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.
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 |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Beta blocker, WBRKeyword::Beta-blocker, WBRKeyword::Overdose, WBRKeyword::Toxicity, WBRKeyword::Antidote, WBRKeyword::Glucagon, WBRKeyword::Heart block |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |