 controls). In the largest combined sample to date, we identified a novel association with rs149104283 (odds ratio (OR)=4.32, P=1.79 × 10^-8), intronic to transcripts of SLCO1B3 and SLCO1B7, members of a family of hepatic transporter genes previously implicated in adverse drug reactions including simvastatin-induced myopathy and docetaxel-induced neutropenia. Exome array analysis identified gene-wide associations of uncommon non-synonymous variants within UBAP2 and STARD9. We additionally provide independent replication of a previously identified variant in HLA-DQB1 (OR=15.6, P=0.015, positive predictive value=35.1%). These results implicate biological pathways through which clozapine may act to cause this serious adverse effect.

Pharmacogenomic Study of Clozapine-Induced Agranulocytosis/Granulocytopenia in a Japanese Population

BACKGROUND

Clozapine-induced agranulocytosis (CIA)/clozapine-induced granulocytopenia (CIG) (CIAG) is a life-threatening event for schizophrenic subjects treated with clozapine.

METHODS

To examine the genetic factor for CIAG, a genome-wide pharmacogenomic analysis was conducted using 50 subjects with CIAG and 2905 control subjects.

RESULTS

We identified a significant association in the human leukocyte antigen (HLA) region (rs1800625, p = 3.46 × 10(-9), odds ratio [OR] = 3.8); therefore, subsequent HLA typing was performed. We detected a significant association of HLA-B*59:01 with CIAG (p = 3.81 × 10(-8), OR = 10.7) and confirmed this association by comparing with an independent clozapine-tolerant control group (n = 380, p = 2.97 × 10(-5), OR = 6.3). As we observed that the OR of CIA (OR: 9.3~15.8) was approximately double that in CIG (OR: 4.4~7.4), we hypothesized that the CIG subjects were a mixed population of those who potentially would develop CIA and those who would not develop CIA (non-CIA). This hypothesis allowed the proportion of the CIG who were non-CIA to be calculated, enabling us to estimate the positive predictive value of the nonrisk allele on non-CIA in CIG subjects. Assuming this model, we estimated that 1) ~50% of CIG subjects would be non-CIA; and 2) ~60% of the CIG subjects without the risk allele would be non-CIA and therefore not expected to develop CIA.

CONCLUSIONS

Our results suggest that HLA-B*59:01 is a risk factor for CIAG in the Japanese population. Furthermore, if our model is true, the results suggest that rechallenging certain CIG subjects with clozapine may not be always contraindicated.

Relation of the Allelic Variants of Multidrug Resistance Gene to Agranulocytosis Associated With Clozapine

Clozapine use is associated with leukopenia and more rarely agranulocytosis, which may be lethal. The drug and its metabolites are proposed to interact with the multidrug resistance transporter (ABCB1/MDR1) gene product, P-glycoprotein (P-gp). Among various P-glycoprotein genetic polymorphisms, nucleotide changes in exons 26 (C3435T), 21 (G2677T), and 12 (C1236T) have been implicated for changes in pharmacokinetics and pharmacodynamics of many substrate drugs. In this study, we aimed to investigate the association between these specific ABCB1 polymorphisms and clozapine-associated agranulocytosis (CAA). Ten patients with a history of CAA and 91 control patients without a history of CAA, despite 10 years of continuous clozapine use, were included. Patient recruitment and blood sample collection were conducted at the Hacettepe University Faculty of Medicine, Department of Psychiatry, in collaboration with the members of the Schizophrenia and Other Psychotic Disorders Section of the Psychiatric Association of Turkey, working in various psychiatry clinics. After DNA extraction from peripheral blood lymphocytes, genotyping was performed using polymerase chain reaction and endonuclease digestion. Patients with CAA had shorter duration of clozapine use but did not show any significant difference in other clinical, sociodemographic characteristics and in genotypic or allelic distributions of ABCB1 variants and haplotypes compared with control patients. Among the 10 patients with CAA, none carried the ABCB1 all-variant haplotype (TT-TT-TT), whereas the frequency of this haplotype was approximately 12% among the controls. Larger sample size studies and thorough genetic analyses may reveal both genetic risk and protective factors for this serious adverse event.

New genetic findings lead the way to a better understanding of fundamental mechanisms of drug hypersensitivity

Drug hypersensitivity reactions are an important clinical problem for both health care and industry. Recent advances in genetics have identified a number of HLA alleles associated with a range of these adverse reactions predominantly affecting the skin but also other organs, such as the liver. The associations between abacavir hypersensitivity and HLA-B*57:01 and carbamazepine-induced Stevens-Johnson syndrome and HLA-B*15:02 have been implemented in clinical practice. There are many different mechanisms proposed in the pathogenesis of drug hypersensitivity reactions, including the hapten hypothesis, direct binding to T-cell receptors (the pharmacologic interaction hypothesis), and peptide-binding displacement. A problem with all the hypotheses is that they are largely based on in vitro findings, with little direct in vivo evidence. Although most studies have focused on individual mechanisms, it is perhaps more important to consider them all as being complementary, potentially occurring at the same time with the same drug in the same patient. This might at least partly account for the heterogeneity of the immune response seen in different patients. There is a need to develop novel methodologies to evaluate how the in vitro mechanisms relate to the in vivo situation and how the highly consistent genetic findings with different HLA alleles can be more consistently used for both prediction and prevention of these serious adverse reactions.

Clozapine linked to nanocapsules minimizes tissue and oxidative damage to biomolecules lipids, proteins and DNA in brain of rats Wistar

Clozapine, atypical antipsychotic, can change oxidative stress parameters. It is known that reactive species, in excess, can have a crucial role in the etiology of diseases, as well as, can potentiating adverse effects induce by drugs. The nanocapsules have attracted attention as carriers of several drugs, with consequent reduction of adverse effects. This study aimed to evaluate histopathology and oxidative damage of biomolecules lipids, proteins and DNA in the brain of Wistar rats after treatment with nanocapsules containing clozapine. The study consisted of eight groups of male Wistar rats (n = 6): saline (SAL), free clozapine (CZP) (25 mg/Kg i.p.), blank uncoated nanocapsules (BNC), clozapine-loaded uncoated nanocapsules (CNC) (25 mg/Kg i.p.), blank chitosan-coated nanocapsules (BCSN), clozapine-loaded chitosan-coated nanocapsules (CCSN) (25 mg/Kg i.p.), blank polyethyleneglycol-coated nanocapsules (BPEGN), clozapine-loaded polyethyleneglycol-coated nanocapsules (CPEGN) (25 mg/Kg i.p.). The animals received the formulation once a day for seven consecutive days and euthanized in the eighth day. After euthanasia, the brain was collected and homogenate was processed for further analysis. The histopathology showed less brain tissue damage in nanocapsules-treated groups. The lipid peroxidation and carbonylation of proteins showed a significant increase (p < 0.05) induced by CZP. CNC and CPEGN groups obtained a reduction membrane of lipids damage and nanocapsules-treated groups showed significant improvement protein damage. CZP was able to induce genetic oxidative damage, while the nanocapsules causing less damage to DNA. The findings show that different coatings can act protecting target tissues decreasing oxidative damage, suggesting that the drug when linked to different nanocapsules is able to mitigate the harmful effects of clozapine.

Clozapine treatment of refractory schizophrenia during essential chemotherapy: a case study and mini review of a clinical dilemma

BACKGROUND

Clozapine remains the antipsychotic of choice for refractory schizophrenia. Given the particular side effects of clozapine including neutropenia and myelosuppression, safety and efficacy of add-on chemotherapy for patients who are already under clozapine treatment remain unknown.

