Antipsychotic toxicity

Background

• Isolated overdose of antipsychotics is rarely fatal
• Toxicity results in blockade of some or all of the following receptors:
  • Dopamine - extrapyramidal symptoms
  • Alpha-1 - orthostatic hypotension, reflex tachycardia
  • Muscarinic - anticholinergic symptoms
  • Histamine - sedation

Clinical Features

1. Extrapyramidal
   1. Acute dystonia
      1. Tongue protrusion, facial grimacing, trismus, oculogyric crisis
   2. Akathisia
2. CNS
   1. Lethargy, ataxia, dyarthria, confusion, coma
   2. Seizure (1%)
3. Anticholinergic Effects
   1. Tachycardia, dry mucous membranes, dry skin, decreased bowel sounds, delirium
4. ECG changes
   1. Sinus tachycardia
   2. QT prolongation

Differential Diagnosis

Anticholinergic toxicity Causes

• Medications
  • Atropine
    • Lomotil toxicity
  • Antihistamines
  • Antidepressants
    • Tricyclic antidepressant (TCA) toxicity
    • Selective serotonin reuptake inhibitor toxicity
  • Antipsychotics
  • Muscle relaxants
  • Anti-Parkinsonians
• Plants
  • Jimson weed (Devil's trumpet)
  • Amanita mushroom

Treatment

1. Supportive
   1. Hypotension
      1. IVF
      2. Norepinephrine
   2. QT prolongation
      1. Treat all pts w/ QTc >500ms w/ magnesium 2-4gm IV over 10min
2. Extrapyramidal
   1. Diphenhydramine 25-50mg IV/IM OR benztropine 1-2mg IV/IM
   2. Oral therapy with either of above meds should be continued for 2 weeks

Disposition

• Consider discharge after 6hr as long as there are all of the following:
  • No mental status changes
  • Normal HR/BP
  • No orthostatic hypotension
  • Normal QT interval

See Also

• Neuroleptic Malignant Syndrome (NMS)
• Beta-Blocker Toxicity
• Calcium Channel Blocker Toxicity

Source

• Tintinalli