Serum Concentrations Of Clozapine Research Articles

Genome-wide association analysis of treatment resistant schizophrenia for variant discovery and polygenic assessment

BackgroundTreatment resistant schizophrenia (TRS) is broadly defined as inadequate response to adequate treatment and is associated with a substantial increase in disease burden. Clozapine is the only approved treatment for TRS, showing superior clinical effect on overall symptomatology compared to other drugs, and is the prototype of atypical antipsychotics. Risperidone, another atypical antipsychotic with a more distinctive dopamine 2 antagonism, is commonly used in treatment of schizophrenia. Here, we conducted a genome-wide association study on patients treated with clozapine (TRS) vs. risperidone (non-TRS) and investigated whether single variants and/or polygenic risk score for schizophrenia are associated with TRS status. We hypothesized that patients who are treated with clozapine and risperidone might exhibit distinct neurobiological phenotypes that match pharmacological profiles of these drugs and can be explained by genetic differences. The study population (n = 1286) was recruited from a routine therapeutic drug monitoring (TDM) service between 2005 and 2022. History of a detectable serum concentration of clozapine and risperidone (without TDM history of clozapine) defined the TRS (n = 478) and non-TRS (n = 808) group, respectively.ResultsWe identified a suggestive association between TRS and a common variant within the LINC00523 gene with a significance just below the genome-wide threshold (rs79229764 C > T, OR = 4.89; p = 1.8 × 10−7). Polygenic risk score for schizophrenia was significantly associated with TRS (OR = 1.4, p = 2.1 × 10−6). In a large post-mortem brain sample from schizophrenia donors (n = 214; CommonMind Consortium), gene expression analysis indicated that the rs79229764 variant allele might be involved in the regulation of GPR88 and PUDP, which plays a role in striatal neurotransmission and intellectual disability, respectively.ConclusionsWe report a suggestive genetic association at the rs79229764 locus with TRS and show that genetic liability for schizophrenia is positively associated with TRS. These results suggest a candidate locus for future follow-up studies to elucidate the molecular underpinnings of TRS. Our findings further demonstrate the value of both single variant and polygenic association analyses for TRS prediction.

Effect of Common Cold on Serum Clozapine Concentrations in Hospitalized Patients with Schizophrenia.

The present study aims to investigate the effect of common cold on the serum clozapine concentrations in hospitalized patients with schizophrenia. A total of 65 schizophrenic patients with common cold receiving clozapine treatment were retrospectively enrolled. The demographic data, medication situation, clozapine concentration, and parameters of routine haematological and biochemical laboratory tests were obtained from the medical record system. The serum clozapine concentration and clozapine concentration/dose (C/D)ratios between the baseline period and cold period were compared by paired-sample t tests. Association between the changes in serum concentration and C/Dratios of clozapine and changes in white blood cell (WBC) and neutrophil (NE) counts was evaluated using Pearson correlation analysis. The serum clozapine concentration (t = -9.856, P < 0.001) and clozapine C/Dratios (t = -10.071, P < 0.001) were found to be significantly elevated in the cold period compared to the baseline period. Moreover, the changes in the serum clozapine concentration were found to be significantly elevated in female patients compared to male patients (t = -2.483, P = 0.017). Furthermore, changes in the serum clozapine concentration were positively correlated to the changes in WBC (r = 0.303, P = 0.014) and NE (r = 0.315, P = 0.011) counts. Similarly, changes in clozapine C/Dratios were positively correlated to the changes in WBC (r = 0.275, P = 0.027) and NE (r = 0.328, P = 0.008) counts. The serum clozapine concentrations in patients with schizophrenia during the common cold period were increased, which might by related to the elevated WBC and NE counts.

