Factors predicting serum clozapine levels in Middle Eastern patients

Objectives: Despite its superiority over other drugs for psychosis, clozapine remains underused and is associated with many clinical challenges, including difficulties in predicting serum levels. We thus investigated the clinical predictors of clozapine serum levels in Middle Eastern patients. Methods: This was a cross-sectional study including 94 patients of Middle Eastern ethnicity. Results: The average clozapine dose and serum level were 400 mg/daily and 705 ng/mL, respectively. Clozapine dose and serum levels were positively correlated (rs [94]=0.32, p=0.002). A predictive model of serum clozapine levels revealed that the daily dose, smoking status, use of fluvoxamine or lamotrigine, and body mass index predicted 43.6% of the variance in serum levels (p<0.001). Using this model, the maximum doses of clozapine to avoid levels above the optimal range (>650 ng/mL) were 300, 250, or 225 mg/day for non-smokers with a body mass index of 25, 30, or 35 kg/m2, respectively, and 475, 425, or 400 mg/day for smokers with a body mass index of 25, 30, or 35 kg/m2, respectively. Conclusions: These findings do not reduce the value of individualised therapeutic drug monitoring but may assist clinicians when prescribing clozapine to Middle Eastern patients. Further psychopharmacological studies are needed on this demographic population.

Predictors of laxative use in inpatients with schizophrenia on clozapine

Objectives: Constipation, a clinical manifestation of gastrointestinal hypomotility, is a common and potentially serious complication of clozapine therapy, requiring laxatives for its prevention and treatment. We explored the predictive factors of the increased laxative use in inpatients receiving a long-term clozapine therapy. Methods: In the cross-sectional study of 93 patients in a psychiatric rehabilitation hospital, we examined a four-week prevalence of laxative use and a range of demographic and clinical factors associated with the number of prescribed laxatives. Results: Seventy-four percent of inpatients with schizophrenia were prescribed laxatives, and they were statistically significant older and taking higher daily doses of clozapine. In generalized Poisson regression analysis, the clozapine dose, age, and comorbid diabetes mellitus and hypothyroidism were independently associated with the number of concurrently used laxatives. No association was found between the laxatives and gender, duration of clozapine treatment, and the number of other medications with a potential to cause constipation. Conclusion: The clozapine dose, age, diabetes mellitus, and hypothyroidism were shown to be the independent predictors of the increased laxative use among inpatients on clozapine and might be associated with the increased risk of clozapine-induced constipation and gastrointestinal hypomotility.

Audit on clozapine dose and plasma level correlation for patients with chronic treatment-resistant psychosis

AimsClozapine is associated with a risk of severe adverse events for which there are current monitoring systems are in place; however, there are no established regimens for monitoring of clozapine plasma levels. Recent Medicines and Healthcare products Regulatory Agency (MHRA) guidance advises clozapine levels should be monitored in certain clinical situations where toxicity may be suspected. This audit aimed to evaluate current practice of clozapine level monitoring within one Local Mental Health Team (LMHT).MethodElectronic (RiO) records of 41 patients (33 male, 8 female; aged from 27 to 76 years; mean age 45 years) registered to the ZTAS system within the Nottingham City Central LMHT were reviewed. 46% had been on clozapine for over 16 years. 73.3% of patients were within clusters 12 and 13; 25.4% of patients were in cluster 11, with one patient in cluster 8. Dates of clozapine plasma level tests for each patient between 2006 and 2020 were found on the electronic NoTIS system, along with clozapine, norclozapine and total clozapine levels. Concurrent clozapine dose and regimens were obtained from pharmacy records from 2018 onwards.Result273 clozapine plasma levels were conducted between 2006 and 2020. The average interval between levels taken was 10 months, 2 weeks but had a wide range, the shortest interval being 2 days, the longest being 13 years. 88 levels taken were >600 ug/L, suggesting increased toxicity risk. 108 levels were <350 ug/L, suggesting possible sub-optimal dosing or non-compliance. Statistical tests on correlation coefficient, although statistically non-significant (R = 0.37), showed a positive trend between total clozapine dose and the plasma level between all 3 parameters (i.e. clozapine, norclozapine and total clozapine).ConclusionThere does not appear to be any routine plasma clozapine level monitoring throughout the LMHT with an average interval between tests of 10 months. There was a non-significant but positive trend between total daily dose of clozapine and clozapine level. 32% of clozapine levels returned were higher than the recommended level. We would recommend as suggested in the guidelines from MHRA, clozapine plasma levels should be monitored in certain clinical situations with increased toxicity risk. Trough levels should be taken with records of time of previous dose taken. Limitations of this study included a small sample size (41 patients) with data collection reliant on electronic systems. It was unclear if these results represent trough levels, making values difficult to interpret. Multifactorial impact on clozapine metabolism causes wide patient variability in plasma levels.

