Risperidone in situ microparticles in psychiatric emergency settings: pharmacokinetic rationale, clinical evidence and practical implications

Introduction

Emergency departments are critical transition points for people with schizophrenia presenting with acute relapse, agitation or treatment discontinuation. Initiation of long‑acting injectable antipsychotics (LAIA) in this setting is often postponed because many formulations require oral supplementation or there is a delay in reaching therapeutic plasma levels. Furthermore, there remains a persistent perception that LAIA are intended solely for maintenance treatment and not for acute phases of illness. Additional barriers include diagnostic uncertainty, difficulty confirming prior oral tolerability, impaired decision‑making capacity during acute presentations and logistical constraints in emergency workflows. Risperidone in situ microparticles (ISM), a once‑monthly intramuscular dopamine D2 receptor antagonist formulation, may address part of this gap through its combined rapid and sustained release profile.

Aims

To review the existing scientific evidence supporting the potential use of risperidone ISM in psychiatric emergency settings, integrating pharmacokinetic data and results from clinical trials.

Methods

A narrative review was conducted using PubMed, the European Medicines Agency product information and published clinical studies on risperidone ISM, focusing on pharmacokinetics, onset of clinical effect, need for oral supplementation, acute relapse outcomes, tolerability and operational implications for emergency pathways. Reported inferential statistics were extracted from pivotal and real‑world studies.

Results

Regulatory pharmacokinetic data show that, after intramuscular administration, risperidone ISM provides an initial release at the time of injection, followed by depot‑mediated sustained exposure over the 28‑day dosing interval. Active moiety concentrations are detectable within 2 hours (13 ± 9 ng/mL for 75 mg; 29 ± 13 ng/mL for 100 mg), with therapeutic levels maintained at one month. This biphasic profile ensures dopamine D2 receptor occupancy above 65%, a recognised threshold for antipsychotic efficacy, without the need for loading doses or oral supplementation. In the pivotal randomised, double‑blind, placebo‑controlled trial, both 75 mg and 100 mg doses produced significantly greater improvement than placebo in Positive and Negative Syndrome Scale total score at day 85 (least‑squares mean differences −13.0 and −13.3; both p < 0.0001), with parallel improvements in Clinical Global Impression‑Severity. Real‑world evidence from a prospective study of 275 hospitalised patients with acute schizophrenia relapse demonstrated significant reductions in CGI‑S and PANSS‑6 as early as day 8, functional gains by day 28 and a median discharge at 8 days after the first injection. Treatment satisfaction reached 78%, and only 4% discontinued due to related adverse events.

Conclusions

The rapid attainment of therapeutic plasma concentrations, absence of oral overlap and once‑monthly coverage make risperidone ISM a plausible option for selected emergency department patients with schizophrenia relapse, particularly when non‑adherence or loss to follow‑up is anticipated. Its role is not as an acute sedative or substitute for immediate behavioural and medical stabilisation, but as an early continuity‑of‑care intervention once diagnosis, capacity, tolerability, consent and contraindications have been assessed. Dedicated emergency department studies are needed to evaluate patient selection, feasibility, safety and downstream outcomes.

References

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