Clozapine Dose-Concentration Relationship and Other Factors Associated With Clozapine Plasma Concentration in Korean Schizophrenia Patients

Objectives: Some reports suggest that the concentration-to-dosage ratio (C/D ratio) of clozapine (CZP) in Asian treatment-resistant schizophrenia (TRS) patients differs from that of Caucasian TRS patients. However, there is insufficient research on the differences in C/D ratio between Korean TRS patients and Caucasian TRS patients. Therefore, this study aimed to investigate prescribed CZP dosage, CZP concentration and C/D ratio in Korean TRS patients.Methods: The study included TRS patients aged 18 years or older who were prescribed CZP for at least 12 weeks at a psychiatric hospital in Korea. We collected demographic information, smoking status, hospitalization status, CZP serum concentration, total CZP dosage, and norclozapine (NCZP) serum concentration and analyzed their statistical correlations.Results: The study found that the average daily CZP dosage was 266.1 mg, and the average CZP concentration was 568.0 ng/mL. There was a significant correlation between CZP serum concentration and smoking status, as well as sex. CZP dosage was not significantly associated with age, weight, BMI, or metabolic rate. The study also found a significant difference in C/D ratio between groups based on CZP serum concentration.Conclusion: Our study suggests that recommended CZP dosages for Caucasians may not be suitable for Koreans due to C/D ratio differences. We found a relationship between CZP serum concentration and C/D ratio in Korean TRS patients. Therefore, it is crucial to confirm CZP serum concentration to avoid side effects and to find optimal dosage.

Guía internacional para una dosificación más segura de la clozapina en adultos mediante el uso de 6 titulaciones personalizadas de dosis basados en la etnicidad, la proteína C reactiva y los niveles de clozapina

This is the Spanish translation of an international guideline which proposes improving clozapine package inserts worldwide by using ancestry-based: 1) dosing and 2) titration. Adverse drug reaction (ADR) databases suggest clozapine: 1) is the third most toxic drug in the United States (US), and 2) produces worldwide pneumonia mortality four times greater than that of agranulocytosis or myocarditis. For trough steady-state clozapine serum concentrations, the therapeutic reference range is narrow, from 350 to 600 ng/mL with the potential for toxicity and ADRs as concentrations increase. Clozapine is mainly metabolized by CYP1A2 (female non-smokers require the lowest dose and male smokers the highest dose). Poor metabolizer (PM) status through phenotypic conversion is associated with co-prescription of inhibitors (including oral contraceptives and valproate), obesity or inflammation with C-reactive protein (CRP) elevations. People with ancestry from Asia (Pakistan to Japan) or the Americas’ original inhabitants have lower CYP1A2 activity and require lower clozapine doses to reach concentrations of 350 ng/ml. Daily doses of 300-600 mg/day are recommended in the US. Slow personalized titration may prevent early ADRs (including syncope, myocarditis and pneumonia). The core of this guideline consists of six personalized titration schedules for inpatients: 1) Asian/Amerindian ancestry with lower metabolism (in cases of obesity or valproate) needing minimum therapeutic dosages of 75-150 mg/day, 2) Asian/Amerindian ancestry with average metabolism needing 175-300 mg/day, 3) European/Western Asian ancestry with lower metabolism (in cases of obesity or valproate) needing 100-200 mg/day, 4) European/Western Asian ancestry with average metabolism needing 250-400 mg/day, 5) in the US of non-Asian/Amerindian ancestry with lower clozapine metabolism (in cases of obesity or valproate) needing 150-300 mg/day, and 6) in the US of non-Asian/Amerindian ancestry with average clozapine metabolism needing 300-600 mg/day. Baseline and weekly CRP monitoring for at least 4 weeks is required to identify any inflammation, including inflammation secondary to clozapine rapid titration.

Study on the daily dose and serum concentration of clozapine in psychiatric patients and possible influencing factors of serum concentration

