Changes in Plasma Clozapine Levels after Smoking Cessation in Japanese Inpatients with Schizophrenia: A Retrospective Cohort Study

Masaru Tsukahara, Ryuhei So, Yuji Yada, Masafumi Kodama, Yoshiki Kishi, Norihito Yamada

Research output: Contribution to journalArticlepeer-review

Abstract

Although reported for Caucasians, changes in plasma clozapine levels after smoking cessation in East Asians remain unclear. We here investigated plasma clozapine levels before and after smoking cessation in Japanese inpatients with schizophrenia. We conducted a retrospective chart review of 14 inpatients with schizophrenia who were being treated with clozapine between June 1, 2019, and July 31, 2019 and who were smokers as of July 1, 2019, the day on which a smoking ban was instituted in the tertiary public psychiatric hospital. The primary outcome was individual differences in plasma clozapine levels between before and after the smoking ban, which were compared using paired t-tests. The mean plasma clozapine level was significantly increased, by 213.4 ng/mL (95% CI 119.9-306.8; p<0.01) or 53.2%. Four of the 14 inpatients experienced clinically significant side effects, such as myoclonus, drooling, and amnesia, due to the development of high plasma clozapine levels. Our findings indicated that close monitoring of plasma clozapine levels before and after smoking cessation and prior dose adjustment of clozapine may be necessary, to prevent a significant risk of developing high plasma clozapine levels, even in Japanese patients.

Original languageEnglish
Pages (from-to)137-143
Number of pages7
JournalActa medica Okayama
Volume76
Issue number2
DOIs
Publication statusPublished - 2022

Keywords

  • Asian
  • Clozapine
  • Schizophrenia
  • Smoking

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

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