Development of a population pharmacokinetic model for the novel long-acting injectable antipsychotic risperidone ISM®

Population Pharmacokinetics of Risperidone and Paliperidone in Schizophrenia: A Systematic Review

Background: The primary treatment of schizophrenia is pharmacotherapy with antipsychotic agents, such as risperidone and paliperidone. Population pharmacokinetic (PopPK) modelling plays a crucial role in optimising therapy by predicting of plasma concentrations, therapeutic efficacy, and the risk of adverse effects using model informed precision dosing. Objectives: This systematic review examined the PopPK models of risperidone and paliperidone in patients diagnosed with schizophrenia based on the available scientific evidence. Methods: A systematic review of the health science databases was conducted. The inclusion criteria were original articles published in peer-reviewed journals, studies focusing on the development of original PopPK models of risperidone and paliperidone, and clinical studies. The exclusion criteria were full-text articles that could not be retrieved; studies not including subjects diagnosed with schizophrenia or schizoaffective disorders; and studies that did not investigate risperidone or paliperidone. Results: A total of 19 studies developing PopPK models were analysed, including one- or two-compartment PopPK model structures. Interindividual variability in the pharmacokinetic parameters was shown to be influenced by factors such as CYP2D6 activity, renal function, body mass index, and sex. Parameter estimation revealed high variability in clearance and volume of distribution. Conclusion: Numerous PopPK models for risperidone and paliperidone have been published with a detailed characterisation of absorption, metabolism, and elimination. Therefore, future research should focus on the external validation of these models to facilitate their integration into clinical practice and optimise individualised dosing, ultimately improving treatment efficacy and safety across diverse patient populations.

Pharmacokinetic characteristics of risperidone ISM for the treatment of schizophrenia

INTRODUCTION

Risperidone-ISM is a novel intramuscular long-acting injectable formulation (LAI) of risperidone approved for the treatment of schizophrenia in adults. Knowledge regarding the pharmacokinetic properties of risperidone-ISM can improve care.

AREAS COVERED

We assessed the pharmacokinetic properties of risperidone-ISM. Most importantly, risperidone-ISM achieves therapeutic blood levels within 12-48 h after the first injection without the need for overlapping oral cotreatment, loading dose, or booster injection. Second, the in-situ microparticle (ISM) technology achieves stable blood levels, allowing currently 1-monthly injections. Third, females and patients with higher body mass index may have lower risperidone-ISM clearance, translating into higher risperidone serum levels. Fourth, there are only minimal risperidone-ISM clearance differences between deltoid and gluteal injections that balance out at steady state. However, aspects including pharmacogenetic and drug-drug interactions involving risperidone-ISM would benefit from further clarification.

EXPERT OPINION

Risperidone-ISM achieves therapeutic blood levels within 12-48 h after a single injection, currently lasting for 1 month, easing the initiation of a LAI risperidone formulation in adults with schizophrenia where LAIs remain underutilized. Prescriptions of LAIs, including risperidone-ISM, are likely to increase with an improved understanding of pharmacokinetic profiles and patient acceptability and outcomes, including in real-world settings informing drug selection.

Exposure-Efficacy Analysis and Dopamine D2 Receptor Occupancy in Adults with Schizophrenia after Treatment with the Monthly Intramuscular Injectable Risperidone ISM

Dopamine D2 receptor occupancy (D2RO) significantly influences the clinical effectiveness and safety of many antipsychotic drugs. Maintaining a D2RO range of 65%-80% provides the best antipsychotic effects while minimizing adverse reactions. Data from a Phase III trial were used to establish an exposure-response relationship for monthly intramuscular Risperidone ISM (75 and 100 mg) or placebo administered to adults with schizophrenia. Pharmacodynamic analysis was based on an Emax model for Positive and Negative Syndrome Scale (PANSS) developed in NONMEM. Plasma concentrations of the active moiety were derived using a previously developed population pharmacokinetic model, which was used for D2RO simulations in conjunction with a published Emax model. The optimal D2RO range (65%-80%) was reached for the median within hours following the first injection of both Risperidone ISM doses. At steady state, median D2RO for both doses remained above 65% throughout the 28-day dosing period and demonstrated lower variability than oral risperidone. PANSS response did not differ significantly between dose groups, most likely because active moiety concentrations had already reached the plateau of the concentration-response relationship. The pharmacokinetic/pharmacodynamic analysis showed a profound placebo effect (-11.7%), and an additional maximal drug effect (-6.6%) resulting in a total PANSS improvement over time of -18.3%. Pharmacokinetic/pharmacodynamic modeling quantified a PANSS improvement over time after Risperidone ISM administration. The response was not significantly different in either dose group, likely because D2RO was already above the proposed efficacy threshold (65%) within 1 h after the first Risperidone ISM injection and remained above this level following repeated administrations.

Risperidone In Situ Microparticles: A Review in Schizophrenia

Risperidone in situ microparticles (risperidone ISM®) is a novel long-acting prolonged-release formulation approved in the EU and USA for treating schizophrenia in adults. Once-monthly intramuscular injections of risperidone ISM® provide immediate and sustained therapeutic levels of risperidone, eliminating the need for loading doses or oral supplementation. In the pivotal PRISMA-3 trial in patients with acute schizophrenia exacerbation, risperidone ISM® significantly improved Positive and Negative Syndrome Scale (primary endpoint) and Clinical Global Impression-Severity of Illness (key secondary endpoint) total scores over the 12-week double-blind phase, with improvements observed as early as day 8. Continued treatment sustained efficacy over the 12-month open-label extension phase. Risperidone ISM® also improved social functioning and had a positive impact on health-related quality of life. Patients stable on daily oral risperidone maintained their treatment benefits after switching to monthly risperidone ISM®. Risperidone ISM® was generally well tolerated in clinical trials, with a safety profile consistent with that of oral risperidone. Its fast onset of action, without the need for oral supplementation or loading doses, makes risperidone ISM® a promising long-acting injectable that could enhance treatment adherence.