BackgroundClozapine is the most effective drug for treatment-resistant schizophrenia, and the dosage and concentration of clozapine in the treatment of mental illness vary greatly in different populations and are affected by many factors.MethodsThe serum clozapine concentration of 3734 psychiatric patients was detected, and data on daily dose, sex, age and other medical records were collected for statistical analysis.ResultsThe mean daily dose, mean serum concentration and mean C/D (concentration/dose) ratio of clozapine were 191.02 ± 113.47 mg/day, 326.15 ± 235.66 ng/mL and 1.94 ± 1.25 ng/mL per mg/day, respectively. There was difference in daily dose between sexes, and females had higher daily dose (p <0.01), higher serum clozapine concentrations (p < 0.01) and higher C/D ratios (p < 0.01). There were significant differences in daily dose (p < 0.001), serum drug concentration (p < 0.001) and C/D ratio (p < 0.001) among different age groups. The daily dose decreased with age (p for trend < 0.001), and the C/D ratio increased with age (p for trend < 0.001). Inpatients and outpatients had no difference in daily dose, but inpatients had higher serum concentration (p < 0.001) and C/D ratio (p < 0.001). There was no difference in daily dose among different occupations, but there were significant differences in serum concentration (p < 0.001) and C/D ratio (p < 0.001), and unemployed patients may have higher serum concentration and C/D ratio. Duration of disease, comorbidity, marital status, and psychotic type may influence the daily dose and serum concentration.ConclusionsThe effective daily dose and serum concentration of clozapine in the study area may be lower than recommended levels, and women have higher serum concentrations and slower metabolic rates. With increasing age, the daily dose decreases, and the metabolic rate slows. Inpatient status and occupation of patients may influence the serum concentration and metabolic rate of clozapine.

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

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

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

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

Valproate, obesity and other causes of clozapine poor metabolism in the context of rapid titration may explain clozapine-induced myocarditis: A re-analysis of a Turkish case series

IntroductionClozapine-induced myocarditis or any clozapine-induced inflammation may be a hypersensitivity reaction due to titration that was too rapid for the patient's clozapine metabolism. Clozapine metabolism is influenced by ancestry, sex, smoking and the presence of confounders including obesity, infections, and inhibitors (e.g., valproate) causing the patient to behave as a clozapine poor metabolizer (PM). A published study in a Turkish hospital identified 1 case of clozapine-induced pancreatitis and hepatitis and 9 cases of clozapine-induced myocarditis. To explore the hypothesis that the 10 patients were clozapine PMs, their serum clozapine concentrations were investigated using concentration-to-dose (C/D) ratios and their titrations carefully reviewed. MethodsDividing the trough serum concentration by the dose produces the clozapine C/D ratio. The dose required to reach 350ng/ml was considered the minimum therapeutic dosage and was used to classify patients according to clozapine PM status. Titration speed was assessed. ResultsAll 10 patients were possibly clozapine PMs (3 of them had as minimum therapeutic doses: 72, 82 or 83mg/day). Nine of the 10 patients may have behaved as clozapine PMs due to obesity and/or valproate co-prescription during titration. One also had an undiagnosed infection. Of the 10 patients, 9 had at least 1 of 3 factors: too-rapid titration in the first or second weeks, or a final dosage that was too high. ConclusionsFuture studies using clozapine levels and considering the role of clozapine PM status should explore whether or not all cases of clozapine-induced inflammation could be explained by lack of individualized titration.

Case Report: The Challenges of Assessing and Managing Dysphagia in Two Patients on Long-term Clozapine

<h3>Introduction</h3> Introduction: The risk of clozapine associated dysphagia is between 1/1000 and 1/10000 (1). The associated complications of aspiration, pneumonia and mortality are also observed to be elevated with clozapine use(2). There is also limited evidence suggesting that risk is dose and age dependent (2), We present two cases illustrating the potential complex presentations of dysphagia in patients on clozapine. <h3>Methods</h3> Methods: The first case is a 61-year-old male veteran with history of chronic schizophrenia admitted for worsening psychosis. He has been on clozapine up to 550mg since 2001, with clozapine/norclozapine levels at 452/232. Exam was remarkable for an AIMS score of 25. During admission patient reported odynophagia, dysphagia and a 40-pound weight loss. Initial workup revealed candida esophagitis. 21-day course of fluconazole yielded no improvement. Inpatient team did not increase dose due to concern for esophageal dysmotility. Manometry is pending at the writing of this case report, hydroxyzine was reduced and benztropine discontinued to reduce anticholinergic burden. The second patient was a 51-year-old female with history of schizoaffective disorder, chronic PTSD, alcohol use disorder, bulimia nervosa, temporal lobe epilepsy, iron deficiency anemia, and GERD. Patient was on clozapine from 2009 until 2016. In 2015, she reported dysphagia worsening for one year with solid food dysphagia, choking, and sialorrhea. Subsequent manometry revealed type II achalasia and clozapine was discontinued within one year and switched to aripiprazole and eventually olanzapine. Over subsequent years, patient's dysphagia worsened and led to severe malnutrition. In 2020, she underwent Heller's myotomy with Dor fundoplication, with the expectation that dysphagia may remain given multifactorial etiology including polypharmacy. Patient also received a PEG tube. In 2020-2021, patient had more than 20 admissions for recurrent aspiration pneumonitis. In July 2021, she was admitted for replacement of a PEG tube and patient went into pulseless electrical arrest. Aspiration was cited as a factor in her death. <h3>Results</h3> Discussion: Dysphagia with antipsychotics can be mediated by multiple mechanisms including parkinsonism, acute dystonic reactions, tardive dyskinesia, sialorrhea, xerostomia, and sedation. Management approaches include reduction of clozapine and switching to another antipsychotic although these interventions may not reduce dysphagia. Aspiration on clozapine leads to a release of cytokines which can increase serum concentration of clozapine and in turn, side-effects (3). <h3>Conclusions</h3> Conclusion: These two cases illustrate the challenges in assessing and managing dysphagia in patients on clozapine. In both cases, dysphagia became an issue years after initiation of clozapine. In the first case, the veteran's dysphagia was likely mediated by tardive dyskinesia and oversedation. In the second case, dysphagia was likely mediated by sialorrhea, oversedation and other multiple comorbidities. More systematic studies are needed to better characterize risk of clozapine associated dysphagia and treatment approaches. <h3>This research was funded by</h3> none

