Overview
Quetiapine is an atypical antipsychotic medication used primarily for the treatment of schizophrenia, bipolar disorder, and as adjunctive therapy for major depressive disorder. It works by modulating multiple neurotransmitter systems including dopamine and serotonin receptors. The drug requires careful monitoring due to potential metabolic effects, sedation, and other safety considerations.
Mechanism of Action
Quetiapine and its active metabolite norquetiapine act as antagonists at multiple neurotransmitter receptors including dopamine D1 and D2, serotonin 5-HT1A and 5-HT2A, histamine H1, muscarinic M1, and adrenergic α1 and α2 receptors. This broad receptor profile contributes to its antipsychotic, mood-stabilizing, and antidepressant effects while also causing side effects like sedation and metabolic changes.
Indications
- Treatment of schizophrenia
- Acute treatment of manic episodes associated with bipolar I disorder
- Acute treatment of depressive episodes associated with bipolar disorder
- Maintenance treatment of bipolar I disorder
- Adjunctive therapy for major depressive disorder
Common Doses
- 25 mg
- 50 mg
- 100 mg
- 150 mg
- 200 mg
- 300 mg
- 400 mg
Dosage
Dosage varies by indication: schizophrenia typically starts at 25 mg twice daily, titrated to 300-400 mg/day; bipolar mania starts at 50 mg twice daily, titrated to 400-800 mg/day; bipolar depression typically 50-300 mg/day; adjunctive MDD typically 150-300 mg/day. Extended-release formulations allow once-daily dosing.
Contraindications
- Hypersensitivity to quetiapine or any component of the formulation
- Concomitant use with strong CYP3A4 inhibitors in certain populations
- Patients with known QT prolongation or taking other QT-prolonging drugs
Side Effects
- Sedation/somnolence
- Dizziness
- Dry mouth
- Constipation
- Weight gain
- Increased appetite
- Dyspepsia
- Orthostatic hypotension
- Tachycardia
- Elevated liver enzymes
- Hyperglycemia
- Dyslipidemia
- Extrapyramidal symptoms
- Cataracts (requires monitoring)
Interactions
- Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole) increase quetiapine levels
- Strong CYP3A4 inducers (e.g., carbamazepine, phenytoin) decrease quetiapine levels
- Alcohol and CNS depressants increase sedation
- Antihypertensives may potentiate hypotension
- Other QT-prolonging drugs increase arrhythmia risk
Counseling Points
- Take as prescribed; do not stop abruptly due to withdrawal risk
- May cause significant drowsiness - avoid driving until effects known
- Rise slowly from sitting/lying position to prevent dizziness
- Monitor weight regularly and report significant changes
- Report any unusual movements, fever, or muscle stiffness immediately
- Regular eye exams recommended due to cataract risk
- Avoid alcohol and other sedating substances
- Take with or without food consistently