In acute tricyclic antidepressant overdose, which intervention addresses sodium channel blockade and is commonly used as part of management?

• A. Atropine
• B. Sodium bicarbonate
• C. Calcium gluconate
• D. Diphenhydramine

Answer: (B)

In acute tricyclic antidepressant overdose the dangerous effect on the heart comes from blockade of the fast sodium channels, which slows conduction and widens the QRS. The intervention that best counters this specific problem is intravenous sodium bicarbonate. It works by two complementary actions: raising the extracellular sodium concentration to overcome the channel blockade, and alkalinizing the serum to around the therapeutic range (pH ~7.45–7.55), which reduces the drug’s affinity for sodium channels and improves myocardial conduction. Clinically, you monitor for a widened QRS or hemodynamic instability and treat with bicarbonate accordingly, often starting with a bolus and continuing infusion to achieve the target pH and safety.

Other options don’t address the sodium channel blockade: atropine targets cholinergic effects, not the cardiac sodium channels; calcium gluconate is used for calcium channel blocker overdose or certain electrolyte disturbances; diphenhydramine is an antihistamine with anticholinergic effects and can worsen conduction issues.