First Use of Clozapine Point of Care Testing in Acute Inpatient Psychiatry: Preliminary Report.

Clozapine is the antipsychotic of choice in treatment-resistant schizophrenia. Serum clozapine concentration testing is essential to monitor adherence, adjust dosing, and ensure treatment safety. However, patients who are acutely unwell are frequently reluctant to undergo blood testing requiring venipuncture. Also, conventional laboratory-based measurement of clozapine plasma levels can take days, thus contributing to the suboptimal use of clozapine when it is most needed. We pioneered clozapine whole-blood point of care (POC) testing in the acute inpatient setting in the treatment of a group of actively psychotic patients receiving clozapine during the outbreak of the COVID-19 pandemic. POC clozapine testing using automated homogenous immunoassay requires only finger prick blood sampling and is more acceptable to patients. As it produces results in minutes, clozapine POC testing serves to promptly ascertain adherence with treatment and inform therapeutic dosing. POC testing offered a more practical, less invasive, and quicker alternative to conventional methods of monitoring clozapine levels. Near immediate availability of clozapine levels expedited clinical decisions and helped ensure safe clozapine prescribing to our severely psychotic patients in a time of crisis. By facilitating patients' early safe discharge from the hospital, clozapine POC testing also reduced length of hospitalization.

An International Adult Guideline for Making Clozapine Titration Safer by Using Six Ancestry-Based Personalized Dosing Titrations, CRP, and Clozapine Levels.

This international guideline proposes improving clozapine package inserts worldwide by using ancestry-based dosing and titration. Adverse drug reaction (ADR) databases suggest that clozapine is the third most toxic drug in the United States (US), and it produces four times higher worldwide pneumonia mortality than that by agranulocytosis or myocarditis. For trough steady-state clozapine serum concentrations, the therapeutic reference range is narrow, from 350 to 600 ng/mL with the potential for toxicity and ADRs as concentrations increase. Clozapine is mainly metabolized by CYP1A2 (female non-smokers, the lowest dose; male smokers, the highest dose). Poor metabolizer status through phenotypic conversion is associated with co-prescription of inhibitors (including oral contraceptives and valproate), obesity, or inflammation with C-reactive protein (CRP) elevations. The Asian population (Pakistan to Japan) or the Americas' original inhabitants have lower CYP1A2 activity and require lower clozapine doses to reach concentrations of 350 ng/mL. In the US, daily doses of 300-600 mg/day are recommended. Slow personalized titration may prevent early ADRs (including syncope, myocarditis, and pneumonia). This guideline defines six personalized titration schedules for inpatients: 1) ancestry from Asia or the original people from the Americas with lower metabolism (obesity or valproate) needing minimum therapeutic dosages of 75-150 mg/day, 2) ancestry from Asia or the original people from the Americas with average metabolism needing 175-300 mg/day, 3) European/Western Asian ancestry with lower metabolism (obesity or valproate) needing 100-200 mg/day, 4) European/Western Asian ancestry with average metabolism needing 250-400 mg/day, 5) in the US with ancestries other than from Asia or the original people from the Americas with lower clozapine metabolism (obesity or valproate) needing 150-300 mg/day, and 6) in the US with ancestries other than from Asia or the original people from the Americas with average clozapine metabolism needing 300-600 mg/day. Baseline and weekly CRP monitoring for at least four weeks is required to identify any inflammation, including inflammation secondary to clozapine rapid titration.

