Clozapine ultrarapid metabolism during weak induction probably exists but requires careful diagnosis. A literature review, five new cases and a proposed definition

Pharmacovigilance in Action: Utilizing VigiBase Data to Improve Clozapine Safety

Purpose

Clozapine is an antipsychotic which was approved in 1989 for treatment-resistant schizophrenia in the United States (US). There were few randomized trials before its approval and potentially lethal clozapine adverse drug reactions (ADRs), such as agranulocytosis and myocarditis were identified by pharmacovigilance. VigiBase, the WHO global database, is a cornerstone of international pharmacovigilance efforts for ADR identification during post-marketing surveillance. This systematic review of the literature explores additional contributions to the knowledge of clozapine ADRs from recent VigiBase studies.

Methods

Using the terms "clozapine AND VigiBase" we conducted an article search in PubMed on September 5, 2024. Of the 29 articles, 11 were excluded and 18 described in the Results section.

Results

All clozapine ADRs were described in two VigiBase studies. One on pregnancy indicated no increased risk with clozapine compared with other antipsychotics; the other reported 191,557 clozapine ADRs, including 22,956 fatal outcomes through January 15, 2023, and paid attention to the reporting style of the top 4 reporting countries (the US, the United Kingdom, Canada and Australia). Infections were described in three VigiBase studies where clozapine treatment was associated with infections, respiratory aspiration, and pneumonia. Rapid titration can lead to localized clozapine-induced inflammations including myocarditis, pericarditis or pancreatitis, or generalized inflammations such as drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome. Clozapine-induced inflammation was described in four VigiBase studies, two focused on all ages (myocarditis and DRESS) and two on youth (myocarditis and another on pericarditis and pancreatitis). Other specific ADRs were described in nine VigiBase studies (hematological malignancies, rhabdomyolysis, sialorrhea, seizures, diabetes mellitus, drug-induced parkinsonism, withdrawal symptoms, and suicidal behaviors).

Conclusion

The spectrum of respiratory aspiration - aspiration pneumonia - pneumonia and other infections are significant causes of fatal outcomes in clozapine-treated patients. Clozapine had anti-suicidal effects versus other antipsychotics across all VigiBase labels of suicidal behavior.

Status of the implementation of pharmacogenetics in clinical practice in Spain: from regional to national initiatives

INTRODUCTION

Pharmacogenetics (PGx) has the potential to improve patient care, allowing to transform medical interventions by providing personalized therapeutic strategies. Scientific evidence supports the use of PGx in clinical practice and international organizations are developing clinical guidelines to facilitate the utilization of PGx testing. However, clinical implementation of PGx is limited and unequal worldwide.

CONTENT

This review summarizes regional and national Spanish initiatives to implement PGx in the clinical practice.

SUMMARY AND OUTLOOK

Diverse strategies to implement PGx in healthcare are applied across countries or even in the different regions of a specific country. Such was the case of Spain, a European country with 17 Autonomous Regions and two Autonomous Cities, each one with capacity to manage their own healthcare systems. Nevertheless, during the past years, many initiatives and strategies have been launched in Spain to develop different aspects of PGx. Importantly, the National Healthcare System has approved a PGx testing catalogue. This review highlights the crucial work and efforts of scientific societies (like the Spanish Society of Pharmacogenetics and Pharmacogenomics), of experts in PGx, of healthcare providers and of governmental parties in the implementation of PGx to personalize patient therapy, focused in Spain.

When, Why and How to Re-challenge Clozapine in Schizophrenia Following Myocarditis

Clozapine-induced myocarditis (CIM) is among the most important adverse events limiting the use of clozapine as the most effective treatment for schizophrenia. CIM necessitates the immediate termination of clozapine, often resulting in its permanent discontinuation with considerable detrimental effects on patients' psychopathology and long-term outcome. Consequently, a clozapine re-challenge after CIM is increasingly regarded as a viable alternative, with published reports indicating a success rate of approximately 60%. However, published cases of re-challenges after CIM remain limited. Here, we provide a narrative review of the current state of research regarding the epidemiology, pathophysiology, risk factors, diagnosis and clinical management of CIM as well as a synthesis of current recommendations for re-challenging patients after CIM. This includes a step-by-step guide for this crucial procedure based on the current evidence regarding the pathophysiology and risk factors for CIM. Slow dose titration regimes and addressing risk factors including concomitant valproate and olanzapine are crucial both to prevent CIM and to ensure a safe and successful re-challenge. Furthermore, we discuss the utility of C-reactive protein, troponin, N-terminal-pro hormone and brain natriuretic peptide, therapeutic drug-monitoring and cardiac magnetic resonance imaging for CIM screening and diagnosis as well as for post-CIM re-challenges.

