Tricyclic Antidepressant Toxicity

Last Updated on by FRCEM Intermediate

Overview:

  • TCAs are weak bases (pKa 8.5) that can cause life-threatening sodium channel toxicity
  • Ingestion of 15 mg/kg tricyclic antidepressants would be expected to result in serious, potentially life-threatening

Examinations

  • CVS – dry mucous membranes, tachycardia, hypertension -> hypotension -> cardiovascular collapse (arrhythmia), postural hypotension, dehydration
  • CNS – nystagmus, dizziness, agitation, decreases level of consciousness, unconscious/coma, seizures, increase in tone, clonus, tremor, hypereflexia, pupillary dilation, blurred vision
  • GI – N+V, abdominal pain, dry mouth, ileus
  • METABOLIC – severe metabolic acidosis, fever
  • GU – urinary retention
  • SKIN – flushed

Investigations

  • ABG – metabolic acidosis
  • ECG:
    -> sinus tachycardia
    -> PR prolongation
    -> RAD
    -> R wave > 3mm in aVR
    -> prolonged QT interval (>430ms)
    -> QRS prolongation (>100ms)
    -> VF/VT/asystole
    -> 2nd or 3rd HB
    -> RBBB
  • Bloods – renal impairmen

Management

  • Consider activated charcoal if the patient presents within 1 hour of ingesting a toxic dose. A second dose of charcoal should be considered after 1 – 2 hours in patients with features of toxicity.
  • In adults consider immediate administration of 50 – 100 mL of 8.4% sodium bicarbonate
    • Hypotension
    • Wide QRS or arrhythmias
    • Seizures
    • Metabolic acidosis
  • If metabolic acidosis persists despite correction of hypoxia and adequate fluid resuscitation, consider correction with intravenous sodium bicarbonate.
  • Agitation: Diazepam
  • Convulsions: Benzodiazepines.NB. Avoid phenytoin
  • If cardiotoxicity is unresponsive to the above consider the use of a lipid emulsion; 5 mL/kg of 20% Intralipid as an intravenous bolus followed by 0.25 – 0.5 mL/kg/min for 30 – 60 minutes, to an initial maximum of 500 mL.
  • All patients should be observed for at least 6 hours after ingestion.

 

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