Pharmacogenetic excitation of the median raphe region affects social and depressive-like behavior and core body temperature in male mice

AimsMedian raphe region (MRR) is an important bottom-up regulatory center for various behaviors as well as vegetative functions, but detailed descriptions and links between the two are still largely unexplored. MethodsPharmacogenetics was used to study the role of MRR in social (sociability, social interaction, resident intruder test) and emotional behavior (forced swim test) parallel with some vegetative changes (biotelemetry: core body temperature). Additionally, to validate pharmacogenetics, the effect of clozapine-N-oxide (CNO), the ligand of the artificial receptor, was studied by measuring (i) serum and brainstem concentrations of CNO and clozapine; (ii) MRR stimulation induced neurotransmitter release in hippocampus; (iii) CNO induced changes in body temperature and locomotor activity. Key findingsMRR stimulation decreased locomotion, increased friendly social behavior in the resident intruder test and enhanced depressive-like behavior. The latter was accompanied by diminished decrease in core body temperature. Thirty minutes after CNO injection clozapine was predominant in the brainstem. Nonetheless, peripheral CNO injection was able to induce glutamate release in the hippocampus. CNO had no immediate (<30 min) or chronic (repeated injections) effect on the body temperature or locomotion. SignificanceWe confirmed the role of MRR in locomotion, social and depressive-like behavior. Most interestingly, only depressive-like behavior was accompanied by changed body temperature regulation, which was also observed in human depressive disorders previously. This indicates clinical relevance of our findings. Despite low penetration, CNO acts centrally, but does not influence the examined basic parameters, being suitable for repeated behavioral testing.

Absolute and Dose-Adjusted Serum Concentrations of Clozapine in Patients Switching vs. Maintaining Treatment: An Observational Study of 1979 Patients.

BackgroundClozapine is an effective drug for the management of schizophrenia that has not responded to other agents, but some patients experience insufficient or adverse effects and discontinue treatment.ObjectiveWe investigated a potential association between clozapine serum concentrations and switching to other antipsychotics in a large real-world patient population from a therapeutic drug monitoring service.MethodsAbsolute and dose-adjusted serum concentrations (concentration-to-dose ratios [C/D ratios]) of clozapine during dosing between 100 and 1000 mg/day were measured in 1979 Norwegian patients during the period 2005–2019. These variables were compared in patients switching to other antipsychotic drugs versus maintaining clozapine treatment using linear mixed models. Smoking habits were known for 49% of the patients. To prevent potential nonadherence affecting clozapine switching, only patients with serum concentrations above 50% of the lower reference range were included.ResultsIn total, 190 patients (9.6%) switched from clozapine to another antipsychotic drug during the study period, whereas the remaining patients were not detected as switchers and were interpreted as maintaining treatment. Patients switching treatment had 23.5% lower absolute concentrations (954 vs. 1245 nmol/L; p < 0.001) and 15.7% lower daily doses (305 vs. 362 mg/day; p < 0.001) of clozapine than did nonswitchers, making the clozapine C/D ratio 9.7% lower in switchers than in nonswitchers after correcting for smoking habits (2.80 vs. 3.10 nmol/L/mg/day; p = 0.032).ConclusionsThe present study suggests that decreased absolute and dose-adjusted serum concentrations of clozapine were associated with clozapine discontinuation. The significantly reduced clozapine concentrations regardless of prescribed dose in switchers versus nonswitchers may indicate a pharmacokinetic mechanism underlying the risk of clozapine discontinuation.

