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Olanzapine disposition in humans is unrelated to CYP1A2 and CYP2D6 phenotypes
1Division of Clinical Pharmacology, Norrland University Hospital, Umeå, Sweden. staffan.hagg@pharm.umu.se
Objective:
Limited data suggest that CYP1A2 and CYP2D6 are involved in the metabolism of olanzapine. The purpose of this study was to further elucidate the role of these enzymes in the disposition of olanzapine in vivo.
Methods:
Seventeen healthy non-smoking male volunteers were included in the study. Five subjects were CYP2D6 poor metabolisers (PMs), and 12 were CYP2D6 extensive metabolisers (EMs). All subjects received a single oral dose of 7.5 mg olanzapine, and serum concentrations were measured for 96 h using gas chromatography. A cross-over study was undertaken in the 12 CYP2D6 EMs who at least 2 weeks before or after the olanzapine dose received a single oral dose of 200 mg caffeine. The concentrations of caffeine and paraxanthine were measured in saliva 10 h after caffeine intake, and the paraxanthine/caffeine ratio was calculated as a measure of CYPIA2 activity.
Results:
A threefold inter-individual variability in oral clearance (CLoral) and maximum serum concentration (Cmax) of olanzapine was observed and a 2.3-fold inter-individual variability in CYPIA2 activity. There was no significant correlation between CYP1A2 activity and oral clearance of olanzapine (r=-0.19, P=0.56). Moreover, there were no significant differences in any of the olanzapine pharmacokinetic parameters between the CYP2D6 PMs and EMs (CLoral=0.246 l h(-1) kg(-1) and 0.203 l h(-1) kg(-1), respectively, P=0.30).
Conclusion:
Neither CYP1A2 nor CYP2D6 seem to have a dominating role in olanzapine biotransformation after intake of a single dose.
Insights
This study found that neither CYP1A2 nor CYP2D6 significantly impacts olanzapine metabolism. Olanzapine
Area of Science:
- Pharmacology
- Drug Metabolism
- Enzyme Kinetics
Background:
- Limited data suggest CYP1A2 and CYP2D6 involvement in olanzapine metabolism.
- Understanding these enzyme roles is crucial for predicting drug disposition.
Purpose of the Study:
- To investigate the in vivo role of CYP1A2 and CYP2D6 in olanzapine metabolism.
- To determine if genetic variations in these enzymes affect olanzapine pharmacokinetics.
Main Methods:
- Seventeen healthy male volunteers (5 CYP2D6 poor metabolizers, 12 extensive metabolizers) received a single 7.5 mg oral dose of olanzapine.
- CYP1A2 activity was assessed using caffeine and paraxanthine ratios.
- Olanzapine serum concentrations were measured over 96 hours via gas chromatography.
Main Results:
- Significant inter-individual variability in olanzapine oral clearance and Cmax was observed.
- No significant correlation was found between CYP1A2 activity and olanzapine oral clearance.
- No significant differences in olanzapine pharmacokinetic parameters were detected between CYP2D6 poor and extensive metabolizers.
Conclusions:
- CYP1A2 does not appear to play a dominant role in the biotransformation of a single dose of olanzapine.
- CYP2D6 genetic polymorphism does not significantly influence the pharmacokinetics of olanzapine after a single oral dose.
- Neither enzyme is a major determinant of olanzapine disposition in vivo.