Model-Informed Clinical Development of Once-Every-6-Month Injection of Paliperidone Palmitate in Patients with Schizophrenia: A Pharmacometric Bridging Approach (Part I).

BACKGROUND AND OBJECTIVE: A model-informed drug development (MIDD) approach was implemented for paliperidone palmitate (PP) 6-month (PP6M) clinical development, using pharmacokinetics and pharmacokinetic/pharmacodynamic model-based simulations. METHODS: PP6M pharmacokinetics were simulated by extending the PP 3-month (PP3M) pharmacokinetic model to account for increased injection volume, and hence dose. Contribution of the MIDD approach to the design of the pivotal PP6M phase-3 study (PP6M/PP3M noninferiority study, NCT03345342) investigating schizophrenia relapse rates was twofold: (1) PP6M dose selection, and (2) hypothesis generation that lower trough concentrations (Ctrough) associated with PP6M, relative to PP3M, were not associated with lower efficacy, which was to be evaluated in the phase-3 study. Moreover, accompanied by an intense sampling scheme to adequately characterize paliperidone pharmacokinetics and to elucidate the potential relationship between concentration and safety/efficacy, the bridging strategy eliminated the need for additional phase-1/phase-2 clinical studies. RESULTS: Using a MIDD bridging strategy, PP6M doses were selected that, compared with PP3M, were expected to have a similar range of exposures and a noninferior relapse rate and safety profile. Clinical data from PP6M/PP3M noninferiority study confirmed that PP6M, compared with PP3M, had a similar range of exposures (T'jollyn et al. in Eur J Drug Metab Pharmacokinet 2024), as well as a noninferior relapse rate and safety profile (this manuscript). CONCLUSIONS: Consistency of the MIDD approach with observed clinical outcomes confirmed the hypothesis that lower Ctrough did not lead to increased relapse rates at the doses administered. Although higher paliperidone peak concentrations are achieved with corresponding doses of PP6M relative to PP3M in the phase-3 clinical study, types and incidences of treatment-related adverse events were comparable between PP6M and PP3M groups and no new safety concerns emerged for PP6M (Najarian et al. in Int J Neuropsychopharmacol 25(3):238-251, 2022).

Model-Informed Clinical Development of 6-Monthly Injection of Paliperidone Palmitate in Patients with Schizophrenia: Dosing Strategies Guided by Population Pharmacokinetic Modeling and Simulation (Part II).

BACKGROUND AND OBJECTIVE: Paliperidone palmitate 6-month (PP6M) intramuscular (IM) injection is the longest-acting treatment available for patients with schizophrenia. A population pharmacokinetic (popPK) modeling and simulation approach was deployed to inform dosing strategies for PP6M. METHODS: The extensive analysis database included 15,932 paliperidone samples from 700 patients receiving gluteal paliperidone palmitate 3-month (PP3M) or PP6M injections in the double-blind phase of a phase-3 noninferiority study (NCT03345342). Exposure parameters for paliperidone appeared to increase dose-proportionally within each dosing schedule (PP3M/PP6M). The range of paliperidone exposures after IM administration of PP6M overlaps with that of corresponding doses of oral paliperidone extended release, PP 1-month (PP1M), and PP3M. Model-based simulations were performed to investigate paliperidone exposures in different PP6M dosing scenarios and relevant subpopulations. RESULTS: A dosing window of ≤ 2 weeks earlier and ≤ 3 weeks later than the target 6-month interval for maintenance treatment with PP6M dosing maintains paliperidone exposures at levels that are not expected to substantially impact its safety and efficacy. For missed-dose scenarios, tailored re-initiation regimens are proposed that should be applied before resuming PP6M maintenance dosing. Regarding subpopulations, PP6M 700 mg eq. is the highest dose recommended in mild renal-impairment patients; the paliperidone pharmacokinetics after PP6M administration is not affected by sex, body mass index, or age in a clinically meaningful way. CONCLUSION: Paliperidone concentration-time profiles after PP6M and PP3M dosing were adequately described by the popPK model. Model-based simulation results provide guidance for clinicians on initiating PP6M therapy, transitioning between paliperidone formulations, the dosing windows to use for maintenance dosing, and managing missed PP6M doses.

