Adults

Schizophrenia: Initial 25-50 mg BID, titrated up to 300-450 mg/day in 2-3 divided doses. Bipolar Mania: Initial 100 mg/day (Day 1), 200 mg/day (Day 2), titrated up to 400-800 mg/day. Bipolar Depression: Initial 50 mg at bedtime (Day 1), 100 mg (Day 2), 200 mg (Day 3), 300 mg (Day 4). Major Depressive Disorder (Adjunctive): Initial 50 mg/day, titrated up to 150-300 mg/day.

Elderly

Lower starting doses (e.g., 25 mg/day) and slower titration are recommended due to potential for reduced clearance and increased sensitivity. Maximize dose slowly.

Renal_impairment

No dosage adjustment is needed for mild to moderate renal impairment. For severe impairment, initiate with 25 mg/day and titrate cautiously.

Onset

Antipsychotic effects may take days to weeks to manifest fully. Sedative effects, however, can be noticeable shortly after the first dose.

Excretion

Approximately 73% of the dose is excreted in the urine and 20% in the feces, predominantly as inactive metabolites.

Half life

The elimination half-life is approximately 6-7 hours for quetiapine and 10-12 hours for its active metabolite, norquetiapine.

Absorption

Rapidly absorbed after oral administration. Peak plasma concentrations are typically reached within 1.5 hours. Food can increase Cmax and AUC.

Metabolism

Primarily metabolized in the liver, mainly by the cytochrome P450 3A4 (CYP3A4) enzyme, to various inactive metabolites and the active metabolite norquetiapine.

CNS Depressants

e.g., Alcohol, Benzodiazepines. Increased risk of sedation and central nervous system depression.

QT Prolonging Drugs

Concomitant use with drugs known to prolong the QT interval may increase the risk of cardiac arrhythmias. Caution is advised.

Potent CYP3A4 Inducers

e.g., Phenytoin, Carbamazepine, Rifampin. Concomitant use significantly decreases quetiapine plasma levels, reducing efficacy. Dose adjustment of quetiapine may be necessary.

Potent CYP3A4 Inhibitors

e.g., Ketoconazole, Erythromycin, Protease Inhibitors. Concomitant use significantly increases quetiapine plasma levels, increasing the risk of adverse effects. Concomitant use is contraindicated.