A 19-year-old woman is brought unconscious after ingesting an unknown quantity of her amitriptyline. ECG shows sinus tachycardia, QRS duration of 140 ms, and right axis deviation. After securing the airway, the most appropriate immediate drug therapy is:

• A Intravenous amiodarone for the wide-complex arrhythmia
• B Oral activated charcoal followed by intravenous physostigmine
• C Intravenous calcium gluconate followed by insulin-dextrose
• D Intravenous sodium bicarbonate bolus ✓

Explanation

Tricyclic antidepressant cardiotoxicity arises from cardiac sodium channel blockade; sodium bicarbonate alkalinises the blood and provides sodium load, displacing the drug from channels and narrowing the QRS. It is first-line when QRS exceeds 100 ms. Amiodarone and class I agents can worsen toxicity. Physostigmine may provoke seizures and bradyarrhythmias and is avoided. Calcium and insulin-dextrose treat hyperkalaemia, which is absent here.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.