OBJECTIVE

We present evidence from a patient with a diagnosis of refractory schizophrenia on clozapine medication, who required essential chemotherapy for chronic lymphocytic leukemia (CLL). We have also reviewed literature regarding this challenging clinical dilemma.

METHOD

We report details about a patient with treatment-resistant schizophrenia who was given chemotherapy (fludarabine, cyclophosphamide and rituximab) for CLL in the course of concomitant treatment with clozapine and granulocyte-colony stimulating factor (G-CSFs). In addition, we have reviewed literature using the PUBMED data base.

RESULTS

Current evidence remains insufficient to provide authoritative guide to clinicians regarding the efficacy and safety of the combined use of clozapine and chemotherapy. However, general conclusion from our case and of the published evidence is that a combination of clozapine use and chemotherapeutic agents do not cause additional hematological worsening with no decreasing efficacy concerns raised.

CONCLUSION

Continuing with clozapine in the course of chemotherapy may be relatively safer for patients who responded well to clozapine concomitant with G-CSF treatment.

Late onset clozapine induced agranulocytosis

Agranulocytosis is defined as an absolute neutrophil count less than 100/mm(3) in association with infectious disease. The risk of agranulocytosis is 0.38% of all clozapine treated cases and there is a relatively lesser incidence in Indian population. The risk of clozapine-induced agranulocytosis and neutropenia is highest in the first 6 months and higher in the initial 18 months after the onset of treatment. There have been very few reports of neutropenia and agranulocytosis after this period. There have so far been no reports of late onset clozapine induced agranulocytosis has been reported from India. A case of late onset clozapine induced agranulocytosis with possible mechanism of the same is reported.

Clozapine promotes the proliferation of granulocyte progenitors in the bone marrow leading to increased granulopoiesis and neutrophilia in rats

Clozapine is an atypical antipsychotic that is limited in its use due to the risk of idiosyncratic agranulocytosis. The bone marrow is suspected to be the site of the reaction, and indirect measurements in patients suggest that neutrophil production and maturation are altered in the marrow by clozapine. Specifically, the majority of patients have elevated neutrophil counts at the start of treatment, often paired with increased serum granulocyte-colony stimulating factor (G-CSF). Employing a rat model of clozapine treatment, we set out to determine if the neutrophilia observed at the start of treatment is characteristic of G-CSF-associated bone marrow stimulation. Female Sprague-Dawley rats were treated with 30 mg/kg/day of clozapine for 10 days, and sustained neutrophilia was evident after 1 week of treatment paired with spikes in G-CSF. Within the bone marrow, clozapine was found to induce proliferation of the granulocyte progenitor colonies as measured by a methylcellulose assay. This led to elevated granulopoiesis observed by H&E and myeloperoxidase staining of bone marrow slices. Increased release of neutrophils from the marrow to the circulation was measured through 5-bromo-2'-deoxyuridine labeling in vivo, and these neutrophils appeared to be less mature based on (a) a decrease in the nuclear lobe count and (b) increased expression of surface CD62L. Furthermore, faster transit of the neutrophils through the marrow was suggested by a shift toward elevated numbers of neutrophils in the bone marrow maturation pool and increased CD11b and CD18 staining on the less mature neutrophils residing in the marrow. Taken together, these data indicate that clozapine stimulates the bone marrow to produce more neutrophils in a manner that is characteristic of endogenous G-CSF stimulation, and it is consistent with the inflammatory response observed in patients treated with clozapine.

Clozapine-Induced Febrile Neutropenia and Cellulitis

Clozapine is one of the atypical antipsychotics and is frequently prescribed to patients with treatment-resistant schizophrenia. Agranulocytosis is a major side effect that may lead to death, which limits its use. This is a case report of a patient that developed febrile neutropenia and cellulitis after treatment with clozapine for 20 weeks.

