What are the potential side effects of accidentally taking 1600mg of Seroquel (quetiapine)?

Accidental Seroquel 1600mg Overdose: Potential Side Effects

An accidental ingestion of 1600mg of quetiapine (Seroquel) represents a massive overdose—over 50 times the typical starting dose—and will likely cause severe sedation, cardiovascular instability with hypotension and tachycardia, potential loss of consciousness requiring airway protection, and possible cardiac conduction abnormalities including QT prolongation. 1

Immediate Life-Threatening Effects

Central Nervous System

• Profound drowsiness progressing rapidly to coma within 1.5-2.5 hours post-ingestion, requiring emergency intubation for airway protection 2, 3
• Loss of consciousness can occur suddenly and unexpectedly, even after initial alertness 3
• Seizures may occur, creating aspiration risk 1
• Dystonic reactions of the head and neck are possible, further complicating airway management 1

Cardiovascular Complications

• Severe hypotension due to alpha-adrenergic blockade, which is the primary mechanism of cardiovascular toxicity 1, 2
• Persistent tachycardia lasting 40-42 hours post-ingestion in documented cases 3
• QT interval prolongation with risk of torsades de pointes and life-threatening arrhythmias 1, 2
• First-degree heart block has been reported with overdoses of 9,600mg 1
• Circulatory collapse requiring aggressive fluid resuscitation and vasopressor support 1

Metabolic Disturbances

• Hypokalemia documented in overdose cases, which can further exacerbate cardiac arrhythmia risk 1

Documented Overdose Outcomes

Clinical trial data shows survival after ingestion of up to 30 grams (30,000mg) of quetiapine, though death has occurred with as little as 13.6 grams in one case 1. Post-marketing surveillance includes very rare reports of death or coma from quetiapine overdose alone 1.

In published case reports of overdoses exceeding 10,000mg, patients experienced:

• Rapid progression from alert to unresponsive within 1-2.5 hours 3
• Need for mechanical ventilation lasting 16+ hours 3
• Tachycardia persisting for approximately 40 hours 3
• Blood concentrations 6-16 times the therapeutic range in fatal cases 4

Critical Management Principles

Immediate Interventions Required

• Establish and maintain airway immediately—intubation should be performed early given the high risk of sudden deterioration in consciousness 1, 2
• Continuous cardiac monitoring with serial ECGs to detect arrhythmias and QT prolongation 1
• Gastric lavage after intubation if patient is unconscious, followed by activated charcoal with laxative 1

Cardiovascular Support

• Aggressive IV fluid resuscitation for hypotension 1, 5
• Avoid epinephrine and dopamine—beta-stimulation will worsen hypotension in the setting of quetiapine-induced alpha blockade 1
• If vasopressors are needed, use agents without beta-agonist activity 1
• Avoid disopyramide, procainamide, and quinidine if antiarrhythmic therapy is needed, as these carry theoretical risk of additive QT prolongation 1

Monitoring Duration

• Mandatory ICU admission for all quetiapine overdoses requiring hospitalization 2
• Close medical supervision until full recovery, which may take 40+ hours based on the prolonged tachycardia documented in overdose cases 3
• Serial electrolyte monitoring, particularly potassium 1

Pharmacokinetic Considerations

The terminal elimination half-life after massive overdose is approximately 22 hours (not the 6 hours cited in standard references), meaning toxic effects can persist for days 5. Peak serum concentrations may be lower than expected due to reduced absorption from the overdose itself or from activated charcoal administration 5.

Common Pitfalls to Avoid

• Do not assume initial alertness means safety—patients can deteriorate suddenly from awake to comatose within 1-2 hours 3
• Do not use standard vasopressors blindly—epinephrine and dopamine are contraindicated due to paradoxical worsening of hypotension 1
• Do not discharge early—cardiovascular effects, particularly tachycardia, can persist for 40+ hours 3
• Do not induce emesis—risk of aspiration is too high given the potential for rapid loss of consciousness and dystonic reactions 1