FFinalistSouthampton · 2027
Acute care
AKT · Acute care/Toxicology & overdoselow yield

Tricyclic antidepressant overdose

Sodium-channel blockade + anticholinergic + alpha-blockade

Overview

A dangerous overdose causing the anticholinergic toxidrome plus the two killers: cardiotoxicity (sodium-channel blockade → broad QRS, arrhythmia) and seizures. IV sodium bicarbonate is the key antidote for QRS widening/arrhythmia.

Recognise

  • Anticholinergic: dry, hot, dilated pupils, urinary retention, agitation/delirium, tachycardia
  • Cardiac: broad QRS, tall R in aVR, arrhythmia, hypotension
  • CNS: drowsiness, seizures, coma

Red flags

  • QRS >100–120 ms, ventricular arrhythmia, seizures, hypotension, metabolic acidosis

Differentials & how to tell them apart

Other sodium-channel-blocker overdosesimilar ECG; history
Anticholinergic toxidrome (other)antihistamine/antipsychotic — but TCA adds QRS widening
Sympathomimetic overdosesimilar agitation/tachycardia, no QRS widening

Investigations

ECG (QRS width, aVR R wave) — the prognostic marker; venous gas, glucose, U&E; paracetamol/salicylate co-ingestion screen.

Management

IV sodium bicarbonate for QRS widening/arrhythmia; benzodiazepines for seizures; supportive ICU care

  1. 1ABCDE + continuous ECG. Broad QRS or ventricular arrhythmia or significant acidosis → IV sodium bicarbonate. Seizures → IV benzodiazepine.Gate: AVOID class Ia/Ic and class III antiarrhythmics (they worsen sodium-channel blockade and QT) — use sodium bicarbonate instead
  2. 2Activated charcoal if early/airway protected; supportive ICU care; correct hypotension/acidosis.
IV sodium bicarbonate — for QRS widening / ventricular arrhythmia / significant acidosis
IV benzodiazepine — for seizures
Activated charcoal — if early and airway protected

Key points

QRS width predicts seizures/arrhythmia. Bicarbonate (not standard antiarrhythmics) is the cardiac treatment. The R wave in aVR is a classic clue.

Monitor & prognosis

Continuous ECG (QRS), pH, GCS, seizures.

Good with bicarbonate + supportive care; arrhythmia/seizure if untreated.

Source: TOXBASE; BNF