Clozapine intoxication with severe adverse effects induced by an inflammatory and infectious process: a case report

BackgroundClozapine intoxication can be life-threatening. Outside of the common drug–drug interactions, tobacco smoking, and caffeine consumption, infectious and inflammatory processes are important contributors to clozapine intoxication. Although this relationship has been reported previously, the literature is scant of proper research articles describing the presentation and management of this unpredictable interaction. Therefore, clinicians need to rely heavily on case reports describing clozapine intoxication caused by inflammation and/or infection.Case presentationA 64-year-old Caucasian woman known for schizophrenia was brought to the emergency department (ED) with severe signs and symptoms of clozapine intoxication (general deterioration, drowsiness, neutropenia, and ileus). She was on clozapine 700 mg daily amongst other medications. The clozapine dose was stable for over 3 years, and there were no recent changes in her medications. The initial culprit was determined to be an infectious/inflammatory process of gastrointestinal origin with contribution from dehydration and constipation. Clozapine and norclozapine serum concentrations confirmed the intoxication: 1315 ng/mL and 653 ng/mL, respectively. She drastically improved with clozapine dose reduction and antibiotic therapy. She remained stable for years with clozapine 600 mg daily with stable clozapine serum levels.ConclusionThis case report illustrates the possibility of severe toxicity associated with an acute infectious and/or inflammatory process in patients on clozapine therapy. Clinicians must maintain a high level of suspicion in patients taking clozapine who develop and an infectious and/or inflammatory process. Constipation secondary to clozapine intoxication can exacerbate the initial intoxication process.

Impact of Body Mass Index on Serum Concentrations of Antidepressants and Antipsychotics.

Rates of overweight and obesity are higher in patients suffering from psychiatric disorders than in the general population. Body composition and enzyme functions are affected by overweight, and consequently, the pharmacokinetics of drugs may vary in overweight patients. Thus, overweight and obesity are important factors in psychiatric disorders and their treatment. This analysis aimed to investigate the impact of body mass index (BMI) on serum concentrations of the antidepressant drugs amitriptyline, doxepin, escitalopram, mirtazapine, and venlafaxine, and the antipsychotic drugs clozapine, quetiapine, and risperidone, taking into account the following confounding parameters: age, sex, and smoking habit. Inpatients and outpatients (N = 1657) who took at least one of the target drugs were included in this retrospective analysis. Serum concentrations of the target drugs and their metabolites were determined at the Department of Psychiatry, Psychosomatics, and Psychotherapy of the University Hospital of Würzburg during routine therapeutic drug monitoring (January 2009-December 2010), which was performed in the morning (trough level) at steady state. Dose-corrected serum concentrations (CD) of the active moiety of doxepin and venlafaxine and of O-desmethylvenlafaxine were negatively associated with BMI (partial Pearson correlation, R = -0.267, P = 0.002; R = -0.206, P ≤ 0.001; R = -0.258, P ≤ 0.001), and the CDs were different in normal weight, overweight, and obese patients (analysis of covariance, P = 0.004, P < 0.001, P ≤ 0.001). No association was found between BMI and serum concentrations of amitriptyline, escitalopram, mirtazapine, clozapine, quetiapine, and risperidone. In obese patients, higher doses of doxepin and venlafaxine are necessary to achieve similar serum concentrations as in normal weight patients and to avoid treatment-resistant depression.

Association Between N-Desmethylclozapine and Clozapine-Induced Sialorrhea: Involvement of Increased Nocturnal Salivary Secretion via Muscarinic Receptors by N-Desmethylclozapine.

