Tricyclic antidepressant (TCA) poisoning
TCA overdose is a frequent and potentially life‑threatening presentation. Amitriptyline and dosulepin (dothiepin) are among the most toxic in overdose and require early recognition and directed treatment.
This summary is emergency department (ED) focused and aligned with contemporary UK guidance (RCEM, RCEM/NPIS, Resuscitation Council, NICE). For agent‑specific or unusual scenarios, contact your local poisons service / TOXBASE / NPIS early.
Pathophysiology - why TCAs are dangerous
- Therapeutic effect: inhibition of presynaptic norepinephrine and serotonin reuptake.
- In overdose, TCAs block multiple receptors and ion channels:
- Muscarinic (anticholinergic): dry mouth, mydriasis, hyperthermia, agitation, ileus, urinary retention.
- Alpha‑adrenergic: vasodilation leading to hypotension.
- Histaminic: sedation.
- Voltage‑gated cardiac channels: fast sodium‑channel blockade causing slowed phase‑0 depolarisation and QRS widening; potassium‑channel blockade causing QT prolongation. There is also a direct negative inotropic effect.
- The combination of sodium‑channel blockade (conduction delay) and anticholinergic effects (tachycardia) predisposes to seizures, conduction block and ventricular arrhythmias.
Clinical features
- Time course: usually within hours; may be delayed with sustained‑release preparations.
- Common (anticholinergic) features: agitation, confusion, dry mucous membranes, flushed skin, mydriasis, blurred vision, reduced bowel sounds, urinary retention, sinus tachycardia, fever.