Olanzapine over dose
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olanzapine overdose toxicity management
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Olanzapine Overdose
Pharmacology Basis for Toxicity
Olanzapine is a second-generation (atypical) antipsychotic with activity at multiple receptor types: dopamine D₁/D₂, serotonin 5-HT₂, muscarinic M₁–M₅, histamine H₁, and α₁-adrenergic receptors. This broad receptor profile drives the clinical features seen in overdose. After oral ingestion, peak plasma levels occur within 1–6 hours; the drug has high protein binding and a large volume of distribution with primarily hepatic (CYP450) metabolism.
Toxicity Classification
| Parameter | Details |
|---|---|
| Overall toxicity | Moderate |
| Lethal dose | Unclear; fatal outcomes reported at acute doses as low as 450 mg (therapeutic dose is 5–20 mg/day) |
| Fatality risk alone | Low, but deaths have occurred |
The 450 mg fatal threshold is approximately 22–90× the standard daily dose, but individual susceptibility varies considerably.
— Maudsley Prescribing Guidelines in Psychiatry, 15th ed., Table 13.1
Clinical Features
CNS Effects
- Lethargy, sedation, confusion, delirium — most common; due to H₁ and M₁ antagonism
- Myoclonus — involuntary muscle jerks
- Coma in severe cases
- Paradoxical agitation (especially in mixed overdoses with antimuscarinic agents)
- Seizures — rare (~1% overall for antipsychotics; less common with olanzapine than clozapine/loxapine)
Cardiovascular Effects
- Sinus tachycardia — most common cardiovascular finding (α₁-blockade + antimuscarinic)
- QTc prolongation — possible; risk of torsades de pointes if QTc >500 ms
- Orthostatic hypotension — α₁-adrenergic antagonism
- Atrial fibrillation — reported in overdose cases (rare)
Metabolic / Muscular
- Myopathy / rhabdomyolysis — associated with acute muscle toxicity
- Hypothermia
- Antimuscarinic features: dry skin/mucous membranes, urinary retention, decreased bowel sounds, hyperthermia
Note: Despite antimuscarinic properties, miosis (not mydriasis) is frequently observed due to concurrent α-adrenergic antagonism.
— Tintinalli's Emergency Medicine, Chapter 180
Diagnosis
| Investigation | Rationale |
|---|---|
| ECG | Assess QTc and QRS width |
| Serum electrolytes, glucose, creatinine | Baseline metabolic status |
| CK / creatinine kinase | Rhabdomyolysis (myopathy) |
| Paracetamol and salicylate levels | Co-ingestants in all intentional overdoses |
| Pregnancy test | Women of childbearing age |
| Blood glucose | Altered conscious level |
| Urine myoglobin | If rhabdomyolysis suspected |
Management
Immediate Resuscitation (ABCs)
- Airway: Maintain; intubate if GCS low or respiratory depression
- Oxygen supplementation + continuous pulse oximetry
- IV access + cardiac monitoring
Gastrointestinal Decontamination
- Activated charcoal (1 g/kg) if patient presents within 1–2 hours of ingestion and airway is protected
- Gastric lavage only if massive ingestion and early presentation with secured airway
CNS Depression
- Assess blood glucose; consider naloxone (to exclude opioid co-ingestion) and thiamine
- Benzodiazepines (e.g., lorazepam) for seizures
Cardiovascular Support
| Problem | Treatment |
|---|---|
| Hypotension | IV crystalloid 1–2 L (adults); if persistent, use direct α-agonists (phenylephrine or norepinephrine). Avoid dopamine (indirect-acting, less effective with α-blockade) |
| QTc >500 ms | Magnesium sulfate 2 g IV over 10 min (regardless of serum Mg²⁺ level) |
| Torsades de pointes | Magnesium sulfate 2 g IV bolus + infusion 2–4 mg/min; overdrive pacing if refractory |
| QRS widening + ventricular dysrhythmia | Sodium bicarbonate 1–2 mEq/kg IV bolus; lidocaine as alternative |
| Avoid | Class Ia (quinidine, procainamide), Ic (propafenone), III (amiodarone), IV antiarrhythmics — may potentiate cardiotoxicity |
Rhabdomyolysis
- IV fluid resuscitation
- Monitor urine output; consider urinary alkalinisation if CK markedly elevated
Disposition
- Observe for at least 6 hours from time of ingestion
- Safe for discharge if after 6 hours: normal mental status, stable vitals, no orthostatic hypotension, normal QTc
- Admit to monitored bed if: sinus tachycardia, QT prolongation, or any toxicity signs
- ICU admission if: seizures, respiratory depression, refractory hypotension, acidosis, severe rhabdomyolysis
Special Considerations
- Olanzapine + samidorphan (Lybalvi) co-formulation: similar toxicity profile to olanzapine alone, but co-ingested opioids may be partially antagonised by samidorphan, altering opioid overdose risk
- Paediatric exposure: Even a single tablet can cause significant CNS and respiratory depression in young children
- Post-injection delirium/sedation syndrome (PDSS): Olanzapine long-acting injectable overdose requires ≥3 hours observation; signs are equivalent to oral overdose
- Tolerance: Patients on long-term olanzapine therapy develop sedation tolerance and may tolerate higher overdose doses than naïve individuals
Sources:
- Maudsley Prescribing Guidelines in Psychiatry, 15th ed., Table 13.1 (Psychotropics in Overdose)
- Tintinalli's Emergency Medicine: A Comprehensive Study Guide, Ch. 180 (Antipsychotics)
- Rosen's Emergency Medicine: Concepts and Clinical Practice, Ch. 150
Clinical note: In all cases of suspected olanzapine overdose, urgent referral to acute medical facilities is strongly advised. Contact your regional Poisons Information Centre for real-time guidance.
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