What type of toxidrome is a quetiapine (antipsychotic medication) overdose considered?

Quetiapine Overdose Toxidrome Classification

Quetiapine overdose presents primarily as an anticholinergic toxidrome with sedative-hypnotic features and potential for QT prolongation.

Clinical Features of Quetiapine Toxidrome

Quetiapine, a second-generation (atypical) antipsychotic, produces a distinct pattern of symptoms in overdose that combines features of multiple toxidromes:

Primary Anticholinergic Features

• Central nervous system depression and altered mental status
  • Drowsiness (76% of cases) 1
  • Coma (10% of cases) 1
  • Delirium 2
• Cardiovascular effects
  • Sinus tachycardia (56% of cases) 1
  • QTc prolongation 2, 3
• Anticholinergic effects (responds to physostigmine) 4

Secondary Features

• Respiratory depression (5% of cases) 1
• Hypotension (18% of cases) 1
• Seizures (2% of cases) 1

Distinguishing Characteristics

What makes quetiapine overdose unique compared to other antipsychotics:

1. Higher risk of severe complications: Compared to other antipsychotics, quetiapine overdose is more likely to cause:

   • Hypotension (OR 2.05) 1
   • Coma (OR 2.16) 1
   • Respiratory depression (OR 2.49) 1
   • Need for intubation (OR 1.92) 1

2. QT prolongation mechanism: While quetiapine can prolong the QTc interval, this may be partly due to the tachycardia rather than direct cardiac effects 2. However, it is still considered a QT-prolonging medication that can potentially contribute to torsades de pointes in high doses 5.

3. Anticholinergic reversal: Unlike many other toxidromes, quetiapine-induced altered mental status has been shown to respond to physostigmine, confirming its anticholinergic properties 4.

Clinical Severity Predictors

The severity of quetiapine overdose correlates with:

• Reported ingested dose (doses >3g associated with ICU admission) 2
• Peak quetiapine concentration 2
• Glasgow Coma Scale score <15 2

Management Implications

Understanding this toxidrome guides management:

1. Airway management: Early intubation may be necessary due to rapid progression to coma and respiratory depression 3

2. Cardiovascular monitoring: Close monitoring for hypotension and QT prolongation is essential 5

3. Anticholinergic treatment: Consider physostigmine for severe altered mental status with anticholinergic features 4

4. Disposition planning: Patients with significant overdose (>3g) or altered mental status should be admitted to an ICU setting 3

Common Pitfalls

1. Underestimating severity: Quetiapine overdose can rapidly progress to severe toxicity requiring intubation 3

2. Misinterpreting QTc: The QTc prolongation may be overestimated due to tachycardia; consider the uncorrected QT interval as well 2

3. Missing anticholinergic features: Failure to recognize the anticholinergic component may lead to missed opportunities for targeted treatment with physostigmine 4

4. Drug interactions: Quetiapine toxicity may be worsened by co-ingestion of other medications that affect cytochrome P450 metabolism 5