ArticleNPJ schizophrenia2020
Undetectable or subtherapeutic serum levels of antipsychotic drugs preceding switch to clozapine.
Article in NPJ schizophrenia, 2020. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 5 papers.
What it found
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Who cites it
5 citing papers in PubMed.
- Genetic overlap between treatment-resistant schizophrenia and smoking initiation.The international journal of neuropsychopharmacology · 2026Article
- Article
- Current Status of Therapeutic Drug Monitoring in Mental Health Treatment: A Review.Pharmaceutics · 2022Review
- Self-Report for Measuring and Predicting Medication Adherence: Experts' Experience in Predicting Adherence in Stable Psychiatric Outpatients and in Pharmacokinetics.Patient preference and adherence · 2020Article
- Letter to the FDA Proposing Major Changes in the US Clozapine Package Insert Supported by Clozapine Experts Worldwide. Part I: A Review of the Pharmacokinetic Literature and Proposed Changes.Journal of clinical psychopharmacologyReview
Corrections and comments
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Authors and funding
5 authors.
Funding
No grant is acknowledged in the PubMed record.
Abstract
Adequate antipsychotic treatment intensity is required for defining treatment-resistant schizophrenia (TRS) and justifying clozapine treatment. We investigated the occurrence of undetectable or subtherapeutic serum levels of oral antipsychotics preceding switch to clozapine as an endpoint of TRS. For patients starting clozapine, 12-month retrospective reviews of antipsychotic serum concentration measurements were performed in a Norwegian therapeutic drug monitoring (TDM) database from 2005 to 2017. Undetectable levels in high-sensitive analytical assays defined 'no drug use', while levels <50% of the lower reference range defined 'subtherapeutic use'. Similar data were collected for patients switching to long-acting injectable (LAI) antipsychotics, as a reference of 'no or subtherapeutic drug use'. Nineteen of 353 patients initiating clozapine (5.4%) had a recent history of undetectable antipsychotic drug levels compared to 91 of 1048 (8.7%) initiating LAI. Another 19 patients starting clozapine (5.4%) had recent events of subtherapeutic levels. In conclusion, the present retrospective study may indicate that every 10th patient starting clozapine has a recent history of undetectable or subtherapeutic serum levels of oral antipsychotics. The clinical implications of the present study for the assessment of TRS should be investigated prospectively in further studies.
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