Clinical effects: Acute: Drowsiness; Heart block (slow or irregular heartbeat); Hypotension (low blood pressure); Hypokalemia (weakness); Tachycardia (fast heartbeat).
Note: First degree heart block and hypokalemia were seen in one patient after an estimated overdose of 9600 mg of Quetiapine. Doses in excess of 10 g have been taken; Patients recovered without sequelae, and no fatalities were reported.
Treatment: Treatment is symptomatic and supportive.
To decrease absoprtion: Gastric lavage, following intubation in unconscious patients, and administration of Charcoal with a laxative should be considered. Induction of emesis is not recommended due to risk of aspiration if patient is oblunded or experiencing seizures or dystonic reactions of the head and neck.
Specific treatment: Administering antiarrhythmic therapy, if needed. However, Disopyramide, Procainamide, and Quinidine have the potential to add to the possible QT-interval - prolonging effects of Quetiapine overdosage. Also, Bretyllium may add to the hypotensive effect of Quetiapine, due to the additive alpha-adrenergic receptor blockade. Hypotension may be treated with intravenous fluids and/or sympathomimetic agents. However, Epinephrine and Dopamine may exacerbate hypotension through beta-adrenergic stimulation in the presence of Quetiapine-induced alpha-adrenergic receptor blockade.
Anticholinergic (antidyskinetic) medication should be administered in the presence of severe extrapyramidal symptoms.
Monitoring: Continuous electrocardiographic (ECG) monitoring is recommended to detect possible arrhythmias.
Supportive care: Establish and maintain airway and ensure adequate oxygenation and ventilation. Patients in whom intentional overdose is confirmed or suspected should be referred for psychiatric consultation.