Management of Mirtazapine Overdose
Mirtazapine overdose is relatively benign and requires primarily supportive care with airway management, vital sign monitoring, and observation, as there are no specific antidotes available. 1, 2
Initial Assessment and Stabilization
Airway management is the first priority:
- Establish and maintain an open airway immediately 1
- Provide bag-mask ventilation if respiratory depression occurs 1
- Proceed to endotracheal intubation when clinically indicated 1
- Contact a regional poison center (1-800-222-1222) for expert guidance 1, 2
Vital sign monitoring with specific attention to:
- Heart rate (tachycardia occurs in approximately 33% of single-agent overdoses) 3
- Blood pressure (hypertension occurs in approximately 36% of cases) 3
- Obtain an ECG to evaluate for QT prolongation, though this is rare in isolated mirtazapine overdose 1, 2, 3
Expected Clinical Presentation
Mirtazapine overdose typically causes minimal acute toxicity:
- Patients ingesting approximately 10 times the therapeutic dose exhibit minimal symptoms 1, 4
- Common findings include drowsiness, disorientation, impaired memory, and mild CNS depression (GCS typically ≥10) 2, 3
- Tachycardia is the most common cardiovascular effect 2, 3
- Serious outcomes including seizures, serotonin toxicity, delirium, and arrhythmias are extremely rare in isolated mirtazapine overdose 3
Special Considerations for Co-Ingestions
Mixed overdoses significantly increase toxicity and require heightened vigilance:
- In suspected combined opioid and mirtazapine poisoning, administer naloxone first before other interventions 1
- Do not administer flumazenil if benzodiazepines may have been co-ingested, as this can precipitate seizures in benzodiazepine-dependent patients 1
- Co-ingestion with alcohol, benzodiazepines, or opioids results in more severe toxicity 1, 4
- QT prolongation and Torsades de Pointes have been reported in mixed overdoses at dosages higher than recommended 2
Treatment Approach
No specific antidotes exist for mirtazapine overdose:
- Management is entirely supportive 2
- Activated charcoal may be considered if presentation is within 1-2 hours of ingestion, though evidence is limited 4
- Most isolated mirtazapine overdoses require only short-term observation (approximately 6 hours for 10-fold overdoses, up to 14 hours median length of stay for larger ingestions) 4, 3
- ICU admission is typically not required for isolated mirtazapine overdose 3
Common Pitfalls to Avoid
Critical errors in management:
- Failing to recognize mixed overdoses, especially with opioids, benzodiazepines, or alcohol 1
- Administering flumazenil in potential benzodiazepine co-ingestion 1
- Over-aggressive intervention when isolated mirtazapine overdose is relatively benign 3
- Discharging patients before adequate observation period and psychiatric evaluation 4