Development of a physiologically-based pharmacokinetic model to simulate the pharmacokinetics of intramuscular antiretroviral drugs.

There is growing interest in the use of long-acting (LA) injectable drugs to improve treatment adherence. However, their long elimination half-life complicates the conduct of clinical trials. Physiologically-based pharmacokinetic (PBPK) modeling is a mathematical tool that allows to simulate unknown clinical scenarios for LA formulations. Thus, this work aimed to develop and verify a mechanistic intramuscular PBPK model. The framework describing the release of a LA drug from the depot was developed by including both the physiology of the injection site and the physicochemical properties of the drug. The framework was coded in Matlab® 2020a and implemented in our existing PBPK model for the verification step using clinical data for LA cabotegravir, rilpivirine, and paliperidone. The model was considered verified when the simulations were within twofold of observed data. Furthermore, a local sensitivity analysis was conducted to assess the impact of various factors relevant for the drug release from the depot on pharmacokinetics. The PBPK model was successfully verified since all predictions were within twofold of observed clinical data. Peak concentration, area under the concentration-time curve, and trough concentration were sensitive to media viscosity, drug solubility, drug density, and diffusion layer thickness. Additionally, inflammation was shown to impact the drug release from the depot. The developed framework correctly described the release and the drug disposition of LA formulations upon intramuscular administration. It can be implemented in PBPK models to address pharmacological questions related to the use of LA formulations.

Double-Controlled Release of Poorly Water-Soluble Paliperidone Palmitate from Self-Assembled Albumin-Oleic Acid Nanoparticles in PLGA in situ Forming Implant.

PURPOSE: To investigate the effects of solvents on the formation of self-assembled nanonization of albumin-oleic acid conjugates (AOCs) using a solvent exchange mechanism for the construction of in situ forming implants (ISFI). METHODS: A poorly water-soluble drug, paliperidone palmitate (PPP), was chosen as the model drug. AOC was synthesized with the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) reaction. Dichloromethane, tetrahydrofuran, ethanol, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and deionized water were selected to investigate the formation of self-assembled AOC nanoparticles (AONs). The volume ratios of organic solvents against water could determine the miscibility, injectability, and in situ nanonizing capability without aggregation. RESULTS: As the polarity of the organic solvents increased, the AONs exhibited a spherical shape, and the larger the volume of the solvent, the smaller the size of the AONs. To use AOC in ISFI for controlled release of PPP, poly(d,l-lactide-co-glycolide) (PLGA) was combined with the AOC in 2 mL of N-methyl-2-pyrrolidone and water solution (1.8/0.2 ratio). The release rates of all formulations exhibited similar curve patterns overall but were more controlled in decreasing order as follows: AOC, PLGA, and AOC/PLGA for 14 days. CONCLUSION: A combined formulation of AOC and PLGA was found to effectively control the initial burst release of the drug.

Impact of age and gender on paliperidone exposure in patients after administration of long-acting injectable formulations-an observational study using blood samples from 1223 patients.

