Tricyclic antidepressants

TCA overdose accounts for 50% of ICU poisoning admissions

Toxicity

  1. Cholinergic antagonism
  2. Sodium channel blockade

Features

Cardiovascular

  • Tachycardia
  • Arrhythmia (risk increased when QRS duration >100ms
  • Hypotension

Neurological

  • Dilated pupils
  • Blurred vision
  • Reduced conscious level
  • Seizures (risk increased when QRS duration >160ms)

Respiratory

  • Respiratory depression
  • Gastrointestinal
  • Dry mouth
  • Reduced gastric emptying

Other

  • Urinary retention

All patients require continuous / serial ECG monitoring

Management

Consider activated charcoal (extended therapeutic window due to reduced gastric emptying

Manipulate pH

  • Give sodium bicarbonate if ECG changes
  • Consider hyperventilation if mechanically ventilated
  • May reduce the available ionised free drug
  • Sodium bicarbonate provides high sodium load which may overcome sodium channel blockade

Consider benzodiazepines in seizures rather than phenytoin due to its sodium channel-blocking effects