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

Background Clozapine 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 presentation A 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. Conclusion This 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.

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

Background: There have been scarce data on the distribution of clozapine concentrations in comparison with the recommended range (350–600 ng/ml) or their relationship with side effects among patients with treatment-resistant schizophrenia. Furthermore, no studies have assessed the association between side effects and overall exposure to the drug by calculating the 24-h area-under-curve (AUC). Methods: In- and outpatients with schizophrenia or schizoaffective disorder (ICD-10) who were receiving a stable dose of clozapine for ⩾2 weeks were included. Side effects were assessed using the Glasgow antipsychotic side-effects scale for clozapine (GASS-C). Using two collected plasma samples, plasma clozapine and norclozapine concentrations at peak and trough and their 24-h AUC were estimated using population pharmacokinetic models. Results: A total of 108 patients completed the study (mean ± SD age, 43.0 ± 10.1 years; clozapine dose, 357.5 ± 136.9 mg/day); 33 patients (30.6%) showed estimated trough concentrations of clozapine within the recommended range (350–600 ng/ml) whereas the concentrations were higher and lower than this range among 37 (43.5%) and 28 (25.9%) patients (%), respectively. There were no significant correlations between estimated peak or trough concentrations or 24-h AUC of both clozapine or norclozapine, and GASS-C total or individual scores. No significant differences were found between GASS-C total or individual item scores between the patients with estimated trough concentrations of clozapine of >600 ng/ml and the other subjects. Conclusion: The results suggest that clozapine or norclozapine concentrations are not linked directly to the extent of side effects experienced in clozapine-treated patients with treatment-resistant schizophrenia while the cross-sectional study design limits the interpretation of any causal relationships. These findings indicate that side effects associated with clozapine may occur at any dose or concentration.

Clozapine: An Updated Overview of Pharmacogenetic Biomarkers, Risks, and Safety—Particularities in the Context of COVID-19

Background: clozapine (CLZ) use is precarious due to its neurological, cardiovascular, and hematological side effects; however, it is the gold standard in therapy-resistant schizophrenia (TRS) in adults and is underused. Objective: to examine the most recent CLZ data on (a) side effects concerning (b) recent pharmacological mechanisms, (c) therapy benefits, and (d) the particularities of the COVID-19 pandemic. Data sources: a search was performed in two databases (PubMed and Web of Science) using the specific keywords “clozapine” and “schizophrenia”, “side effects”, “agranulocytosis”, “TRS”, or “bipolar affective disorder (BAF)” for the last ten years. Study eligibility criteria: clinical trials on adults with acute symptoms of schizophrenia or related disorders. Results: we selected 37 studies, randomized controlled trials (RCTs), and clinical case series (CCS), centered on six main topics in the search area: (a) CLZ in schizophrenia, (b) CLZ in bipolar disorder, (c) side effects during the clozapine therapy, (d) CLZ in pregnancy, (e) CLZ in early-onset schizophrenia, and (f) CLZ therapy and COVID-19 infection. Limitations: we considered RCTs and CCS from two databases, limited to the search topics. Conclusions and implications of key findings: (a) clozapine doses should be personalized for each patient based on pharmacogenetics testing when available; the genetic vulnerability postulates predictors of adverse reactions’ severity; patients with a lower genetic risk could have less frequent hematological monitoring; (b) a CLZ-associated risk of pulmonary embolism imposes prophylactic measures for venous thromboembolism; (c) convulsive episodes are not an indication for stopping treatment; the plasma concentration of clozapine is a better side effect predictor than the dosage; (d) COVID-19 infection may enhance clozapine toxicity, generating an increased risk of pneumonia. Therapy must be continued with the proper monitoring of the white blood count, and the clozapine dose decreased by half until three days after the fever breaks; psychiatrists and healthcare providers must act together.

