Amitriptyline poisoning with QRS prolongation — MRCEM SBA MCQ

Instant feedback + full explanation. One question, done properly.

EasyToxicology and environmental emergenciesAmitriptyline poisoning with QRS prolongationMRCEM SBA

A 34-year-old woman attends the emergency department approximately two hours after taking an unknown number of her prescribed amitriptyline tablets. She is alert but restless, with dry skin and dilated pupils. Her heart rate is 126 beats/min and blood pressure is 116/74 mmHg. The ECG shows sinus tachycardia with a QRS duration of 148 ms. Venous pH is 7.39 and potassium is 4.1 mmol/L. She is on continuous cardiac monitoring. Which intravenous treatment should be given next?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Administer sodium bicarbonate

The ingestion and anticholinergic findings support amitriptyline poisoning. More importantly, the markedly widened QRS indicates clinically significant cardiac conduction toxicity despite a preserved blood pressure. UK emergency medicine guidance supports intravenous sodium bicarbonate for QRS prolongation associated with tricyclic antidepressant overdose, even when the initial blood pH is normal. Treatment should be followed by repeat ECG and blood-gas assessment while cardiac monitoring continues. ([heeoe.hee.nhs.uk](https://heeoe.hee.nhs.uk/sites/default/files/tricyclic_antidepressant_od_cem5075-gemnet-2009_0.pdf?utm_source=openai)) Magnesium sulphate is a plausible response to a dangerous arrhythmia, but the rhythm shown is sinus tachycardia with QRS widening, not an arrhythmia for which magnesium takes priority. Diazepam would be appropriate for a seizure or agitation requiring sedation; she is restless but alert, and neither problem supersedes the ECG abnormality. Intravenous saline could help initial resuscitation if she were hypotensive or hypovolaemic, but it does not treat this conduction disturbance. Calcium gluconate would be relevant to cardiac toxicity from hyperkalaemia; her potassium is normal and the history points instead to tricyclic antidepressant toxicity. ([heeoe.hee.nhs.uk](https://heeoe.hee.nhs.uk/sites/default/files/tricyclic_antidepressant_od_flowchart_cem5075-gemnet-2009_0.pdf?utm_source=openai))

Reference: GEMNet: Guideline for the Management of Tricyclic Antidepressant Overdose (December 2009) — https://heeoe.hee.nhs.uk/sites/default/files/tricyclic_antidepressant_od_cem5075-gemnet-2009_0.pdf GEMNet: Evidence-based Flowchart for the Management of Tricyclic Antidepressant Overdose (December 2009) — https://heeoe.hee.nhs.uk/sites/default/files/tricyclic_antidepressant_od_flowchart_cem5075-gemnet-2009_0.pdf