Plasma concentrations of quetiapine, n-desalkyquetiapine, o-desalkylquetiapine, 7-hydroxyquetiapine and quetiapine sulfoxide in relation to quetiapine dose, formulation and other factors

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Abstract

Background: N-Desalkylquetiapine may be a pharmacologically active quetiapine metabolite. However, information on plasma concentrations of N-desalkylquetiapine and other quetiapine metabolites attained during quetiapine therapy is scant. The aim of this study was to investigate plasma concentrations of quetiapine, N-desalkylquetiapine, O-desalkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide attained during therapy and analyze the data with respect to prescribed dose and other variables.

Method: Quetiapine and its metabolites were measured in plasma samples submitted for quetiapine therapeutic drug monitoring (2009–2011). Concentration, metabolic ratio, and concentration corrected for dose (C/D) were investigated against quetiapine dose, age, sex, and formulation. Sample results were excluded if nonadherence with therapy was queried.

Results: There were 99 samples from 59 patients. N-Desalkylquetiapine plasma concentrations showed the strongest correlation with dose of all analytes, but O-desalkylquetiapine and quetiapine sulfoxide were strongly correlated to plasma quetiapine concentrations. There was no significant difference in C/D for any analyte between males and females and no correlation to age. Quetiapine and quetiapine sulfoxide C/D were significantly different (P < 0.01) between patients prescribed immediate- and extended-release formulations. Quetiapine, 7-hydroxyquetiapine and quetiapine sulfoxide C/D showed significant variation (P < 0.02) between those samples taken 10–14 hours postdose as compared with that of 16–24 hours postdose, but there was no significant effect as regards N-desalkylquetiapine.

Conclusions: Plasma quetiapine, O-desalkylquetiapine, 7-hydroxyquetiapine, and quetiapine sulfoxide concentrations were significantly affected by formulation and/or time since last dose. Plasma N-desalkylquetiapine concentrations were not affected by either factor therefore may be a better marker for quetiapine exposure than plasma quetiapine concentrations.
Original languageEnglish
Pages (from-to)415-421
Number of pages7
JournalTherapeutic Drug Monitoring
Volume34
Issue number4
DOIs
Publication statusPublished - Aug 2012

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