Clozapine-induced gastrointestinal hypomotility: presenting features and outcomes, UK pharmacovigilance reports, 1992-2017

Revealing the reporting disparity: VigiBase highlights underreporting of clozapine in other Western European countries compared to the UK

BACKGROUND

Pharmacovigilance studies indicate clozapine history is marked by adverse drug reactions (ADRs).

OBJECTIVE

In a 2021 article, the United Kingdom (UK) had >90 % of European clozapine-related fatal outcomes in VigiBase, the World Health Organization's pharmacovigilance database. Two possibly opposing hypotheses could explain this disparity: 1) fewer reported fatal outcomes in other Western European countries mainly reflect underreporting to VigiBase, and 2) the higher number of UK reports reflects higher real relative mortality.

METHODS

VigiBase reports from clozapine's introduction to December 31, 2022, were studied for ADRs and the top 10 causes of fatal outcomes. The UK was compared with 11 other top reporting Western countries (Germany, Denmark, France, Finland, Ireland, Italy, Netherlands, Norway, Spain, Sweden and Switzerland). Nine countries (except Ireland and Switzerland) were compared after controlling for population and clozapine prescriptions.

RESULTS

The UK accounted for 29 % of worldwide clozapine-related fatal outcomes, Germany 2 % and <1 % in each of the other countries. The nonspecific label "death" was the top cause in the world (46 %) and in the UK (33 %). "Pneumonia" was second in the world (8 %), the UK (12 %), Ireland (8 %) and Finland (14 %). Assuming that our corrections for population and clozapine use are correct, other countries underreported only 1-10 % of the UK clozapine fatal outcome number.

CONCLUSIONS

Different Western European countries consistently underreport to VigiBase compared to the UK, but have different reporting/publishing styles for clozapine-related ADRs/fatal outcomes. Three Scandinavian registries suggest lives are saved as clozapine use increases, but this cannot be studied in pharmacovigilance databases.

Clozapine-Induced Refractory Colonic Pseudo-Obstruction

The management of treatment-resistant schizophrenia (TRS) is challenging as the medications involved, often atypical antipsychotics, have a host of associated adverse effects. While complications such as agranulocytosis are well established and necessitate close hematological monitoring, the gastrointestinal effects of particular atypical antipsychotics, such as clozapine, are recognized to a lesser extent. The following case of TRS leading to chronic treatment-resistant pseudo-obstruction, eventually requiring total colectomy, highlights the considerable sequelae of clozapine on the gastrointestinal tract. Beyond the effects of severe constipation, the possible implications of ischemic colitis, stercoral perforation, and intraabdominal sepsis warrant a degree of caution when prescribing such medication. This study sheds light on the importance of monitoring bowel motility when administering antipsychotics, particularly clozapine, to avoid these deleterious consequences.

A population pharmacokinetic model to guide clozapine dose selection, based on age, sex, ethnicity, body weight and smoking status

AIMS

Guidance on clozapine dosing in treatment-resistant schizophrenia is based largely on data from White young adult males. This study aimed to investigate the pharmacokinetic profiles of clozapine and N-desmethylclozapine (norclozapine) across the age range, accounting for sex, ethnicity, smoking status and body weight.

METHODS

A population pharmacokinetic model, implemented in Monolix, that linked plasma clozapine and norclozapine via a metabolic rate constant, was used to analyse data from a clozapine therapeutic drug monitoring service, 1993-2017.

RESULTS

There were 17 787 measurements from 5960 patients (4315 male) aged 18-86 years. The estimated clozapine plasma clearance was reduced from 20.2 to 12.0 L h-1 between 20 and 80 years. Model-based dose predictions to attain a predose plasma clozapine concentration of 0.35 mg L-1 was 275 (90% prediction interval 125, 625) mg day-1 in nonsmoking, White males weighing 70 kg and aged 40 years. The corresponding predicted dose was increased by 30% in smokers, decreased by 18% in females, and was 10% higher and 14% lower in otherwise analogous Afro-Caribbean and Asian patients, respectively. Overall, the predicted dose decreased by 56% between 20 and 80 years.

CONCLUSION

The large sample size and wide age range of the patients studied allowed precise estimation of dose requirements to attain predose clozapine concentration of 0.35 mg L-1 . The analysis was, however, limited by the absence of data on clinical outcome and future studies are required to determine optimal predose concentrations specifically in those aged over 65 years.

Clozapine Optimization: A Delphi Consensus Guideline From the Treatment Response and Resistance in Psychosis Working Group

BACKGROUND AND HYPOTHESIS

There is limited evidence to guide the approaches to clozapine treatment. Accordingly, an international initiative was undertaken with the aim of developing consensus recommendations for the optimization of clozapine monotherapy.

STUDY DESIGN

We conducted an online Delphi survey among members of the Treatment Response and Resistance in Psychosis (TRRIP) working group comprising experts from twenty-nine countries. The threshold criterion for a consensus recommendation was ≥ 75% agreement ("agree" and "strongly agree" responses) on a question. Agreement of ≥ 50% but < 75% in a second or third Delphi round was deemed to provide guidance.

