Active Ingredient

Seroquel contains the active ingredient quetiapine fumarate. It is an atypical antipsychotic used mainly for the treatment of schizophrenia and bipolar disorder. Quetiapine acts by modulating neurotransmitters in the brain, primarily serotonin and dopamine.

Indications for Use

Seroquel is indicated for the treatment of schizophrenia in adults and adolescents aged 13-17 years. It is also used for the treatment of bipolar I disorder, including manic and depressive episodes. Additionally, Seroquel can be prescribed for the maintenance treatment of bipolar disorder to prevent recurrence of mood episodes.

Dosage Forms

Seroquel is available in tablet form, typically in doses of 25 mg, 50 mg, 100 mg, 200 mg, 300 mg, and 400 mg. The extended-release variant, Seroquel XR, comes in doses of 50 mg, 150 mg, 200 mg, 300 mg, and 400 mg. Tablets should be taken orally with or without food.

Administration Guide

Seroquel should be taken exactly as prescribed by a healthcare professional. Dosage may start low and gradually increase based on individual response and tolerability. Do not crush, chew, or split extended-release tablets. Taking the medication at the same time each day can enhance adherence.

Initial Dosing

For schizophrenia, the initial dose is generally 25 mg twice daily. The dose may be increased in increments to a target range of 300-400 mg daily in divided doses. For bipolar mania, the starting dose is usually 50 mg twice daily, with increases to 200 mg by Day 4.

Maintenance Dosing

Maintenance dosing for schizophrenia may range from 150 mg to 750 mg daily, based on clinical response. For bipolar disorder, maintenance doses range from 400 mg to 800 mg daily. Dose adjustments may be necessary for elderly patients or those with hepatic impairment.

Mechanism of Action

Quetiapine, the active component in Seroquel, selectively antagonizes various neurotransmitter receptors. It primarily antagonizes serotonin 5-HT2A and dopamine D2 receptors, contributing to its therapeutic effects in mood and psychotic disorders. Quetiapine also exhibits affinity for histaminergic and adrenergic receptors.

Pharmacokinetics

Quetiapine is rapidly absorbed after oral administration, reaching peak plasma concentrations approximately 1.5 hours post-dose. The bioavailability is around 9%, which can be affected by food intake. Quetiapine has a half-life of approximately 7 hours, and its clearance is primarily hepatic, involving the cytochrome P450 enzyme CYP3A4.

Metabolism

Quetiapine undergoes extensive hepatic metabolism, generating several metabolites. The major active metabolite, norquetiapine, contributes to its pharmacological activity. It is essential to consider potential drug interactions that involve CYP3A4 inhibitors or inducers when prescribing Seroquel.

Drug Interactions

Seroquel may interact with a range of medications. Potent CYP3A4 inhibitors (e.g., ketoconazole, ritonavir) can increase quetiapine plasma levels, necessitating dose adjustments. Conversely, CYP3A4 inducers (e.g., phenytoin, carbamazepine) can decrease quetiapine levels, potentially reducing efficacy. Caution is advised when combining Seroquel with other central nervous system depressants.

Food Interactions

Food does not significantly affect the absorption of quetiapine, although it may delay the time to reach peak plasma concentration. It is recommended to consistently take Seroquel with or without food, based on the individual patient’s routine to maintain steady drug levels.

Adverse Effects

Common adverse effects include somnolence, dizziness, dry mouth, constipation, and weight gain. Orthostatic hypotension may occur, particularly during the initial dose-titration period. Some patients might experience metabolic changes such as increased cholesterol and blood glucose levels. Monitoring is recommended for these parameters.

Serious Adverse Reactions

Serious adverse reactions include neuroleptic malignant syndrome, tardive dyskinesia, and severe hypersensitivity reactions. Although rare, prolonged use can lead to increased risks such as cataracts and hyperglycemia. Regular follow-up and patient education on recognizing symptoms are vital for management.

Special Populations

Seroquel’s safety and efficacy in pediatric populations under 10 years of age have not been established. In elderly patients, caution is advised due to the risk of excessive sedation and orthostatic hypotension. Dose adjustments are necessary in patients with hepatic impairment, and the lowest effective dose should be used.

Monitoring and Follow-Up

Regular monitoring of blood pressure, weight, fasting plasma glucose, and lipid profiles is recommended during Seroquel treatment. Periodic assessment of mental status, symptom control, and side effect profile should be conducted to tailor the dosing regimen to individual needs.