Risperidone: Drug Information
1. Drug Name
Generic Name
Risperidone
Brand Name(s)
- Pakistan: Rispaxol, Rispolept
- India: Risperdal, Riscalm
- US: Risperdal
- UK: Risperdal, Risperdal Consta (long-acting injectable)
2. Pharmacological Class
Class
Atypical antipsychotic
Subclass
Benzisoxazole derivative
3. Mechanism of Action
Risperidone acts by antagonizing dopamine D2 receptors and serotonin 5-HT2A receptors in the brain. It also has antagonistic effects on adrenergic alpha1 and histamine H1 receptors.
4. Indications
Primary Indications
- Schizophrenia: Treatment of schizophrenia, including both positive and negative symptoms.
- Bipolar disorder: Acute and maintenance treatment of manic or mixed episodes.
- Irritability associated with autistic disorder: Treatment of irritability in children and adolescents (5-16 years) with autistic disorder.
Off-label Uses
- Behavioral disorders in elderly patients with dementia
- Obsessive-compulsive disorder (OCD)
- Tourette syndrome
5. Dosage and Administration
Standard Dosage
For schizophrenia:
- Initial: 0.5-1 mg twice daily
- Maintenance: 2-8 mg/day
For bipolar disorder:
- Initial: 2-3 mg/day
- Maintenance: 1-6 mg/day
For autism-related irritability (children and adolescents):
- Initial: 0.5 mg/day
- Maintenance: 0.5-3 mg/day
Route of Administration
Oral (tablets), Oral solution, Long-acting injectable (Risperdal Consta)
Special Populations
- Pediatric: Safety and efficacy in children under 5 years of age have not been established.
- Geriatric: Use with caution due to increased risk of cerebrovascular adverse reactions.
6. Pharmacokinetics
Absorption
Rapidly absorbed after oral administration, with peak plasma concentrations reached within 1-2 hours.
Distribution
Extensively distributed throughout the body. Plasma protein binding is about 90%.
Metabolism
Metabolized in the liver by CYP2D6 and CYP3A4 enzymes to its major active metabolite, 9-hydroxyrisperidone.
Excretion
Excreted mainly in urine (70%) and feces (14%).
Half-life
Elimination half-life of risperidone is approximately 3 hours, and for 9-hydroxyrisperidone, it is 21 hours.
7. Contraindications
- Known hypersensitivity to risperidone or any components of the formulation
- Severe CNS depression or comatose states
- Concurrent use with a strong CYP3A4 inducer (e.g., rifampin)
8. Warnings and Precautions
- Increased mortality in elderly patients with dementia-related psychosis
- Neuroleptic malignant syndrome (NMS)
- Tardive dyskinesia
- Hyperglycemia and diabetes mellitus
- Orthostatic hypotension
9. Side Effects
Common Side Effects
- Drowsiness
- Weight gain
- Increased appetite
Serious Side Effects
- Extrapyramidal symptoms (EPS)
- Prolonged QT interval
- Seizures
10. Drug Interactions
Major Interactions
- Fluoxetine
- Carbamazepine
Moderate Interactions
- Antihypertensive agents
- Alcohol
Minor Interactions
- Caffeine
- Levodopa
11. Pregnancy and Lactation
Pregnancy Category
Category C - Risk cannot be ruled out.
Breastfeeding Considerations
Not recommended during breastfeeding due to potential adverse effects on the infant.
12. Patient Counseling Information
- Take as directed and do not exceed prescribed dose.
- Avoid activities requiring mental alertness until response to medication is known.
- Report any