Plasma Clozapine and Norclozapine in Patients Prescribed Different Brands of Clozapine (Clozaril, Denzapine, and Zaponex)

Lewis Couchman*, Phillip Edgar Morgan, Edgar Pathrose Spencer, Atholl Johnston, Bob Flanagan

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    16 Citations (Scopus)


    To investigate the bioequivalence of the three clozapine brands licensed in the United Kingdom, we compared plasma clozapine and norclozapine in therapeutic drug monitoring samples from patients switched from Clozaril to either Denzapine or Zaponex tablets. For Clozaril/Denzapine, the median prescribed clozapine dose was 450 mg/day (range, 125-850 mg/day) (n = 66) and the median time between samples was 16 weeks. The Clozaril/Zaponex comparison (n = 57) was not dose-controlled; the median Clozaril dose was 450 mg/day (range, 150-900 mg/day) and the median Zaponex dose 400 mg/day (range, 100-850 mg/day). The median time between samples was 19 weeks. There was no significant difference in mean plasma clozapine and norclozapine concentration before and after switching in either case, although some individual results showed clinically relevant concentration differences. Plasma norclozapine showed greater reproducibility between samples than clozapine. The different brands of clozapine available in the United Kingdom show bioequivalence. Nevertheless, careful monitoring of mental state, smoking habit, adherence, and of possible life-threatening adverse effects is mandatory if the drug is to be used safely.

    Original languageEnglish
    Pages (from-to)624-627
    Number of pages4
    JournalTherapeutic Drug Monitoring
    Issue number5
    Publication statusPublished - Oct 2010


    • clozapine brands
    • bioequivalence
    • clozapine TDM
    • switching brands


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