Risperidone exerts its therapeutic effects through its action on multiple neurotransmitter systems in the brain. Its key mechanisms include:

1. Dopamine Receptor Antagonism:
   • Risperidone primarily blocks dopamine D2 receptors in the mesolimbic pathway, reducing positive symptoms of schizophrenia such as hallucinations and delusions.
   • It has a lower affinity for D2 receptors compared to first-generation antipsychotics, which contributes to its reduced risk of extrapyramidal side effects (EPS) at lower doses.
2. Serotonin Receptor Antagonism:
   • Risperidone strongly blocks serotonin 5-HT2A receptors, which is thought to improve negative symptoms (e.g., social withdrawal, apathy) and cognitive symptoms of schizophrenia.
   • This action also contributes to its efficacy in mood stabilization.
3. Other Receptor Interactions:
   • Risperidone has affinity for adrenergic α1 and α2 receptors, histamine H1 receptors, and muscarinic M1 receptors, which contributes to its side effect profile (e.g., sedation, orthostatic hypotension).
4. Mood Stabilization:

By modulating dopamine and serotonin activity, risperidone helps stabilize mood in bipolar disorder, particularly in manic or mixed episodes

Risperidone is approved for a variety of clinical conditions, including:

1. Schizophrenia:
   • Treatment of acute and chronic schizophrenia, including both positive and negative symptoms.
2. Bipolar Disorder:
   • Management of acute manic or mixed episodes.
   • Maintenance treatment to prevent recurrence of manic or depressive episodes.
3. Irritability Associated with Autism:
   • Treatment of irritability, aggression, and self-injurious behavior in children and adolescents with autism spectrum disorder (ASD).
4. Other Uses:
   • Behavioral and psychological symptoms of dementia (BPSD) (off-label use, with caution due to increased mortality risk in elderly patients).
   • Treatment-resistant depression (adjunctive therapy).

The dosage of risperidone varies depending on the indication, patient age, and clinical response. The following dosing guidelines are based on the British National Formulary (BNF) and clinical pharmacology references:

1. Schizophrenia:
   • Adults: Start with 1–2 mg once daily, increasing gradually to a maintenance dose of 4–6 mg daily.
   • Elderly: Lower starting doses (0.5 mg once or twice daily) are recommended due to increased sensitivity to side effects.
2. Bipolar Disorder:
   • Adults: Start with 2–3 mg once daily, adjusted based on response. The maintenance dose is typically 1–6 mg daily.
3. Irritability Associated with Autism:
   • Children and Adolescents: Start with 0.25 mg daily (for weight <20 kg) or 0.5 mg daily (for weight ≥20 kg), increasing gradually to a maximum of 1–3 mg daily.

Important Considerations:

• Risperidone is available in oral tablets, orally disintegrating tablets, and long-acting injectable (LAI) formulations.
• Dose adjustments may be necessary for patients with hepatic or renal impairment.
• Regular monitoring of weight, blood glucose, and lipid levels is recommended due to the risk of metabolic side effects.

Risperidone is associated with a range of side effects, some of which can be serious. Common side effects include:

1. Metabolic Effects:
   • Weight gain, hyperglycemia, and dyslipidemia, which increase the risk of metabolic syndrome and type 2 diabetes.
2. Central Nervous System:
   • Sedation, dizziness, and somnolence.
   • Extrapyramidal symptoms (EPS), including akathisia, dystonia, and parkinsonism, particularly at higher doses.
3. Cardiovascular:
   • Orthostatic hypotension and tachycardia.
4. Endocrine:
   • Elevated prolactin levels, leading to gynecomastia, galactorrhea, or menstrual irregularities.
5. Other:
   • Dry mouth, constipation, and increased appetite.

Serious Side Effects:

• Neuroleptic Malignant Syndrome (NMS): A rare but life-threatening condition characterized by fever, muscle rigidity, and autonomic instability.
• Tardive Dyskinesia: A potentially irreversible movement disorder associated with long-term use of antipsychotics.
• Increased Mortality in Elderly Patients with Dementia: Risperidone is associated with an increased risk of stroke and death in elderly patients with dementia-related psychosis.

Risperidone requires careful monitoring and adherence to specific precautions to ensure patient safety:

1. Metabolic Monitoring:
   • Regular monitoring of weight, blood glucose, and lipid levels is essential to detect and manage metabolic side effects.
2. Pregnancy and Lactation:
   • Risperidone should be used during pregnancy only if the potential benefits outweigh the risks. It is excreted in breast milk, so breastfeeding is generally not recommended.
3. Elderly Patients:
   • Lower doses are recommended due to increased sensitivity to side effects, particularly sedation and orthostatic hypotension.
4. Cardiovascular Risk:
   • Use with caution in patients with a history of cardiovascular disease or risk factors for QT prolongation.
5. Suicidal Risk:
   • Monitor for worsening depression or suicidal thoughts, particularly in patients with mood disorders.

Risperidone has a moderate potential for drug interactions due to its metabolism via cytochrome P450 enzymes (primarily CYP2D6). Key interactions include:

1. CYP2D6 Inhibitors:
   • Fluoxetine and paroxetine can increase risperidone levels, increasing the risk of side effects.
2. CYP2D6 Inducers:
   • Carbamazepine and rifampin can decrease risperidone levels, reducing its efficacy.
3. Central Nervous System Depressants:
   • Alcohol, benzodiazepines, and opioids can enhance sedation and respiratory depression.
4. Antihypertensives:
   • Risperidone may enhance the hypotensive effects of antihypertensive medications.
5. Other Interactions:
   • Levodopa and dopamine agonists: Reduced efficacy due to dopamine receptor antagonism.

Risperidone is the generic name for this medication. It is marketed under various brand names, depending on the country and manufacturer. Some examples include:

• Risperdal (a well-known brand in the United States and other regions).
• Risnia.
• Risperin.

Risperax