Core Overview & Mechanism Risperidone is an atypical antipsychotic, classified as a serotonin-dopamine antagonist. Its primary efficacy arises from blocking dopamine D2 receptors, which targets the positive symptoms of schizophrenia, and blocking serotonin 5-HT2A receptors, which improves negative symptoms while lowering the risk of extrapyramidal symptoms (EPS) compared to conventional antipsychotics. It also antagonizes alpha-1 and H-1 histamine receptors, which can lead to orthostatic hypotension, sedation, and significant weight gain. The drug and its equally active major metabolite, 9-hydroxyrisperidone, are primarily metabolized by the CYP2D6 enzyme.

Boxed Warning Risperidone features a severe boxed warning for elderly patients with dementia-related psychosis, noting a significantly increased risk of morbidity, mortality (typically from heart failure or pneumonia), and cerebrovascular adverse events like stroke.

Indications & Standard Dosing Risperidone treats multiple psychiatric conditions, with varied maximum dosages:

• Schizophrenia: The adult oral target dose is 4 to 8 mg/day (Maximum: 16 mg/day).
• Bipolar I Disorder: The adult oral target is 1 to 6 mg/day (Maximum: 6 mg/day).
• Pediatric Uses: It is used to treat irritability in autistic disorder, moderate to severe Tourette's syndrome tics, disruptive behavioral disorders, and pediatric intensive care delirium.
• Organ Impairment: Patients with hepatic or renal impairment require a lowered starting oral dose (0.5 mg twice daily) and careful, gradual titration.

Formulations & Administration Protocols Risperidone's diverse administration routes dictate strict preparation and bridging protocols:

• Oral: Available as conventional tablets, orally-disintegrating tablets (ODT), and oral solutions.
• Intramuscular (IM) Depot: Risperdal Consta (gluteal/deltoid) and Rykindo (gluteal only) are dosed every 2 weeks (Maximum: 50 mg). Crucially, IM depots require oral risperidone supplementation during initiation to maintain therapeutic plasma levels (3 weeks for Consta, 1 week for Rykindo). Both involve rigorous reconstitution steps to suspend microspheres in diluent.
• Subcutaneous (SubQ) Depot: Perseris (monthly) and Uzedy (monthly or bi-monthly) are injected into the abdomen or upper arm. Unlike IM options, SubQ depots do not require oral dosing overlap because they provide clinically relevant concentrations immediately upon administration. Both require highly specific preparation steps, such as mixing liquid and powder syringes for 60 cycles (Perseris) or utilizing forceful downward arm flicks to properly position a viscous air bubble before injection (Uzedy).

Key Adverse Reactions & Pharmacokinetics Based on its D2 receptor binding profile, risperidone has a notably higher risk of causing hyperprolactinemia than most other atypical antipsychotics. Severe potential events include tardive dyskinesia, neuroleptic malignant syndrome (NMS), seizures, and suicidality. Moderate to mild side effects prominently include weight gain, pseudoparkinsonism, akathisia, and injection site reactions. Drug clearance relies heavily on renal excretion, with approximately 70% of an oral dose eliminated in the urine.