Drug interactions affecting clozapine levels

Characteristics and causes of reported clozapine-related medication errors: analysis of the Ministry of Health database in Saudi Arabia

BACKGROUND

Clozapine has shown great efficacy in treating treatment-resistant schizophrenia, but it is associated with a variety of medication- related safety problems. Despite this, there remains a lack of research on medication errors (MEs) associated with its use.

AIM

To characterize the nature and contributory factors of clozapine-related MEs reported from government hospitals and primary care centres in Saudi Arabia (SA).

METHOD

A cross-sectional analysis was carried out on MEs related to clozapine use reported to the General Administration of Pharmaceutical Care at the Ministry of Health (MOH) in Saudi Arabia between 2018 and 2022. The data were analysed descriptively to examine the nature and contributory factors of MEs.

RESULTS

A total of 1,165 MEs were reported. The majority of reported errors involved patients aged > 18 years old, with 72.2% (n = 841) being male. The central region was found to report errors more frequently (32.3%, n = 376). Pharmacists were reported to detect errors most frequently (59.6%, n = 695). MEs most often occurred in the prescribing stage (77.8%, n = 906), with "missing prescription information" (30.1%, n = 351) being the most frequent finding. The most frequent contributing factor was the lack of policy (33.1%, n = 351). The majority of errors did not reach the patients (92.3%, n = 1,075), and those that did reach patients rarely resulted in harm (0.3%, n = 2).

CONCLUSION

This study identified areas for improvement which could expedite the development of remedial interventions to reduce the risk of errors.

Overcoming the barriers to identifying and managing treatment-resistant schizophrenia and to improving access to clozapine: A narrative review and recommendation for clinical practice

Clozapine is the only approved antipsychotic for treatment-resistant schizophrenia (TRS). Although a large body of evidence supports its efficacy and favorable risk-benefit ratio in individuals who have failed two or more antipsychotics, clozapine remains underused. However, variations in clozapine utilization across geographic and clinical settings suggest that it could be possible to improve its use. In this narrative review and expert opinion, we summarized information available in the literature on the mechanisms of action, effectiveness, and potential adverse events of clozapine. We identified barriers leading to discouragement in clozapine prescription internationally, and we proposed practical solutions to overcome each barrier. One of the main obstacles identified to the use of clozapine is the lack of appropriate training for physicians: we highlighted the need to develop specific professional programs to train clinicians, both practicing and in residency, on the relevance and efficacy of clozapine in TRS treatment, initiation, maintenance, and management of potential adverse events. This approach would facilitate physicians to identify eligible patients and offer clozapine as a treatment option in the early stage of the disease. We also noted that increasing awareness of the benefits of clozapine among healthcare professionals, people with TRS, and their caregivers can help promote the use of clozapine. Educational material, such as leaflets or videos, could be developed and distributed to achieve this goal. The information provided in this article may be useful to improve disease burden and support healthcare professionals, patients, and caregivers navigating the complex pathways to TRS management.

Once-daily versus divided dosing regimens of clozapine: A cross-sectional study in Singapore

INTRODUCTION

Clozapine is recognized as the gold standard medication for treatment-resistant schizophrenia. Despite the general recommendation of administering in a divided dosing regimen, clozapine is often prescribed once daily at night in clinical practice. This study aims to compare patient characteristics, psychiatric symptoms, side effects, and plasma concentration of clozapine between once-daily dosing and divided dosing regimens.

METHODS

This cross-sectional study included 159 participants with treatment-resistant schizophrenia or schizoaffective disorder. Participant's demographic information, anthropometric data, and medical history were collected. Their psychiatric symptoms, cognition, functioning, and side effects were evaluated.

RESULTS

Once-daily dosing regimen was associated with younger age and competitive employment. Lower clinical symptom severity, better functioning and cognitive performance were observed in the once-daily dosing group. Lower daily dose of clozapine, trough plasma concentrations of clozapine and norclozapine were also significantly associated with once-daily dosing regimen.

CONCLUSION

The study results support once-daily dosing of clozapine as a viable option to selected patients in clinical practice, as no association of severe symptoms or side effects were associated with once-daily dosing regimen. More studies are needed to examine the relationship between clinical outcomes and clozapine dosing regimen.

The impact of adjunctive aripiprazole on QT interval: A 12-week open label study in patients on olanzapine, clozapine or risperidone

OBJECTIVE

To evaluate the effect of adjunct aripiprazole on QT of patients clinically stabilized on atypical antipsychotics.

METHODS

The dataset was from an open-label 12-week prospective trial that evaluated adjunctive use of 5 mg/day of aripiprazole on metabolic profile in patients with schizophrenia, or schizoaffective disorder stabilized on olanzapine, clozapine, or risperidone. Bazett-corrected QT (QTc) was manually calculated from ECGs measured at baseline (before aripiprazole) and week 12, by two doctors blind to the diagnosis and atypical antipsychotic. The change in QTc (∆QTc: baseline QTc-week 12 QTc) and the number of participants in normal, borderline, prolonged, and pathological groups after 12 weeks were analyzed.

