Abstract
Background and objective: Conflicting therapeutic drug monitoring (TDM) results have been reported for risperidone and olanzapine. This study set out to examine the long-term pharmacokinetics of risperidone and olanzapine in a locked skilled nursing facility where medication administration was controlled by nursing staff.
Methods: TDM was performed in a long-term treatment protocol for risperidone and olanzapine in 67 refractory chronic schizophrenic patients in a locked, skilled nursing facility. TDM was performed 632 times in the risperidone group of 34 patients and 563 times in the olanzapine group of 33 patients. The logarithm of plasma concentrations were analysed through time by piecewise linear mixed model regressions adjusted for the logarithm of dose.
Results: We found risperidone plasma concentration/dose ratio (C/D) accumulation peaks of 49% at 2 months (from baseline concentration) and 9-hydroxy-risperidone and total moiety C/D accumulation peaks of 66% and 55% above the 2-month level at 6 months, which are somewhat similar to those found in our prior study that included a subset of data points analysed here. The risperidone conversion to 9-hydroxy-risperidone by cytochrome P450 (CYP) 2D6 suggests CYP2D6 inhibition or DNA down-regulation in the first 2 months. Olanzapine showed a C/D accumulation peak at 4 months of 31% above baseline, and a slower increase to 47% above baseline at 18 months with no clear plateau.
Conclusion: We identified five potential perturbations in the pharmacokinetics of risperidone and olanzapine that could potentially lead to adverse drug reactions. These long-term effects would not be captured by a standard 5-day pharmacokinetic TDM developmental testing model for antipsychotics, and a new model for characterizing variation in C/D by time course is therefore proposed. The time course of the accumulations identified suggests that both CYP inhibition and DNA regulatory mechanisms may be involved in the metabolism of these drugs. Long-term TDM can optimize treatment with risperidone and olanzapine and antipsychotics in general.
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Acknowledgements
This research was supported in part by grants from Specom Research, Fremont, CA, USA and Eli Lilly, Indianapolis, IN, USA. The authors thank Edward T. Morgan, PhD, Professor, Department of Pharmacology, Emory University School of Medicine, Rollins Research Center, Atlanta, Georgia for review and comments.
For additional review and comment the authors also thank Nancy Sambol, PhD, Thuy Vu, PhD and Julie Nelson, MBA from the Center for Drug Development Science at University of California, San Francisco, CA, USA (Carl Peck, Chairman), and Celia Moreno, MD (Medical Director), Joris Wiggers, MD (Psychiatry), and Barbara Liang, PhD (Pharmacology) from San Mateo County Mental Health, San Mateo, CA, USA, as well as Patrick Willems, MD, PhD, Tom Darling, PhD, Rocky Nevin, PhD, and Bina Ain, RPH. Special thanks also to Eric Shooter, PhD, Professor Emeritus, Stanford University School of Medicine, Stanford, CA, USA. The authors have no conflicts of interest that are directly relevant to the content of this study.
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Darby, J.K., Pasta, D.J., Wilson, M.G. et al. Long-Term Therapeutic Drug Monitoring of Risperidone and Olanzapine Identifies Altered Steady-State Pharmacokinetics. Clin. Drug Investig. 28, 553–564 (2008). https://doi.org/10.2165/00044011-200828090-00002
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DOI: https://doi.org/10.2165/00044011-200828090-00002