WBR0938

Author	PageAuthor::William J Gibson
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::Correct: Glucagon counteracts beta-blocker toxicity by increasing intracellular cAMP.
Answer B	AnswerB::Epinephrine
Answer B Explanation	AnswerBExp::Incorrect: Epinephrine can be administered in the case of anaphylaxis.
Answer C	AnswerC::Digoxin
Answer C Explanation	AnswerCExp::Incorrect: While digoxin has an inotropic effect, it is not appropriate for counteracting beta-blocker overdose.
Answer D	AnswerD::Verapamil
Answer D Explanation	AnswerDExp::Incorrect: 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::Incorrect: 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::Beta-blockers such as propranolol interfere with the binding of catecholamine stress hormones such as epinephrine to beta-adrenergic receptors*. 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. 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. Educational Objective: Glucagon counteracts beta-blocker toxicity by increasing intracellular cAMP. References: First Aid 2013 page 239 ; First Aid 2012 page 270 Weinstein RS, Cole S, Knaster HB, Dahlbert T (February 1985). "Beta blocker overdose with propranolol and with atenolol". Ann Emerg Med14 (2): 161–163 Educational Objective: References: ]]
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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