PURPOSE: Paliperidone palmitate is an antipsychotic medication available as long-acting injectable (LAI) formulations. The aim of this study was to investigate the effect of age and gender on paliperidone exposure after administration of LAI formulations. METHODS: Data on serum concentrations of paliperidone from patients using LAI during were included retrospectively from a therapeutic drug monitoring (TDM) service. Information about dose was obtained from the requisition forms. As a measure of exposure, daily dose-adjusted serum concentration (C/D ratio) was used. Based on initial analysis of C/D ratios versus age, a breaking point close to 50 years was observed, thus deciding the grouping of patients as older (≥50 years) or younger (15-49 years). Linear mixed model analyses, allowing multiple measurements per patients, were used. RESULTS: In total, 1223 patients were included, whereof 1158 patients used paliperidone LAI in once-monthly intervals. In these patients (27.9% older), older patients had significantly higher paliperidone C/D ratio than younger patients (+20%, p<0.001). Compared to males, females had higher C/D ratio (+14%; p<0.001). Subsequently, older female users of once-monthly LAI intervals had 41% higher paliperidone C/D ratios compared to younger males (15.0 vs. 21.2 nM/mg; p<0.001). Compared to females aged 21-30 years, females with high age (≥70 years) had at least 105% higher paliperidone C/D ratio (p<0.001). CONCLUSION: The present study shows that older age and female gender are associated with higher paliperidone exposure than younger age and males, respectively. Particularly, older female patients (>50 years) are likely exposed to high concentration and cautious dosing in this subgroup is required.

Lack of Smoking Effects on Pharmacokinetics of Oral Paliperidone-analysis of a Naturalistic Therapeutic Drug Monitoring Sample.

INTRODUCTION: Major smoking effects have been reported for a series of psychotropic agents, mainly including substrates of CYP450 1A2, although smoking may also affect alternative metabolic pathways. To our knowledge, smoking effects on paliperidone pharmacokinetics have not been assessed yet. METHODS: We compared plasma concentrations of paliperidone as well as dose-corrected-plasma concentrations (C/D) from a naturalistic database between smokers and nonsmokers using nonparametrical tests, such as the Mann-Whitney U-test (MWU). Additionally, we compared light and heavy smokers with nonsmokers separately. RESULTS: Comparing 55 smokers with 37 nonsmokers treated with oral paliperidone, no differences in the percentage of females, age, body weight, body mass index, and daily paliperidone dose were reported (p=0.709 for χ2, p=0.26, p=0.38, p=0.67, and p=0.8 for MWU). No differences were detected in plasma concentrations or C/D values (p=0.50 and p=0.96 for MWU). Likewise, differences in daily dose, plasma concentrations, or C/D values were not significant between light smokers (n=17) and nonsmokers (p=0.61, p=0.81, and p=0.33 for MWU) or heavy smokers (n=22) and nonsmokers (p=0.874, p=0.38, and p=0.59; MWU in all cases). DISCUSSION: Paliperidone is not affected by smoking, and paliperidone dose-adjustments in smokers may not be necessary. This may be seen as an essential difference to risperidone, whose cytochrome-mediated metabolism might be affected by smoking.

Field-amplified sample injection in capillary zone electrophoresis for the pharmacokinetic research of trace risperidone and its major metabolite 9-hydroxyrisperidone in beagle dogs.

This article describes a method for the simultaneous quantitation of risperidone and its major metabolite, 9-hydroxyrisperidone, in beagle dog plasma by field-amplified sample injection in capillary zone electrophoresis. The separation was carried out at 25°C in a 48 cm × 75 µm fused-silica capillary with an applied voltage of 20 kV using 60 mM NaH2 PO4 buffer (pH 3.6). The detection wavelength was 280 nm. Clean-up and preconcentration of plasma samples were conducted by 96-well formatted liquid-liquid extraction. In this study, this stacking technique provided a sensitivity enhancement of approximately 158 to 188 fold compared with the same sample without stacking. The method was suitably validated with respect to stability, specificity, linearity, lower limit of quantitation, accuracy, precision, and extraction recovery. Calibration curves exhibited good linearity (r2  > 0.995) over a wide concentration range of 2.5 to 200 ng/mL for both risperidone and 9-hydroxyrisperidone. The intra- and interday precisions at the three quality control levels were less than 11.40%. The intra- and interday accuracies ranged from 87.90 to 107.17% for risperidone and from 88.43 to 105.92% for 9-hydroxyrisperidone. All validation data were within the required limits. In conclusion, the method developed was successfully applied to pharmacokinetic studies of risperidone and 9-hydroxyrisperidone in beagle dogs.

