A 22-year-old woman is brought unconscious after ingesting an unknown quantity of her mother's amitriptyline tablets. She is hypotensive and seizing. ECG shows sinus tachycardia with a QRS duration of 168 ms. The single most appropriate next drug is:

• A Intravenous amiodarone
• B Intravenous physostigmine
• C Oral activated charcoal followed by gastric lavage
• D Intravenous sodium bicarbonate bolus ✓

Explanation

Tricyclic antidepressant toxicity produces cardiac conduction delay through sodium channel blockade, seen as a widened QRS, along with hypotension, seizures and arrhythmias. Intravenous sodium bicarbonate alkalinises the blood and raises extracellular sodium, which overcomes the channel blockade and narrows the QRS; it is the specific antidotal therapy when the QRS exceeds 100 to 120 ms. Amiodarone is avoided in sodium channel blocker toxicity. Physostigmine can provoke seizures and bradyarrhythmias in TCA poisoning and is not recommended.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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Written and medically reviewed by the StethoPrep medical team.