Clozapine-induced sialorrhea (CIS) is a common side effect of clozapine. There is no established standard treatment of CIS since the underlying mechanism remains unknown. This study aimed to elucidate the mechanisms involved in CIS. In our clinical study, a prospective observational study evaluated the association between serum and saliva concentrations of clozapine or its metabolites and Drooling Severity and Frequency Scale (DSFS) score. In our in vivo study, we first developed a new CIS animal model; subsequently, we measured salivary secretion and concentrations of clozapine or its metabolites in the animal model. In our in vitro study, we measured the calcium ion (Ca2+) response to evaluate the effect of clozapine or its metabolites on human salivary gland cell line (HSY cells) and then examined whether their effect was inhibited by atropine. In our clinical study, serum and saliva N-desmethylclozapine concentrations were significantly correlated with nocturnal DSFS score. In our in vivo study, daily single oral administration of 100 mg/kg clozapine for 7 days significantly increased salivary secretion in rats. Furthermore, N-desmethylclozapine concentrations in serum and submandibular glands of the rats were higher than clozapine concentrations. In our in vitro study, N-desmethylclozapine only elicited an increase in the intracellular Ca2+ in HSY cells. N-desmethylclozapine-induced Ca2+ responses were inhibited by atropine. These results suggest that N-desmethylclozapine is implicated in CIS by increasing nocturnal salivation via the muscarinic receptors. Moreover, our developed animal model that reflects CIS in clinical condition plays a key role as a bridge between basic and clinical research. SIGNIFICANCE STATEMENT: Clozapine-induced sialorrhea (CIS) is a severe and frequent adverse reaction, but the mechanism underlying CIS is less well understood. This paper reports that N-desmethylclozapine, a metabolite of clozapine, is implicated in CIS by increasing nocturnal salivation via the muscarinic receptors and that oral administration of clozapine at 100 mg/kg once daily for 7 days to rat is the optimum method for establishing the new animal model reflecting the clinical scenario of CIS.

The relationship between serum clozapine concentrations and hematological parameters by a validated mass spectrometric method

ObjectiveClozapine is one of the most effective drugs for resistant schizophrenia, but its severe metabolic and hematological side effects limit the use of clozapine. It has been reported that clozapine blood concentrations should be maintained between 350−600 ng/mL. Our aim was to develop a determination method for clozapine and its main metabolites norclozapine and clozapine-N-oxide, to perform validation studies and to investigate the change of various biochemical parameters in patients using clozapine. MethodsA liquid chromatography-tandem mass spectrometry (LC–MS/MS) method was developed and validated for clozapine measurement. Thus, blood samples were collected from 38 patients with schizophrenia and 32 healthy volunteers. Biochemical and hematological parameters were measured by Beckman-Coulter AU 5800 (Beckman Coulter, Brea, USA) and Beckman Coulter LH 780 analyzer (Beckman Coulter, Miami, FL, USA), respectively. Hormone levels were analyzed using Cobas 6000 analyzer (Roche Diagnostics, Germany). ResultsThe LCMS/MS method was linear between 1.22−2500 ng/mL (r2 = 0.9971) for clozapine. The retention times of clozapine, norclozapine and clozapine-N-oxide were 0.92, 0.89 and 0.95, respectively. Blood glucose (GLU) (p = 0.025), low density lipoprotein (LDL-cholesterol) (p = 0.015), triglyseride (TG) (p = 0.042) and total cholesterol (TC) (p = 0.024) levels were higher; hemoglobin (HGB) (0.015), mean corpuscular hemoglobin (MCH) (0.036), red blood cell count (RBC) (0.020), neutrophil (NEU) (0.034), and platelet (PLT) (P = 0.005) levels were lower in the clozapine group. ConclusionsThis LC–MS/MS method was rapid, simple, cost-effective and suitable for the routine clozapine monitoring. Furthermore, norclozapine and clozapine-N-oxide were also determined. Monitoring of metabolic and hematological parameters with clozapine levels is very important. However, the limitations of the study were that the method was not validated for norclozapine and clozapine-N-oxide, so the validation parameters were not evaluated for these two metabolites.

Caracterización in silico de la farmacocinética de clozapina en distintas poblaciones de pacientes.

La clozapina es un fármaco antipsicótico atípico de estrecho margen terapéutico (0,35 mg/L – 0,60 mg/L) y con riesgo de reacciones adversas poco frecuentes, pero de gran riesgo, por lo que es necesaria su monitorización. Con el avance del diseño de aplicaciones y programas informáticos se pueden realizar simulaciones farmacocinéticas de distintas moléculas para estimar su comportamiento en el cuerpo humano. Este estudio tiene como objetivo realizar diversas simulaciones in silico modificando parámetros de aclaramiento según la edad, el sexo o el hábito tabáquico, comparando los resultados obtenidos con ensayos poblacionales. SymCYP® v16.1 es un software informático que posee librerías de datos fisicoquímicos sobre diversos sustratos y datos poblaciones que, junto a los datos farmacocinéticos obtenidos de la revisión bibliográfica realizada, permiten la simulación de curvas farmacocinéticas y parámetros farmacocinéticos de clozapina en una población determinada. Los resultados obtenidos ponen de manifiesto diferencias significativas en las concentraciones séricas de clozapina en función del sexo y de la edad, siendo necesarios ajustes de dosis para mantener concentraciones dentro de niveles seguros. En conclusión, este trabajo ofrece una nueva visión al desarrollo de nuevas moléculas gracias a la utilización de simulaciones in silico masivas.