RESULTS

Fifty-five participants, mean age of 39.3 (SD 8.2) years, were analyzed. The ∆QTc after 12 weeks was 5.9 ms (p = 0.143) for the whole sample; 16.4 ms (p = 0.762), 3.7 ms (p = 0.480) and 0.5 ms (p = 0.449), for the clozapine, risperidone and olanzapine group, respectively. There was no significant statistical difference comparing the change in QTc overall, and between atypical antipsychotic groups, when evaluating from baseline to endpoint. However, stratifying the sample based on sex-dependent QTc cut-offs showed a 45% decrease in abnormal QTc readings (p = 0.049) after aripiprazole initiation; 20 subjects had abnormal QTc at baseline, while only 11 subjects had abnormal QTc at 12 weeks. 25.5% of participants showed a reduction in at least one QTc severity group, while 65.5% had no change and 9.0% worsened in QTc group, after 12 weeks of adjunct aripiprazole.

CONCLUSION

Low-dose adjunctive aripiprazole did not prolong QTc in patients stabilized on either olanzapine, risperidone, or clozapine. More controlled studies evaluating the QTc effect of adjunctive aripiprazole should be done to confirm and support these findings.

Clozapine Once-Daily Versus Divided Dosing Regimen: A Cross-sectional Study in Japan

OBJECTIVE

Clozapine is generally recommended to be prescribed in a divided dosing regimen based on its relatively short plasma half-life. However, there has been little evidence to support the superiority of divided dosing of clozapine over once-daily dosing. To our knowledge, there have been no studies examining differences in actual plasma concentrations or adverse effects between the 2 dosing strategies of clozapine. We aimed to compare actual plasma concentrations of clozapine between once-daily and divided dosing regimens, and to examine the relationships of these regimens with psychiatric symptoms and adverse effects of clozapine.

METHODS

We analyzed data from 108 participants of a previous study conducted in 2 hospitals in Japan. A population pharmacokinetic model was used to estimate the peak and trough plasma concentrations of clozapine based on actual plasma concentrations. We evaluated psychiatric symptoms with the Brief Evaluation of Psychosis Symptom Domains and adverse effects of clozapine with the Glasgow Antipsychotic Side-effects Scale for Clozapine.

RESULTS

The estimated peak and trough plasma concentrations of clozapine did not differ significantly between once-daily and divided dosing regimens. There were no significant differences in psychiatric symptoms except for depression/anxiety or subjective adverse effects of clozapine between the 2 dosing strategies.

CONCLUSIONS

Our findings tentatively support the feasibility and clinical utility of once-daily dosing of clozapine in clinical practice. Further studies are needed to replicate these findings and determine causality between dosing strategies and clinical outcomes.

Risk factors for clozapine-induced central nervous system abnormalities in Japanese patients with treatment-resistant schizophrenia

The purpose of this study was to assess the risk factors for clozapine-induced central nervous system (CNS) abnormalities (i.e., electroencephalogram [EEG] abnormalities, myoclonus, and seizures). We retrospectively analyzed data from 106 patients with schizophrenia who received clozapine treatment through our hospital. A review of the EEG recordings showed that 71 of these patients (67.0 %) developed CNS abnormalities after initiating clozapine treatment. EEG abnormalities, myoclonus, and seizures occurred in 53.8 %, 38.7 %, and 8.5 % of the patients, respectively. Multivariate logistic regression analysis showed that the risk factors for clozapine-induced CNS abnormalities were concomitant lithium usage (odds ratio, 4.560; 95 % confidence interval, 1.750-11.900) and shorter illness durations before clozapine initiation (odds ratio, 0.796; 95 % confidence interval, 0.649-0.976). However, plasma clozapine levels and the usage of antiepileptics did not exhibit associations with the risks of CNS abnormalities. Clinicians should monitor their patients for incident CNS abnormalities when administering lithium in combination with clozapine regardless of plasma clozapine levels or the usage of antiepileptics. This is especially true for patients with short illness durations.

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.