Modelling Age-Related Changes in the Pharmacokinetics of Risperidone and 9-Hydroxyrisperidone in Different CYP2D6 Phenotypes Using a Physiologically Based Pharmacokinetic Approach.

PURPOSE: Dose-optimization strategies for risperidone are gaining in importance, especially in the elderly. Based on the genetic polymorphism of cytochrome P 450 (CYP) 2D6 genetically and age-related changes cause differences in the pharmacokinetics of risperidone and 9-hydroxyrisperidone. The goal of the study was to develop physiologically based pharmacokinetic (PBPK) models for the elderly aged 65+ years. Additionally, CYP2D6 phenotyping using metabolic ratio were applied and different pharmacokinetic parameter for different age classes predicted. METHODS: Plasma concentrations of risperidone and 9-hydroxyrisperidone were used to phenotype 17 geriatric inpatients treated under naturalistic conditions. For this purpose, PBPK models were developed to examine age-related changes in the pharmacokinetics between CYP2D6 extensive metabolizer, intermediate metabolizer, poor metabolizer, (PM) and ultra-rapid metabolizer. RESULTS: PBPK-based metabolic ratio was able to predict different CYP2D6 phenotypes during steady-state. One inpatient was identified as a potential PM, showing a metabolic ratio of 3.39. About 88.2% of all predicted plasma concentrations of the inpatients were within the 2-fold error range. Overall, age-related changes of the pharmacokinetics in the elderly were mainly observed in Cmax and AUC. Comparing a population of young adults with the oldest-old, Cmax of risperidone increased with 24-44% and for 9-hydroxyrisperidone with 35-37%. CONCLUSIONS: Metabolic ratio combined with PBPK modelling can provide a powerful tool to identify potential CYP2D6 PM during therapeutic drug monitoring. Based on genetic, anatomical and physiological changes during aging, PBPK models ultimately support decision-making regarding dose-optimization strategies to ensure the best therapy for each patient over the age of 65 years.

Physiologically Based Pharmacokinetic Modelling to Describe the Pharmacokinetics of Risperidone and 9-Hydroxyrisperidone According to Cytochrome P450 2D6 Phenotypes.

BACKGROUND AND OBJECTIVES: The genetic polymorphism of cytochrome P450 (CYP) 2D6 is characterized by an excessive impact on positive and adverse drug reactions to antipsychotics, such as risperidone. Consequently, the pharmacokinetics of the drug and metabolite can be substantially altered and exhibit a high variability between the different phenotypes. The goal of this study was to develop a physiologically based pharmacokinetic (PBPK) model considering the CYP2D6 genetic polymorphism for risperidone and 9-hydroxyrisperidone (9-OH-RIS) taking CYP3A4 into account. Additionally, risperidone dose adjustments, which would compensate for genetically caused differences in the plasma concentrations of the active moiety (sum of risperidone and 9-OH-RIS) were calculated. METHODS: Based on available knowledge about risperidone, 9-OH-RIS, and relevant physiological changes according to different CYP2D6 phenotypes, several PBPK models were built. In addition, an initial model was further evaluated based on the plasma concentrations of risperidone and 9-OH-RIS from a single-dose study including 71 genotyped healthy volunteers treated with 1 mg of oral risperidone. RESULTS: PBPK models were able to accurately describe risperidone exposure after single-dose administration, especially in the concentration range ≥ 1 µg/L, illustrated by a minimal bias and a good precision. About 90.3% of all weighted residuals versus observed plasma concentrations ≥ 1 µg/L were in the ± 30% range. The risperidone/9-OH-RIS ratio increased progressively according to reduced CYP2D6 activity, resulting in a mean ratio of 4.96 for poor metabolizers. Simulations demonstrate that dose adjustment of the drug by - 25% for poor metabolizers and by - 10% for intermediate metabolizers results in a similar exposure to that of extensive metabolizers. Conversely, the risperidone/9-OH-RIS ratio can be used to determine the phenotype of individuals. CONCLUSION: PBPK modelling can provide a valuable tool to predict the pharmacokinetics of risperidone and 9-OH-RIS in healthy volunteers, according to the different CYP2D6 phenotypes taking CYP3A4 into account. These models are able to ultimately support decision-making regarding dose-optimization strategies, especially for subjects showing lower CYP2D6 activity.

