An intentional overdose of propranolol produces severe bradycardia of 38 bpm and profound hypotension refractory to fluids and atropine. What is the specific first-line antidote?

Answer and explanation

Correct answer: B. Intravenous glucagon

  1. Step 1: Severe beta-blocker toxicity causes refractory myocardial depression by blocking beta-adrenergic G-protein-coupled adenylyl cyclase activation.
  2. Step 2: Glucagon binds to independent glucagon receptors on cardiomyocytes, stimulating adenylyl cyclase directly and increasing intracellular cAMP to restore heart rate and contractility.
Answer
Intravenous glucagon.
Why not the others: Sodium bicarbonate is the antidote for tricyclic antidepressant cardiotoxicity to overcome sodium channel blockade. Dimercaprol is a heavy metal chelator used for arsenic, gold, and lead poisoning. Activated charcoal adsorbs ingested substances if given early but cannot reverse established cardiogenic shock.

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