Tricyclic antidepressant toxicity

Background

  1. Serious toxicity is almost always seen within 6hr of ingestion
  2. Ingestion amount:
    1. <1mg/kg: Nontoxic
    2. >10mg/kg: Life-threatening
    3. >1gm: Commonly fatal
  3. Coingestants often increase severity of toxicity

Clinical Features

  1. Na Channel Blockade
    1. Negative inotropy, heart block, hypotension, ectopy
  2. Anti-Histamine Effects
    1. Sedation, coma
  3. Anti-Muscarinic Effects
    1. Central
      1. Agitation, delirium, confusion, hallucinations
      2. Slurred speech, ataxia
      3. Sedation, coma
      4. Seizures
    2. Peripheral
      1. Mydriasis, decreased secretions, dry skin, ileus, urinary retention
      2. Tachycardia, hyperthermia
  4. Alpha1 Receptor Blockade
    1. Sedation, orthostatic hypotension, miosis
  5. Inhibition of amine reuptake
    1. Sympathomimetic effects
    2. Myoclonus, hyperreflexia
    3. Serotonin Syndrome (only when used in combination w/ other serotonergic agents)

Diagnosis

  1. Serious toxicity
    1. Conduction delays, SVT, V-tach, hypotension
    2. Respiratory depression
    3. Seizures
    4. Pulmonary Edema
  2. ECG
    1. Sinus Tachycardia (most frequent dysrhythmia)
    2. PR, QRS, QT Prolongation
    3. Right axis deviation (of terminal 40ms)
      1. Terminal R wave in aVR, S wave in I/aVL[1]
    4. Brugada pattern (15%)[2]

TCA Toxicity.jpg

Treatment

GI Decontamination

  1. Gastric lavage if <1hr after ingestion
  2. Activated charcoal 1gm/kg x1

Cardiac Toxicity[3]

Sodium Bicarbonate

  1. Indications:
    1. QRS >100ms, terminal RAD >120 deg, Brugada pattern, ventricular dysrhythmias
  2. Initial Dosing:
  3. Give 1-2 mEq/kg as rapid IVP; may repeat as necessary (stop if pH > 7.55)
  4. May give as 2-3 vials or prefilled syringes (50mL each) of 8.4% NaHCO3
  5. Infusion Dosing
    1. Mix 125-150 mEq of NaHCO3 in 1L of D5W; infuse at 250 mL/hr
  6. Treatment Goal:
  7. QRS <100ms
  8. pH 7.50-7.55
  9. Treatment Monitoring
    1. Monitor for volume overload, hypokalemia, hypernatremia, metabolic alkalosis

Hyperventilation

  • Consider in patients unable to tolerate NaHCO3 (renal failure, pulm/cerebral edema)

Lidocaine

  • Consider for ventricular dysrhythmias if NaHCO3 alone is ineffective
NOTE
avoid IA, IB, IC antiarrhythmics, Beta-Blockers, and Calcium Channel Blockers

Phenytoin

  • Consider for ventricular dysrhythmias resistant to NaHCO3 and lidocaine

Synchronized cardioversion

  • Appropriate in pts w/ persistent unstable tachydysrhythmias

Seizures

  1. Benzodiazapines are 1st line
  2. Barbituates or Propofol are 2nd line

Hypotension

  • After repeat fluid boluses and with sodium load from NaHCO3 norepinepherine should be the first line vasopressor
  • ECMO is a successful adjunct for refractory hypotension after maximal therapy has failed

Dialysis

Not useful for enhancing elimination due to the large volume of distribution and high lipid solubility

Disposition

  • Consider discharge for pts who remain asymptomatic after 6hr of observation

See Also

Source

  • Tintinalli
  • UpToDate
  1. ↑ Liebelt EL, Francis PD, Woolf AD. ECG lead aVR versus QRS interval in predicting seizures and arrhythmias in acute tricyclic antidepressant toxicity. Ann Emerg Med. Aug 1995;26(2):195-201
  2. ↑ Monteban-Kooistra WE, van den Berg MP, Tulleken JE. Brugada electrocardiographic pattern elicited by cyclic antidepressants overdose. Intensive Care Med. Feb 2006;32(2):281-5
  3. ↑ Thanacoody HK, Thomas SH. Tricyclic antidepressant poisoning: cardiovascular toxicity. Toxicol Rev. 2005;24(3):205-14
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