STUDY RESULTS

Forty-nine (first round), 32 (second round), and 48 (third round) of the 91 current TRRIP members participated. Expert recommendations at ≥ 75% comprised second-line treatment with clozapine in cases of persistent positive symptoms with co-occurring extrapyramidal symptoms, tardive dyskinesia, or suicidality/aggression. There was considerable disagreement on myocarditis screening parameters. The management of somatic and neuropsychiatric adverse drug reactions warrants further research for more evidence-based recommendations. Rechallenge with clozapine was recommended for eosinophilia, sinus tachycardia and fever and guidance (agreement ≥ 50%) was reached for pneumonia and thrombocytopenia.

CONCLUSIONS

Given the limited evidence available, this consensus-based series of recommendations and guidance statements supports clinical decision-making to optimize clozapine monotherapy and provides guidance for future research in treatment-resistant schizophrenia.

Second to none: rationale, timing, and clinical management of clozapine use in schizophrenia

Despite its enduring relevance as the single most effective and important evidence-based treatment for schizophrenia, underutilization of clozapine remains considerable. To a substantial degree, this is attributable to a reluctance of psychiatrists to offer clozapine due to its relatively large side-effect burden and the complexity of its use. This underscores the necessity for continued education regarding both the vital nature and the intricacies of clozapine treatment. This narrative review summarizes all clinically relevant areas of evidence, which support clozapine's wide-ranging superior efficacy - for treatment-resistant schizophrenia (TRS) and beyond - and make its safe use eminently feasible. Converging evidence indicates that TRS constitutes a distinct albeit heterogeneous subgroup of schizophrenias primarily responsive to clozapine. Most importantly, the predominantly early onset of treatment resistance and the considerable decline in response rates associated with its delayed initiation make clozapine an essential treatment option throughout the course of illness, beginning with the first psychotic episode. To maximize patients' benefits, systematic early recognition efforts based on stringent use of TRS criteria, a timely offer of clozapine, thorough side-effect screening and management as well as consistent use of therapeutic drug monitoring and established augmentation strategies for suboptimal responders are crucial. To minimize permanent all-cause discontinuation, re-challenges after neutropenia or myocarditis should be considered. Owing to clozapine's unique efficacy, comorbid conditions including substance use and most somatic disorders should not dissuade but rather encourage clinicians to consider clozapine. Moreover, treatment decisions need to be informed by the late onset of clozapine's full effects, which for reduced suicidality and mortality rates may not even be readily apparent. Overall, the singular extent of its efficacy combined with the high level of patient satisfaction continues to distinguish clozapine from all other available antipsychotics.

Reflections on the Lack of Consideration of Ethnic Ancestry to Stratify Clozapine Dosing

This review article argues against trusting standard clozapine references, including the US package insert, because they do not include advances in the sciences of pharmacokinetics and pharmacovigilance and ignore the effects of ethnic ancestry on therapeutic dosing. The minimum therapeutic dose leading to the minimum therapeutic concentration of 350 ng/mL in serum/plasma can be used to compare individuals/groups with treatment-resistant schizophrenia. The US clozapine package insert recommends targeting doses of 300-450 mg/day and, subsequently, increments of up to 100 mg with a maximum dose of 900 mg/day. Ethnic ancestry is defined by DNA ancestry group. Asians (people with ancestry ranging from Pakistan to Japan) and Indigenous Americans are similar in clozapine dosing; their average clozapine minimum therapeutic dose ranged from 166 mg/day (female non-smokers) to 270 mg/day (male smokers). For those with European ancestry, average clozapine minimum therapeutic doses ranged from 236 mg/day (female non-smokers) to 368 mg/day (male smokers). Based on limited studies, Black (African sub-Saharan ancestry) patients may be treated with typical US doses (300-600 mg/day), assuming no poor metabolism (PM) status. Ancestry's impact on clozapine lethality in four countries is discussed (two countries with highly homogenous populations, Denmark and Japan, and two countries with increasingly heterogenous populations due to immigration, Australia and the UK). An international guideline with 104 authors from 50 countries/regions was recently published, providing 6 personalized clozapine titration schedules for adult inpatients (3 ancestry groups and PM/non-PM schedules) and recommending c-reactive protein monitoring at baseline and weekly for 4 weeks.

Lubiprostone for the Treatment of Clozapine-Induced Constipation: A Case Series

Clozapine-induced constipation is an increasingly recognized adverse reaction that frequently impairs optimal management of treatment-resistant schizophrenia. The Food and Drug Administration recently strengthened an existing warning for clozapine, citing constipation as an adverse effect that can progress to serious bowel complications. Evidence-based guidelines for laxatives in the management of clozapine-induced constipation remain scarce, and there is a general need for improved algorithms in the management of this common condition. Lubiprostone is a relatively new laxative that has labeled indications for opioid-induced constipation, irritable bowel syndrome with constipation, and chronic idiopathic constipation. This case series describes clinical pearls associated with four cases of treatment-resistant schizophrenia who underwent treatment of clozapine-induced constipation with lubiprostone. The findings of this case series suggest that there may be significant therapeutic potential in the utilization of lubiprostone for the management of clozapine-induced constipation with a low risk of adverse reactions. The study of lubiprostone benefit (i.e., without coadministration of other laxatives) continues to be of prominent interest in understanding its ability to manage clozapine-induced constipation.