Mental Health Nurses' Knowledge of Clozapine

Clozapine, sold under the brand name Clozaril, is an antipsychotic medication prescribed since the 1970s as an effective treatment for individuals with treatment resistive schizophrenia. Medical experts have produced extensive literature on the need for close monitoring as this medication can cause life threatening adverse effects. Mental health nurses play a vital role in the management of clozapine, however to date just one study specifically examines psychiatric/mental health nurse's knowledge of this medication. Nurses need to be aware of the adverse effects and be able to provide psychoeducation to help support and inform clients prescribed this medication. This study used a survey questionnaire. A clozapine knowledge questionnaire with 18 questions was developed by De Hert et al. to explore psychiatric/mental health nurse's knowledge on the adverse effects of clozapine. We distributed a shortened version of this knowledge questionnaire (12-multi-choice questions) to 209 mental health nurses working within one Irish Mental Health Service. One hundred and twenty-nine (n = 129) nurses completed the questionnaire with a response rate of 62%. Our results indicated that over 40% of mental nurses had not received sufficient education on clozapine medication during their formal education. We found that just 50% of participants scored over six correct questions out of 12 questions on various areas of knowledge related to clozapine medication. We identified gaps in knowledge on clozapine medication in relation to on myocarditis, epilepsy and metabolic syndrome. We highlighted gaps in mental health nurses' knowledge of clozapine medication that need to be improved in order to help clients. We advocate additional education on clozapine medication at undergraduate education and through educational packages at the service level.

Clozapine associated cardiotoxicity: Issues, challenges and way forward

OBJECTIVE

To review the published literature on clozapine associated cardiotoxicity (CACT), summarize diagnostic features, and evaluate monitoring procedures for safe clozapine re-challenge.

RESULTS

Clozapine-associated Myocarditis (CAM) - Incidence of early myocarditis (≤2 months) is infrequent but serious. Clinical diagnosis is confounded by variability in presentation and non-specificity of symptoms. Re-challenge considerations include clozapine impact on symptomatic severity and associated disability and risk of suicidality. Re-challenging is recommended only after full clinical resolution of myocarditis and cardiac function impairment, under closely controlled conditions, starting at very low dosage, extremely slow titration and frequent assays of lab and cardio biomarkers. Clozapine associated cardiomyopathy (CAC) -develops later but mortality has been reported at 12.5-24.0%. Re-challenge is generally not recommended due to paucity of outcome data. Monitoring Cardiac Toxicity: Plausible steps include closer clinical monitoring, repeated assays of biomarkers, and echocardiographic studies, and cardiac MRI changes with unremarkable findings of cardiac dysfunction with echocardiography. Subclinical clozapine associated cardiotoxicity is more prevalent than CAM and CAC. Diagnosis is often challenging due to non specific presentation. Active monitoring is recommended. Rechallenging is feasible but should be done under close monitoring conditions. A protocol is proposed based on literature review and clinical experience in order to reduce the risk of CACT.

CONCLUSION

Clozapine-associated myocarditis and cardiomyopathy may have been underreported worldwide. Identification of subclinical cardiotoxic effects can improve outcomes by earlier recognition before clinical manifestations of cardiac impairments. A pragmatic close clinical monitoring protocol including cardiac biomarkers aimed at timely detection of cardiac toxicity, in the initial phase of treatment is proposed.

Cellular Uptake of the Atypical Antipsychotic Clozapine Is a Carrier-Mediated Process

The weak base antipsychotic clozapine is the most effective medication for treating refractory schizophrenia. The brain-to-plasma concentration of unbound clozapine is greater than unity, indicating transporter-mediated uptake, which has been insufficiently studied. This is important, because it could have a significant impact on clozapine's efficacy, drug-drug interaction, and safety profile. A major limitation of clozapine's use is the risk of clozapine-induced agranulocytosis/granulocytopenia (CIAG), which is a rare but severe hematological adverse drug reaction. We first studied the uptake of clozapine into human brain endothelial cells (hCMEC/D3). Clozapine uptake into cells was consistent with a carrier-mediated process, which was time-dependent and saturable ( V_max = 3299 pmol/million cells/min, K_m = 35.9 μM). The chemical inhibitors lamotrigine, quetiapine, olanzapine, prazosin, verapamil, indatraline, and chlorpromazine reduced the uptake of clozapine by up to 95%. This could in part explain the in vivo interactions observed in rodents or humans for these compounds. An extensive set of studies utilizing transporter-overexpressing cell lines and siRNA-mediated transporter knockdown in hCMEC/D3 cells showed that clozapine was not a substrate of OCT1 (SLC22A1), OCT3 (SLC22A3), OCTN1 (SLC22A4), OCTN2 (SLC22A5), ENT1 (SLC29A1), ENT2 (SLC29A2), and ENT4/PMAT (SLC29A4). In a recent genome-wide analysis, the hepatic uptake transporters SLCO1B1 (OATP1B1) and SLCO1B3 (OATP1B3) were identified as additional candidate transporters. We therefore also investigated clozapine transport into OATP1B-transfected cells and found that clozapine was neither a substrate nor an inhibitor of OATP1B1 and OATP1B3. In summary, we have identified a carrier-mediated process for clozapine uptake into brain, which may be partly responsible for clozapine's high unbound accumulation in the brain and its drug-drug interaction profile. Cellular clozapine uptake is independent from currently known drug transporters, and thus, molecular identification of the clozapine transporter will help to understand clozapine's efficacy and safety profile.