AIMTo determine optimal sampling strategies to allow the calculation of clinical pharmacokinetic parameters for selected antipsychotic medicines using a pharmacometric approach.
METHODSThis study utilized previous population pharmacokinetic parameters of the antipsychotic medicines aripiprazole, clozapine, olanzapine, perphenazine, quetiapine, risperidone (including 9-OH risperidone) and ziprasidone. D-optimality was utilized to identify time points which accurately predicted the pharmacokinetic parameters (and expected error) of each drug at steady-state. A standard two stage population approach (STS) with MAP-Bayesian estimation was used to compare area under the concentration-time curves (AUC) generated from sparse optimal time points and rich extensive data. Monte Carlo Simulation (MCS) was used to simulate 1000 patients with population variability in pharmacokinetic parameters. Forward stepwise regression analysis was used to determine the most predictive time points of the AUC for each drug at steady-state.
RESULTSThree optimal sampling times were identified for each antipsychotic medicine. For aripiprazole, clozapine, olanzapine, perphenazine, risperidone, 9-OH risperidone, quetiapine and ziprasidone the CV% of the apparent clearance using optimal sampling strategies were 19.5, 8.6, 9.5, 13.5, 12.9, 10.0, 16.0 and 10.7, respectively. Using the MCS and linear regression approach to predict AUC, the recommended sampling windows were 16.5-17.5 h, 10-11 h, 23-24 h, 19-20 h, 16.5-17.5 h, 22.5-23.5 h, 5-6 h and 5.5-6.5 h, respectively.
CONCLUSIONThis analysis provides important sampling information for future population pharmacokinetic studies and clinical studies investigating the pharmacokinetics of antipsychotic medicines.
WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Antipsychotic medicines are widely prescribed for the management of schizophrenia. However there are high rates of discontinuation, drug switching and dose adjustment which in part is due to the large inter-individual variability in response to these medicines.• Pharmacometric approaches to determine pharmacokinetic parameters using sparse sampling strategies are increasing. However the optimal sampling time points which determine the precision and accuracy of these parameters are typically not taken into account.• Aside from clozapine, therapeutic drug monitoring strategies for other antipsychotic medicines are not implemented in hospital settings routinely and this is in part due to the lack of clearly defined exposure-response relationships.
WHAT THIS STUDY ADDS• This analysis has utilized pharmacometric tools to provide optimal sampling time points for future population PK/PD studies, guidance for therapeutic drug monitoring and to allow clinicians practical solutions to calculate complex pharmacokinetic parameters when interpreting exposure to antipsychotic medicines. • Bayesian population PK estimates using sparse but optimal time points yield excellent correlations and only small errors when compared with extensive sampling strategies.• Tr...