Quetiapine: Drug Information
1. Drug Name
Generic Name
Quetiapine
Brand Name(s)
- Pakistan: Seroquel
- India: Qutipin, Seroquel
- US: Seroquel, Seroquel XR
- UK: Seroquel, Seroquel XL
2. Pharmacological Class
Class
Atypical antipsychotic
Subclass
Dibenzothiazepine derivative
3. Mechanism of Action
Quetiapine acts by antagonizing multiple neurotransmitter receptors in the brain, including serotonin 5-HT2 and dopamine D2 receptors, contributing to its antipsychotic effects. It also has affinity for histamine H1 and adrenergic alpha1 receptors.
4. Indications
Primary Indications
- Schizophrenia: Treatment of schizophrenia and maintenance therapy to prevent relapse.
- Bipolar Disorder: Acute treatment of manic or mixed episodes, depressive episodes, and maintenance therapy for bipolar I disorder.
- Major Depressive Disorder (MDD): Adjunctive therapy in patients with major depressive disorder.
Off-label Uses
- Generalized Anxiety Disorder (GAD)
- Post-traumatic Stress Disorder (PTSD)
- Insomnia
5. Dosage and Administration
Standard Dosage
For schizophrenia:
- Initial: 25 mg twice daily
- Maintenance: 150-750 mg/day
For bipolar disorder:
- Initial: 50 mg twice daily
- Maintenance: 200-800 mg/day
For major depressive disorder (adjunctive):
- Initial: 50 mg once daily
- Maintenance: 150-300 mg/day
Route of Administration
Oral (tablets, extended-release tablets)
Special Populations
- Pediatric: Safety and efficacy in children under 10 years of age have not been established.
- Geriatric: Use with caution due to increased risk of cerebrovascular adverse reactions.
6. Pharmacokinetics
Absorption
Rapidly absorbed with peak plasma concentrations reached within 1.5 hours for immediate-release and 6 hours for extended-release formulations.
Distribution
Widely distributed in the body, with about 83% bound to plasma proteins.
Metabolism
Metabolized primarily in the liver by CYP3A4 enzyme to its active metabolite, norquetiapine.
Excretion
Excreted mainly in urine (73%) and feces (21%).
Half-life
The elimination half-life of quetiapine is approximately 7 hours, and for norquetiapine, it is about 12 hours.
7. Contraindications
- Known hypersensitivity to quetiapine or any components of the formulation
- Concurrent use with strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole)
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
- Dizziness
- Dry mouth
- Weight gain
Serious Side Effects
- Extrapyramidal symptoms (EPS)
- Hyperglycemia
- Seizures
10. Drug Interactions
Major Interactions
- Ketoconazole
- Ritonavir
Moderate Interactions
- Antihypertensive agents
- Phenytoin
Minor Interactions
- Alcohol
- St. John's Wort
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 alcohol and be cautious with activities requiring mental alertness until the response to the medication is known.
- Monitor for signs of high blood sugar (e.g., increased thirst, urination) and report to the healthcare provider.
- Maintain a balanced diet and regular exercise to manage weight gain.