Effect of fluvoxamine augmentation and smoking on clozapine serum concentrations

BackgroundClozapine (CLZ) is metabolized via cytochrome P450 CYP1A2 to N-desmethylclozapine (NCLZ). Smoking induces CYP1A2 thereby increasing clozapine metabolism whereas fluvoxamine inhibits CYP1A2. Studies suggest that the beneficial effect of fluvoxamine augmentation in raising serum clozapine concentrations also occurs when serum concentrations are low due to smoking. Yet, little is known about the influence of fluvoxamine augmentation on clozapine serum concentrations in smoking versus non-smoking patients. MethodsA TDM database was analyzed. Serum concentrations of CLZ, NCLZ, dose-adjusted serum concentrations (C/D) and metabolite-to-parent ratios (MPR) were compared using non-parametrical tests in four groups: clozapine-monotherapy in non-smokers (VNS, n = 28) and smokers (VS, n = 43); combined treatment with clozapine and fluvoxamine in non-smokers (VNS+F, n = 11) and smokers (VS+F, n = 43). ResultsThe CLZ monotherapy smoking group showed lower values of C/D CLZ of −38.6% (p < 0.001), C/D NCLZ −35.6% (p < 0.001) and a higher MPR (p = 0.021) than in the non-smoking group. The combination of CLZ and fluvoxamine in non-smoking patients led to higher C/D values: C/D CLZ +117.9% (p < 0.001), C/D NCLZ +60.8% (p = 0.029) while the MPR did not differ between groups (p = 0.089). Changes were comparable to fluvoxamine augmentation in the smoking group with increased C/D CLZ of +120.1% (p < 0.001), C/D NCLZ of +85.8% (p < 0.001) and lower MPR (p = 0.006). ConclusionsSmoking in clozapine monotherapy reduced median dose-adjusted serum concentrations more than a third. Combined treatment with fluvoxamine and clozapine led to higher median C/D values in both, smokers and non-smokers. The opposing effects of CYP1A2 induction by smoking and inhibition by fluvoxamine on clozapine serum concentrations balanced out.

Relationship between Clozapine-Induced Electroencephalogram Abnormalities and Serum Concentration of Clozapine in Japanese Patients with Treatment-Resistant Schizophrenia.

Objective The objective of this study was to investigate the relationship between the serum concentration of clozapine (C-CLZ), Ndesmethylclozapine (N-CLZ) and the daily dose of CLZ (D-CLZ), and the relationships among CLZ and electroencephalogram (EEG) abnormalities. Methods Twenty-eight patients were recruited to this study, but 8 patients were excluded because clozapine was discontinued before the post-treatment measurement of EEG or C-CLZ. Ultimately, 20 patients (6 men, 14 women) with an average age of 36 years were enrolled. The subjects were divided into EEG normal and abnormal groups. C-CLZ and N-CLZ were measured at 4, 12, 26, and 52 weeks after initiating CLZ administration. Results All patients had normal baseline EEG signals, and 8 patients showed EEG abnormalities later. There were significant correlations between C-CLZ and D-CLZ, and between N-CLZ and D-CLZ. The C-CLZ/D-CLZ, N-CLZ/D-CLZ, and C-CLZ/N-CLZ ratio were not significantly different between the EEG normal and EEG abnormal groups. The EEG abnormal group had significant higher proportion of patients with high intra-individual variability in their C-CLZ/D-CLZ ratio. Conclusion There is no relationship between C-CLZ and EEG abnormalities. However, patients with high intra-individual variability in their C-CLZ/D-CLZ ratio had greater possibility of exhibiting EEG abnormalities.