Population Pharmacokinetics of Paliperidone Palmitate (Once-Monthly Formulation) in Japanese, Korean, and Taiwanese Patients With Schizophrenia.

The paliperidone pharmacokinetics after intramuscular administration of once-monthly paliperidone palmitate in Japanese patients were studied in 3 phase 1 studies and in 2 phase 3 studies performed in Japan, Korea, and Taiwan. These data (Japanese, n = 509; Korean, n = 31; Taiwanese, n = 47) were used to describe the paliperidone palmitate pharmacokinetics in Japanese, to compare with non-Japanese, and to validate the historical population pharmacokinetic (Pop-PK) model for paliperidone palmitate, developed using data from studies in patients with schizophrenia outside Japan. The final historical Pop-PK model, including all significant patient covariates of Japanese studies, was used to simulate paliperidone plasma concentration-time data using nonlinear mixed effects, followed by comparison with actual data. Visual predictive checks displayed considerable overlap between predicted and actual plasma concentrations; the majority of observations were within the 90% prediction interval. Japanese, Korean, and Taiwanese patients had comparable plasma concentrations. Covariate distributions demonstrated comparatively lower median body mass index in Japanese, Korean, and Taiwanese patients versus rest-of-world population. Prediction errors for the data set used for external validation were within cutoff values, confirming accuracy/precision of the model. Paliperidone pharmacokinetics were adequately predicted for Japanese studies using the historical Pop-PK model, confirming its robustness. Pharmacokinetics in Japanese, Korean, and Taiwanese patients with schizophrenia were comparable with rest-of-world population.

Need for Bioequivalence Standards that Reflect the Clinical Importance of the Complex Pharmacokinetics of Paliperidone Palmitate Long-Acting Injectable Suspension.

Paliperidone palmitate is a second generation antipsychotic, approved for the treatment of schizophrenia in the form of the long-acting injectable (LAI) products INVEGA SUSTENNA® (once monthly injection) and INVEGA TRINZA® (once every 3 months injection). Paliperidone palmitate dissolves slowly after deep intramuscular injection before being hydrolyzed to paliperidone and absorbed into the systemic circulation. The pharmacokinetic (PK) profile of the INVEGA SUSTENNA® formulation is biphasic, comprised of an initial relatively fast zero-order input, which allows rapid attainment of therapeutic concentrations without oral supplementation; and a subsequent maintained second-stage, first-order input, allowing for once monthly administration. Changes to the manufacturing processes can substantially alter the release characteristics of paliperidone palmitate LAI and consequently its PK profile. As an example, larger or smaller particle sizes of paliperidone palmitate can result in a delayed or accelerated release of paliperidone into the systemic circulation, respectively. Such changes are clinically relevant, as transient excursions above therapeutic plasma concentrations can be associated with an increased risk of adverse effects, including tachycardia, hypotension, QT prolongation, and extrapyramidal symptoms. Conversely, a delay in attaining therapeutic plasma concentrations of paliperidone on initiation of treatment, or a return to low plasma concentrations before the end of a dosing interval during repeated dosing, increases the risk of relapse. Given the integral relationship of the PK profile to the product's clinical effects, it is important to have bioequivalence standards that reflect the complexity of the paliperidone palmitate LAI PK profile if one is to consider therapeutic equivalence based on simple bioequivalence testing. Although both the EMA and U.S. FDA have product-specific guidelines to determine bioequivalence, their requirements differ substantially. In Canada, no LAI product-specific bioequivalence guidance exists for multiphasic medication delivery systems, and the recently revised Comparative Bioavailability Standards: Formulations Used for Systemic Effects guidance applies only to oral and non-injectable formulations. We recommend that new Canadian standards be developed for multiphasic and biphasic intramuscular / subcutaneous (IM/SC) products, including paliperidone palmitate LAI products, because, similar to modified-release oral dosage forms, a different PK profile in modified-release IM/SC products can result in clinically meaningful differences in safety, efficacy, and tolerability. To ensure bioequivalence for both newly initiated and switch patients, this paper proposes bioequivalence standards that could be adopted in Canada that include two studies, a multiple-dose cross-over study, and a single-dose study with partial AUC metrics.