How can we better address the pharmacokinetics of antipsychotics in children and adolescents?

INTRODUCTION

Despite a steady increase of antipsychotic prescriptions in children and adolescents, knowledge about pharmacokinetics and dosing of antipsychotics in children and adolescents remains limited.

AREAS COVERED

We discuss seven issues with major impact on the pharmacokinetics of antipsychotics in youth: estrogens, ii) obesity, iii) ethnicity, iv) smoking, v) inflammation, vi) drug-drug interactions (DDIs), and vii) pharmacogenetics. Despite their major impact, these issues have not been adequately considered in the context of dosing algorithms for antipsychotics in youth. A simple tool to quantify the impact of these pharmacokinetics issues on antipsychotics is therapeutic drug monitoring (TDM), which refers to the quantification of the prescribed medication in the blood of the patients, as a surrogate for the peripheral antipsychotic exposure. We also provide summary tables extrapolated from the adult literature on metabolism, therapeutic reference ranges (TRRs) and DDIs.

EXPERT OPINION

Despite considerable experience with TDM for antipsychotics in the management of other patient subgroups, TDM use for antipsychotics in children and adolescents may be limited with TRRs invariably being extrapolated from adult patients. Advancing TDM knowledge is expected to help clinicians address the special properties of pharmacokinetics of antipsychotics and ultimately enable antipsychotic dose individualization in youth.

Promoting safer and wider worldwide use of clozapine

This issue focuses on the past, the present and the future of clozapine. Of the 43 clozapine articles, nine are historical articles dealing with the past, 29 deal with the present and five with laboratory assays which may influence its future use. These 43 articles include 219 different authors from 56 countries/regions and five continents.

Developments in pharmacogenetics, pharmacogenomics, and personalized medicine

The development of Pharmacogenetics and Pharmacogenomics in Western Europe is highly relevant in the worldwide scenario. Despite the usually low institutional support, many research groups, composed of basic and clinical researchers, have been actively working for decades in this field. Their contributions made an international impact and paved the way for further studies and pharmacogenomics implementation in clinical practice. In this manuscript, that makes part of the Special Issue entitled Spanish Pharmacology, we present an analysis of the state of the art of Pharmacogenetics and Pharmacogenomics research in Europe, we compare it with the developments in Spain, and we summarize the most salient contributions since 1988 to the present, as well as recent developments in the clinical application of pharmacogenomics knowledge. Finally, we present some considerations on how we could improve translation to clinical practice in this specific scenario.

Evidence for Therapeutic Drug Monitoring of Atypical Antipsychotics

Second-generation antipsychotics (SGAs), also known as atypical antipsychotics, are a newer class of antipsychotic drugs used to treat schizophrenia, bipolar disorder, and related psychiatric conditions. The plasma concentration of antipsychotic drugs is a valid measure of the drug at its primary target structure in the brain, and therefore determines the efficacy and safety of these drugs. However, despite the well-known high variability in pharmacokinetics of these substances, psychiatric medication is usually administered in uniform dosage schedules. Therapeutic drug monitoring (TDM), as the specific method that can help personalised medicine in dose adjustment according to the characteristics of the individual patient, minimizing the risk of toxicity, monitoring adherence, and increasing cost-effectiveness in the treatment, thus seems to be an elegant tool to solve this problem. Non-response to therapeutic doses, uncertain adherence to medication, suboptimal tolerability, or pharmacokinetic drug-drug interactions are typical indications for TDM of SGAs. This review aims to summarize an overview of the current knowledge and evidence of the possibilities to tailor the dosage of selected SGAs using TDM, including the necessary pharmacokinetic parameters for personalised pharmacotherapy.