Clozapine: An Updated Overview of Pharmacogenetic Biomarkers, Risks, and Safety—Particularities in the Context of COVID-19

Background: Clozapine (CLZ) use is precarious due to its neurological, cardiovascular, and hematological side effects; however, it is the gold standard in therapy-resistant schizophrenia (TRS) in adults and is underused. Objective: to examine the most recent CLZ data on (a) side effects concerning (b) recent pharmacological mechanisms, (c) therapy benefits, and (d) the particularities of the COVID-19 pandemic. Data sources: a search was performed in two databases (PubMed and Web of Science) using the specific keywords "clozapine" and "schizophrenia," "side effects," "agranulocytosis," "TRS," or "bipolar affective disorder (BAF)" for the last ten years. Study eligibility criteria: clinical trials on adults with acute symptoms of schizophrenia or related disorders. Results: We selected 37 studies, randomized controlled trials (RCTs), and clinical case series (CCS), centered on six main topics in the search area: (a) CLZ in schizophrenia, (b) CLZ in bipolar disorder, (c) side effects during the clozapine therapy, (d) CLZ in pregnancy, (e) CLZ in early-onset schizophrenia, and (f) CLZ therapy and COVID-19 infection. Limitations: We considered RCTs and CCS from two databases, limited to the search topics. Conclusions and implications of key findings: (a) Clozapine doses should be personalized for each patient based on pharmacogenetics testing when available; the genetic vulnerability postulates predictors of adverse reactions' severity; patients with a lower genetic risk could have less frequent hematological monitoring; (b) CLZ-associated risk of pulmonary embolism imposes prophylactic measures for venous thromboembolism; (c) convulsive episodes are not an indication for stopping treatment; the plasma concentration of clozapine is a better side effect predictor than the dosage; (d) COVID-19 infection may enhance clozapine toxicity, generating an increased risk of pneumonia. Therapy must be continued with proper monitoring of the white blood count, and the clozapine dose decreased by half until three days after the fever breaks; psychiatrists and healthcare providers must act together. Background: Clozapine (CLZ) use is precarious due to its neurological, cardiovascular, and hematological side effects; however, it is the gold standard in therapy-resistant schizophrenia (TRS) in adults and is underused. Objective: to examine the most recent CLZ data on (a) side effects concerning (b) recent pharmacological mechanisms, (c) therapy benefits, and (d) the particularities of the COVID-19 pandemic. Data sources: a search was performed in two databases (PubMed and Web of Science) using the specific keywords "clozapine" and "schizophrenia," "side effects," "agranulocytosis," "TRS," or "bipolar affective disorder (BAF)" for the last ten years. Study eligibility criteria: clinical trials on adults with acute symptoms of schizophrenia or related disorders. Results: We selected 37 studies, randomized controlled trials (RCTs), and clinical case series (CCS), centered on six main topics in the search area: (a) CLZ in schizophrenia, (b) CLZ in bipolar disorder, (c) side effects during the clozapine therapy, (d) CLZ in pregnancy, (e) CLZ in early-onset schizophrenia, and (f) CLZ therapy and COVID-19 infection. Limitations: We considered RCTs and CCS from two databases, limited to the search topics. Conclusions and implications of key findings: (a) Clozapine doses should be personalized for each patient based on pharmacogenetics testing when available; the genetic vulnerability postulates predictors of adverse reactions' severity; patients with a lower genetic risk could have less frequent hematological monitoring; (b) CLZ-associated risk of pulmonary embolism imposes prophylactic measures for venous thromboembolism; (c) convulsive episodes are not an indication for stopping treatment; the plasma concentration of clozapine is a better side effect predictor than the dosage; (d) COVID-19 infection may enhance clozapine toxicity, generating an increased risk of pneumonia. Therapy must be continued with proper monitoring of the white blood count, and the clozapine dose decreased by half until three days after the fever breaks; psychiatrists and healthcare providers must act together.