The relationship between plasma clozapine concentration and clinical outcome: a cross-sectional study

Yuji Yada, Kohei Kitagawa, Shinji Sakamoto, Atsushi Ozawa, Akihiro Nakada, Hiroko Kashiwagi, Yuko Okahisa, Soshi Takao, Manabu Takaki, Yoshiki Kishi, Norihito Yamada

Research output: Contribution to journalArticlepeer-review

24 Citations (Scopus)


Objective: There is no report that statistically evaluates the therapeutic reference (350–600 ng/ml) and adverse drug reaction (ADR) range (>1000 ng/ml) of clozapine (CLZ) recommended by the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) consensus guidelines in an isolated and large sampling study. Methods: We administered CLZ to 131 Japanese patients with treatment-resistant schizophrenia in a multicenter cross-sectional study. Plasma CLZ concentrations were assayed by high-performance liquid chromatography using trough sampling. The Brief Psychiatric Rating Scale (BPRS) and severe dose-dependent ADR (sedation, myoclonus, and seizures) were analyzed statistically after adjusting for possible confounders. Results: The daily CLZ dosage showed a moderately positive relationship with the plasma concentration (r = 0.49, p < 0.001). Every 100 ng/ml increase in plasma CLZ concentration improved the total BPRS score 1.95% (95% CI: 0.89–3.01, p < 0.001) and the odds ratio (OR) 1.38 (95% CI: 1.14–1.66, p = 0.001) for BPRS response. Compared with concentrations below 350 ng/ml CLZ, 350–600 ng/ml (11.12%; 95% CI: 2.52–19.72, p = 0.012) and 600–1000 ng/ml (11.05%; 95% CI: 2.40–19.71, p = 0.013) showed significant improvement in the total BPRS score. Dosages above 1000 ng/ml showed greater improvement (25.36%; 95% CI: 13.08–37.64, p < 0.001) of the total BPRS score but more severe ADRs than dosages below 1000 ng/ml (OR: 31.72; 95% CI: 1.04–968.81, p = 0.048). Conclusion: The AGNP therapeutic reference range (350–600 ng/ml) is useful, and a dose above 1000 ng/ml is potentially more effective but carries the risk of severe ADRs in the central nervous system.

Original languageEnglish
Pages (from-to)227-237
Number of pages11
JournalActa Psychiatrica Scandinavica
Issue number3
Publication statusPublished - Mar 2021


  • AGNP reference range
  • Schizophrenia
  • adverse drug reaction
  • plasma clozapine concentration
  • therapeutic drug monitoring

ASJC Scopus subject areas

  • Psychiatry and Mental health


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