Table of Contents
Introduction
Risperidone is an atypical antipsychotic medication used in schizophrenia, bipolar disorder, irritability associated with autism spectrum disorder, and other psychiatric conditions. It works mainly through antagonism of dopamine and serotonin receptors in the central nervous system. Compared with typical antipsychotics, risperidone has lower extrapyramidal toxicity at therapeutic doses because of its combined serotonin-dopamine antagonistic activity.
Mechanism of Action (Step-wise)
- Risperidone acts primarily as an antagonist at dopamine D2 receptors and serotonin 5-HT2A receptors.
- Dopamine D2 receptor blockade decreases excessive dopaminergic transmission in mesolimbic pathways.
- Reduction of mesolimbic dopamine activity improves positive symptoms such as hallucinations and delusions.
- Serotonin 5-HT2A receptor antagonism increases dopamine release in nigrostriatal pathways.
- Increased dopamine in nigrostriatal pathways reduces extrapyramidal side effects.
- Risperidone also blocks α1-adrenergic receptors.
- α1 receptor blockade causes vasodilation and orthostatic hypotension.
- Histamine H1 receptor antagonism contributes to sedation and weight gain.
- Risperidone has relatively mild anticholinergic activity compared with some other atypical antipsychotics.
- The drug helps regulate abnormal neurotransmitter activity involved in psychosis and mood disorders.
- The overall effect is improvement of psychotic symptoms, mood stabilization, and behavioral control.
A key exam point is that risperidone blocks dopamine D2 and serotonin 5-HT2A receptors to reduce psychotic symptoms while limiting extrapyramidal toxicity.
Pharmacokinetics
Risperidone is administered orally or as a long-acting injectable formulation. It is metabolized in the liver mainly by CYP2D6 into an active metabolite, paliperidone. Both risperidone and paliperidone contribute to therapeutic effects. Elimination occurs through urine and feces.
Clinical Uses
Risperidone is used in schizophrenia, bipolar mania, irritability associated with autism spectrum disorder, and behavioral disturbances. Long-acting injectable preparations are used for maintenance therapy in schizophrenia.
Adverse Effects
Common adverse effects include sedation, dizziness, orthostatic hypotension, weight gain, and hyperprolactinemia. At higher doses, extrapyramidal symptoms may occur because of increased dopamine blockade. Metabolic syndrome and QT prolongation may also occur in some patients.
Comparative Analysis
| Feature | Risperidone | Haloperidol | Quetiapine |
|---|---|---|---|
| Drug class | Atypical antipsychotic | Typical antipsychotic | Atypical antipsychotic |
| Main receptors blocked | D2 + 5-HT2A | D2 | D2 + 5-HT2A |
| EPS risk | Moderate at high doses | High | Lower |
| Hyperprolactinemia | Common | Common | Less common |
| Sedation | Moderate | Mild | High |
| Weight gain | Moderate | Low | Moderate |
Risperidone differs from haloperidol because it additionally blocks serotonin 5-HT2A receptors, reducing extrapyramidal toxicity at standard doses. Compared with quetiapine, risperidone causes more hyperprolactinemia and slightly higher extrapyramidal risk.
MCQs
- Risperidone belongs to which drug class?
a) Typical antipsychotic
b) Atypical antipsychotic
c) Benzodiazepine
d) Antidepressant
Answer: b) Atypical antipsychotic
- Risperidone mainly blocks which dopamine receptor?
a) D1
b) D2
c) D3
d) D4
Answer: b) D2
- Risperidone also blocks which serotonin receptor?
a) 5-HT1A
b) 5-HT2A
c) 5-HT3
d) 5-HT4
Answer: b) 5-HT2A
- D2 blockade improves which symptoms of schizophrenia?
a) Negative symptoms only
b) Positive symptoms
c) Cognitive symptoms only
d) Motor symptoms only
Answer: b) Positive symptoms
- 5-HT2A antagonism helps reduce:
a) Gastric acid secretion
b) Extrapyramidal side effects
c) Calcium absorption
d) Blood glucose
Answer: b) Extrapyramidal side effects
- Risperidone blocks α1 receptors causing:
a) Hypertension
b) Orthostatic hypotension
c) Bronchospasm
d) Hyperglycemia
Answer: b) Orthostatic hypotension
- A common endocrine adverse effect is:
a) Hyperprolactinemia
b) Hypothyroidism
c) Hyperaldosteronism
d) Hypercalcemia
Answer: a) Hyperprolactinemia
- Risperidone is metabolized mainly by:
a) CYP3A4
b) CYP2D6
c) MAO
d) Xanthine oxidase
Answer: b) CYP2D6
- The active metabolite of risperidone is:
a) Olanzapine
b) Paliperidone
c) Clozapine
d) Haloperidol
Answer: b) Paliperidone
- Risperidone is commonly used in:
a) Schizophrenia
b) Hyperthyroidism
c) Peptic ulcer disease
d) Asthma
Answer: a) Schizophrenia
- Compared with haloperidol, risperidone generally causes:
a) Greater EPS at low doses
b) Lower EPS at therapeutic doses
c) No dopamine blockade
d) No sedation
Answer: b) Lower EPS at therapeutic doses
- A metabolic adverse effect associated with risperidone is:
a) Weight gain
b) Severe hypoglycemia
c) Hypernatremia
d) Cataracts
Answer: a) Weight gain
FAQs
What is the mechanism of action of risperidone?
Risperidone blocks dopamine D2 and serotonin 5-HT2A receptors in the CNS.
Why is risperidone considered an atypical antipsychotic?
Because it combines serotonin and dopamine antagonism with lower extrapyramidal toxicity than typical antipsychotics.
What is a common hormonal side effect of risperidone?
Hyperprolactinemia.
What conditions are treated with risperidone?
Schizophrenia, bipolar disorder, and irritability associated with autism.
How does risperidone reduce extrapyramidal symptoms?
By serotonin 5-HT2A antagonism increasing dopamine release in nigrostriatal pathways.
What is the active metabolite of risperidone?
Paliperidone.
References
Goodman & Gilman’s The Pharmacological Basis of Therapeutics – Antipsychotic Agents
https://accessmedicine.mhmedical.com/book.aspx?bookid=3191
Katzung: Basic and Clinical Pharmacology – Antipsychotic Drugs
https://accessmedicine.mhmedical.com/content.aspx?bookid=3382
Tripathi: Essentials of Medical Pharmacology – Antipsychotic Drugs
https://www.jaypeedigital.com
Harrison’s Principles of Internal Medicine – Schizophrenia and Bipolar Disorders
https://accessmedicine.mhmedical.com
