Overdose of tricyclic antidepressants is a common presentation to emergency departments. Amitriptyline and dosulepin (dothiepin) are particularly dangerous in overdose.

Early features relate to anticholinergic properties: dry mouth, dilated pupils, agitation, sinus tachycardia, blurred vision.

Features of severe poisoning include:

• arrhythmias
• seizures
• metabolic acidosis
• coma

ECG changes include:

• sinus tachycardia
• widening of QRS
• prolongation of QT interval

Widening of QRS > 100ms is associated with an increased risk of seizures whilst QRS > 160ms is associated with ventricular arrhythmias

Management

• IV bicarbonate
  • first-line therapy for hypotension or arrhythmias
  • indications include widening of the QRS interval >100 msec or a ventricular arrhythmia
• other drugs for arrhythmias

• class 1a (e.g. Quinidine) and class Ic antiarrhythmics (e.g. Flecainide) are contraindicated as they prolong depolarisation

• class III drugs such as amiodarone should also be avoided as they prolong the QT interval
• response to lignocaine is variable and it should be emphasized that correction of acidosis is the first line in management of tricyclic induced arrhythmias
• intravenous lipid emulsion is increasingly used to bind free drug and reduce toxicity
• dialysis is ineffective in removing tricyclics