Pharmacokinetic-Pharmacodynamic Characterization of Relapse Risk for Paliperidone Palmitate 1-Month and 3-Month Formulations.

BACKGROUND: Pharmacokinetic-pharmacodynamic (PK/PD) models were developed to describe the relationship between the time course of paliperidone plasma concentrations and the risk of relapse of schizophrenia symptoms following administration of paliperidone palmitate 1-month (PP1M) and 3-month (PP3M) long-acting injectables, and to identify relevant covariates for relapse and dropout events. METHODS: Patient data from two global phase 3, relapse prevention studies comparing PP3M to placebo (study A) and PP3M to PP1M (study B) were analyzed. Dropout and relapse data were assessed using survival analysis as two separate single time-to-event models. Baseline covariates included age, sex, race/country, duration of illness, previous hospitalizations, prior use of long-acting injectables and use of multiple (≥2) antipsychotics at screening. RESULTS: The PK/PD analysis data set included 305 patients who were randomized to receive PP3M or placebo in the double-blind phase of study A and 1002 patients randomized to receive PP3M or PP1M in the double-blind phase of study B. Risk of relapse decreased with increasing paliperidone concentrations for both PP1M and PP3M, while it appeared to increase in patients with higher number of previous hospitalizations and/or with higher prerandomization (trough) paliperidone concentration (study A), and in patients on concomitant benzodiazepine medication and/or at Japan centers (study B). These findings are reflective of different illness severity in the population and of differences in medical practice for Japanese patients. In model-based simulations, PP3M and PP1M displayed similar relapse rates over time. CONCLUSIONS: This PK/PD analysis confirmed that PP1M and PP3M provide comparable efficacy in terms of relapse prevention, and that PP3M is superior to placebo. The PK/PD models presented here may as well be applied to studies with similar designs as either study A or B.

Serum Concentration of Paliperidone Palmitate Administered Every 3 Weeks.

Schizophrenia, a disabling yet relatively common mental illness, is often controlled by antipsychotic drugs. However, long-term treatments are subject to non-adherence and consequent treatment failure. Non-adherence can be reduced by administration of slow-release drugs such as intramuscularly injected (IM) paliperidone palmitate. Considerable inter- and intra-individual variation in serum drug concentration exists, whose effect on clinical efficacy remains unclear. We report two cases of off-label use resulting in serum paliperidone levels greatly exceeding the recommended therapeutic window. A 20- and 31-year-old male were treated with 150 mg IM paliperidone palmitate/21 days. After one and two years, blood drug concentrations were 240 nmol/l and 610 nmol/l, respectively. Neither patient exhibited major adverse effects. Thus paliperidone serum levels greatly in excess of recommended targets can be well tolerated, although we urge caution with off-label use of paliperidone palmitate as it is not always the most appropriate way to achieve the control of schizophrenia.

Real-life persistence of long-acting injectable antipsychotics in schizophrenic patients: A retrospective observational study in France
.

