Adults

For Schizophrenia: Initial dose usually 0.5-2 mg once daily, gradually increased to target 4-6 mg/day. For Bipolar Mania: Initial dose usually 2-3 mg once daily, adjusted to 1-6 mg/day. For Autistic Irritability: Initial 0.25-0.5 mg once daily, adjusted based on response and tolerability.

Elderly

Lower initial doses (e.g., 0.5 mg twice daily) and slower titration are recommended for elderly patients, especially in those with renal or hepatic impairment.

Renal_impairment

For patients with severe renal impairment (creatinine clearance < 30 mL/min), initial dose should be 0.5 mg twice daily. Dose should be slowly titrated and should not exceed 1.5 mg twice daily.

Onset

Initial therapeutic effects may be observed within a few days to weeks, with full effect taking several weeks.

Excretion

Excreted primarily via urine (70%) and feces (14%).

Half life

Risperidone: approximately 3 hours; 9-hydroxyrisperidone (active metabolite): approximately 21 hours.

Absorption

Rapidly and almost completely absorbed from the gastrointestinal tract. Peak plasma concentrations are reached within 1-2 hours for risperidone and 3-6 hours for 9-hydroxyrisperidone (active metabolite).

Metabolism

Extensively metabolized in the liver, primarily via cytochrome P450 2D6 (CYP2D6) to 9-hydroxyrisperidone, which is equally active.

CNS Depressants

CNS depressants (e.g., alcohol, benzodiazepines, opioids): May have additive sedative effects. Use with caution.

Antihypertensives

Antihypertensives: May enhance hypotensive effects due to alpha-adrenergic blocking activity.

CYP2D6 Inhibitors

Potent CYP2D6 inhibitors (e.g., fluoxetine, paroxetine): May increase plasma concentrations of risperidone and its active metabolite. Dose adjustment may be necessary.