WBR0938
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| Author | William J Gibson (Reviewed by Serge Korjian) |
|---|---|
| Exam Type | USMLE Step 1 |
| Main Category | Pharmacology |
| Sub Category | Cardiology |
| 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 | Glucagon |
| Answer A Explanation | Glucagon counteracts beta-blocker toxicity by increasing intracellular cAMP. |
| Answer B | Epinephrine |
| Answer B Explanation | Epinephrine can be administered in the case of anaphylaxis. |
| Answer C | Digoxin |
| Answer C Explanation | While digoxin has an inotropic effect, it is not appropriate for counteracting beta-blocker overdose. |
| Answer D | Verapamil |
| Answer D Explanation | 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 | Sotalol |
| Answer E Explanation | 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 | A |
| 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. |
| Approved | Yes |
| Keyword | Beta blocker, Beta-blocker, Overdose, Toxicity, Antidote, Glucagon, Heart block |
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