WBR0938

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Author PageAuthor::William J Gibson (Reviewed by Serge Korjian)
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pharmacology
Sub Category SubCategory::Cardiology
Prompt Prompt::A 60-year-old man attempts suicide by consuming his entire bottle of propranolol pills. He suffers extreme cardiovascular collapse and tonic-clonic seizures. Which of the following may serve as an antidote to his overdose?
Answer A AnswerA::Glucagon
Answer A Explanation AnswerAExp::Glucagon counteracts beta-blocker toxicity by increasing intracellular cAMP.
Answer B AnswerB::Epinephrine
Answer B Explanation AnswerBExp::Epinephrine can be administered in the case of anaphylaxis.
Answer C AnswerC::Digoxin
Answer C Explanation AnswerCExp::While digoxin has an inotropic effect, it is not appropriate for counteracting beta-blocker overdose.
Answer D AnswerD::Verapamil
Answer D Explanation AnswerDExp::Verapamil is a calcium channel blocker that can be used to treat cardiac arrhythmias. It is not an effective antidote for beta-blocker overdose.
Answer E AnswerE::Sotalol
Answer E Explanation AnswerEExp::Sotalol is both a non-selective beta-blocker and potassium channel blocker (Class III antiarrhythmic). It is not an effective antidote for beta-blocker overdose.
Right Answer RightAnswer::A
Explanation [[Explanation::Non-selective beta-blockers such as propranolol interfere with the binding of catecholamine stress hormones such as epinephrine to beta-adrenergic receptors at most sites (β1-adrenergic receptors are located mainly in the heart and in the kidneys; β2-adrenergic receptors are located mainly in the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, and skeletal muscle; β3-adrenergic receptors are located in fat cells). Because beta blockers decrease activity in the SA-node, they can lead to bradycardia and first degree heart block. In addition to arrhythmias, beta-blocker overdose may cause CNS depression and seizures. At the molecular level, beta-blockade causes a decrease in intracellular levels of cAMP. Glucagon binds to its G protein-coupled receptor, which then activates adenylate cyclase to increase intracellular levels of cAMP. This cascade counteracts the effects of beta-blocker overdose.

Educational Objective: Glucagon counteracts beta-blocker toxicity by increasing intracellular cAMP.
References: Weinstein RS, Cole S, Knaster HB, Dahlbert T (February 1985). "Beta blocker overdose with propranolol and with atenolol". Ann Emerg Med14 (2): 161–163]]

Approved Approved::Yes
Keyword WBRKeyword::Beta blocker, WBRKeyword::Beta-blocker, WBRKeyword::Overdose, WBRKeyword::Toxicity, WBRKeyword::Antidote, WBRKeyword::Glucagon, WBRKeyword::Heart block
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