Clozapine treatment of patients with refractory schizophrenia, concurrent dengue infection and hematological abnormalities: three case reports

BACKGROUND

Dengue is a febrile illness that is most common in tropical areas but is recognized worldwide as one of the most important arbovirus diseases of humans. This febrile illness generally has a course with mild alterations in white blood cell count, but there are also rare cases of severe neutropenia or agranulocytosis during dengue infection. Clozapine (CLZ) remains the most effective treatment for schizophrenia, but because of its poor side effect profile, in particular due to the increased risk of neutropenia and agranulocytosis, it is generally used for patients whose condition responds poorly to other antipsychotics.

METHODS

We report three cases of dengue infection in patients with refractory schizophrenia who were using CLZ, and we discuss the implications of this infection on the continuation of CLZ treatment in these patients.

RESULTS

Of these three cases with dengue infection and co-occurence of CLZ use, the first would be classified as severe neutropenia and the second as moderate leucopenia; the last case had a white blood cell (WBC) count inside the normal range, and had no need to change his antipsychotic. The first and the second patient presented a worsening in their schizophrenic psychopathologies, after CLZ withdrawal, evolving into catatonic states, that were reverted after the careful reintroduction of CLZ.

DISCUSSION

It is very likely that during dengue epidemics many patients with schizophrenia and using CLZ have their treatment permanently discontinued given WBC count concerns, causing relapse of symptoms of schizophrenia and impairment of quality of life of these patients.This is the first report of neutropenia cases among CLZ-treated patients during dengue infection that describes the withdrawal of CLZ and its successful readministration.

Successful rechallenge with clozapine following 'red alert'

A case is presented of a 23-year-old lady with treatment-resistant schizoaffective disorder who had responded well to treatment with clozapine. Fifteen months after satisfactory use of clozapine she had 'red alerts' from routine haematological monitoring indicating neutropenia. Clozapine was discontinued and she was admitted to the psychiatric hospital to manage the aftermath of discontinuing clozapine and start alternative treatment with other antipsychotics. Her mental health rapidly deteriorated. Adequate trials with amisulpride, haloperidol, olanzapine and flupenthixol decanoate yielded little improvement in her clinical state. After 9 months of non-response to other antipsychotic medications, she was rechallenged with clozapine, followed by improvement in her mental state. She was eventually discharged home after 14 months of hospitalisation in a stable mental state. She remained mentally stable in the community on clozapine for 18 months after rechallenge, with no further red alerts.

Haematological toxicity of drugs used in psychiatry

Almost all classes of psychotropic agents have been reported to cause blood dyscrasias. Mechanisms include direct toxic effects upon the bone marrow, the formation of antibodies against haematopoietic precursors or involve peripheral destruction of cells. Agranulocytosis is probably the most important drug-related blood dyscrasia. The mortality from drug-induced agranulocytosis is 5-10% in Western countries. The manifestations of agranulocytosis are secondary to infection. Aggressive treatment with intravenous broad-spectrum antimicrobials and bone marrow stimulants may be required. Of drugs encountered in psychiatry, antipsychotics including clozapine (risk of agranulocytosis approximately 0.8%, predominantly in the first year of treatment) and phenothiazines (chlorpromazine agranulocytosis risk approximately 0.13%), and antiepileptics (notably carbamazepine, neutropenia risk approximately 0.5%) are the most common causes of drug-related neutropenia/agranulocytosis. Drugs known to cause neutropenia should not be used concomitantly with other drugs known to cause this problem. High temperature and other indicators of possible infection should be looked for routinely during treatment. Clozapine is well known as a drug that can cause blood dyscrasias, but olanzapine and other atypicals may also cause similar problems. In addition to genetic factors, there are likely to be dose-related and immunological components to these phenomena. Important lessons have been learnt from the haematological monitoring that is necessary with clozapine and the monitoring has been very successful in preventing deaths related to clozapine-induced agranulocytosis. Continuing research into the mechanisms of drug-induced neutropenia and agranulocytosis may serve to further enhance the safe use not only of clozapine, but also of other agents.