OBJECTIVE: Antipsychotics exhibit different profiles of efficacy and safety in patients with schizophrenia. It has recently been reported that the risk of rehospitalization was the lowest with paliperidone palmitate (PP), a long-acting injectable (LAI), when compared with other LAIs (of zuclopenthixol, perphenazine, and olanzapine). We aimed to investigate whether treating patients with PP was also associated with improved real-life treatment persistence. MATERIALS AND METHODS: We conducted a retrospective observational study of the LAI antipsychotics (LAIAs) dispensed in French retail pharmacies. Treatment persistence was defined as the non-discontinuation of LAIAs for ≥ 5 months after LAIA initiation (and was also analyzed by Kaplan-Meier persistence curves). RESULTS: A total of 4,492 patients were included in the study. The persistence rate was significantly greater for LAI-PP (64.5%) than for either LAI haloperidol decanoate (HD) or LAI risperidone microspheres (R) (46.4% and 35.4%, respectively). Multivariate Cox analyses illustrated that LAIA initiation with HD or R significantly increased the risk of discontinuation when compared with PP. CONCLUSION: PP demonstrated a significantly higher persistence rate than HD or R. Moreover, LAIA initiation with HD or R significantly increased the risk of treatment discontinuation relative to PP. Further comparative studies are required to comprehensively determine whether PP has a better efficacy and/or safety profile than other LAIs.

Paliperidone extended-release in the short- and long-term treatment of schizophrenia.

Paliperidone is a second-generation antipsychotic drug belonging to the class of benzisoxasole derivatives. Paliperidone is the major active metabolite of risperidone (9-OH-risperidone) and, as such, is comparable to the latter in terms of pharmacodynamic properties. However, due to its peculiar characteristics, paliperidone may be particularly useful in the treatment of schizophrenic patients. In this critical review of the literature the efficacy and tolerability in the short- and in the long-term have been evaluated in patients with schizophrenia. Taking into account the tolerability and efficacy data, together with the use of innovative sustained-release formulation, with a peculiar pharmacokinetic profile that allows single daily administration, paliperidone can be considered a valid option both for the short and the long-term treatment of schizophrenia.

Physiologically Based Modeling Approach to Predict Dopamine D2 Receptor Occupancy of Antipsychotics in Brain: Translation From Rat to Human.

Receptor occupancy (RO) is a translational biomarker for assessing drug efficacy and safety. We aimed to apply a physiologically based pharmacokinetic (PBPK) modeling approach to predict the brain dopamine D2 RO time profiles of antipsychotics. Clozapine and risperidone were modeled together with their active metabolites, norclozapine and paliperidone, First, in PK-Sim a rat PBPK model was developed and optimized using literature plasma PK data. Then, blood-brain barrier parameters including the expression and efflux transport kinetics of P-glycoprotein were optimized using literature microdialysis data on brain extracellular fluid (brainECF), which were further adapted when translating the rat PBPK model into the human PBPK model. Based on the simulated drug and metabolite concentrations in brainECF, drug-D2 receptor binding kinetics (association and dissociation rates) were incorporated in MoBi to predict RO. From an extensive literature search, 32 plasma PK data sets (16 from rat and 16 from human studies) and 23 striatum RO data sets (13 from rat and 10 from human studies) were prepared and compared with the model predictions. The rat PBPK-RO model adequately predicted the plasma concentrations of the parent drugs and metabolites and the RO levels. The human PBPK-RO model also captured the plasma PK and RO levels despite the large interindividual and interstudy variability, although it tended to underestimate the plasma concentrations and RO measured at late time points after risperidone dosing. The developed human PBPK-RO model was successfully applied to predict the plasma PK and RO changes observed after risperidone dose reduction in a clinical trial in schizophrenic patients.

Clinical Pharmacokinetics of a Lipid-Based Formulation of Risperidone, VAL401: Analysis of a Single Dose in an Open-Label Trial of Late-Stage Cancer Patients.

