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

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
   2. Peripheral
      1. Mydriasis, decreased secretions, dry skin, ileus, urinary retention
      2. Tachycardia, hyperthermia
4. Alpha 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
   4. Brugada pattern (15%)

Treatment

1. GI Decontamination
   1. Gastric lavage if <1hr after ingestion
   2. Activated charcoal 1gm/kg x1
2. Cardiac Toxicity
   1. Sodium Bicarbonate
      1. Indications:
         1. QRS >100ms, terminal RAD >120deg, Brugada pattern, ventricular dysrhythmias
      2. Dosing
         1. Give 1-2 mEq/kg as rapid IVP; may repeat as necessary (stop if pH > 7.55)
            1. May give as 2-3 vials or prefilled syringes (50mL each) of 8.4% NaHCO3
         2. If effective, start infusion
            1. Mix 125-150 mEq of NaHCO3 in 1L of D5W; infuse at 250 mL/hr
      3. Goal
         1. QRS <100ms
         2. pH 7.50-7.55
      4. Monitoring
         1. Monitor for volume overload, hypokalemia, hypernatremia, metabolic alkalosis
   2. Hyperventilation
      1. Consider in pts unable to tolerate NaHCO3 (renal failure, pulm/cerebral edema)
   3. Lidocaine
      1. Consider for ventricular dysrhythmias if NaHCO3 alone is ineffective
   4. Phenytoin
      1. Consider for ventricular dysrhythmias resistant to NaHCO3 and lidocaine
   5. Synchronized cardioversion
      1. Appropriate in pts w/ persistent unstable tachydysrhythmias
   6. Avoid IA, IB, IC, BBs, and CCBs
3. Seizures
   1. Benzodiazapines are 1st line
   2. Barbitutate are 2nd line
   3. Phenytoin is ineffective
4. Hypotension
   1. IVF 10mL/kg; pulmonary edema can develop if excessive fluids given
   2. Give NaHCO3 if fluids ineffective (regardless of QRS duration)
   3. Give norepi if fluids/NaHCO3 ineffective
      1. Start 1mcg/min; tirate up to 30mcg/min
5. Dialysis not useful

Disposition

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

See Also

• Toxidromes

Source

• Tintinalli
• UpToDate