BACKGROUND AND OBJECTIVES: A clinical trial was conducted to measure and analyse the pharmacokinetic parameters of a lipid formulation of risperidone, VAL401. The VAL401 formulation is designed to repurpose risperidone from an antipsychotic to an adenocarcinoma treatment, with the lipid formulation altering the cellular uptake of risperidone, thus enabling anticancer biology to be exhibited in preclinical testing. METHODS: This first human trial of VAL401 measured the concentrations of risperidone and its primary metabolite, 9-hydroxyrisperidone, in the blood of patients after treatment with a single 2-mg dose of VAL401. RESULTS: The trial provided information on differences in the pharmacokinetic profile of risperidone in VAL401 that may be caused by the formulation and/or the nature of the cancer patient population. VAL401 provided the following key pharmacokinetic parameters for the risperidone plasma concentration after a single 2-mg dose of VAL401, with results normalised to a dosage of 1 mg for comparison with literature values: Tmax, 2 h; Cmax, 8 ng/ml; half-life, 3.5 h; area under the plasma concentration-time curve from time zero to infinity (AUC0-∞), 58.2 ng h2/mL. CONCLUSIONS: Further comparisons of the pharmacokinetic parameters of risperidone and 9-hydroxyrisperidone in plasma of patients administered VAL401 and the corresponding parameters obtained from published data for conventionally formulated risperidone provide evidence for altered biological processing of VAL401 as compared to risperidone. The absolute values obtained provide support for future studies of VAL401 as a cancer treatment, as the Cmax demonstrates sufficient exposure to reach the concentrations seen during preclinical anticancer testing, yet the overall exposure to the active moiety supports the use of the safety and tolerability data from conventional risperidone during future clinical trials.

Rats and rabbits as pharmacokinetic screening tools for long acting intramuscular depots: case study with paliperidone palmitate suspension.

Development of prodrug of 9-hydroxyrisperidone (paliperidone) long-acting intramuscular injection has enabled delivery over four-week time period with improved compliance. The key aim of this work was to establish a reliable preclinical model which may potentially serve as a screening tool for judging the pharmacokinetics of paliperidone formulation(s) prior to human clinical work. Sparse sampling composite study was used in rats, (Wistar/Sprague-Dawley (SD; n = 10)) and a serial blood sampling study design was used in rabbits (n = 4). Animals received intramuscular injection of paliperidone palmitate in the thigh muscle at dose of 16 (rats) and 4.5 mg/kg (rabbits). Samples were drawn in rats (retro-orbital sinus) and rabbits (central ear artery) and were analysed for paliperidone using liquid chromatography-mass spectrometry/ mass spectrometry (LC-MS/MS) assay. The plasma data was subjected to pharmacokinetic analysis. Following intramuscular injection of depot formulation in Wistar/SD rats and rabbits, absorption of paliperidone was slow and gradual with median value of time to reach maximum concentration (Tmax) occurring on day 7. The exposures (i.e. area under the curve (AUC; 0-28) days) were 18,597, 21,865 and 18,120 ng.h/mL, in Wistar, SD and rabbits, respectively. The clearance was slow and supported long half-life (8-10 days). Either one of the two models can serve as a research tool for establishing pharmacokinetics of paliperidone formulation(s).

Paliperidone palmitate in short- and long-term treatment of schizophrenia.

Poor adherence to treatment remains a major problem in the management of patients with schizophrenia. In the 60s, first generation antipsychotics in depot formulation have been introduced on the market with the aim to improve adherence to therapy. However, the limited effectiveness on negative symptoms and the tendency to induce extrapyramidal side effects has limited their use. Currently there are five second-generation antipsychotic long-acting formulations and the use of these drugs has definitely changed perspective: they are no more restricted as compounds intended to improve compliance, but they can be considered first-line drugs with proven efficacy and good tolerability. In this narrative review the efficacy and tolerability of paliperidone palmitate, as well as the economic impact of the use of this particular molecule, have been evaluated in the short- and long-term treatment of schizophrenia. Taking into account the results of different studies, paliperidone, especially in his long-acting formulation, can be considered a viable and effective treatment for patients with schizophrenia, both in the short- and in the long term.