NAPLEX Question of the Week: Beta Blocker Bonanza

How versed are you in beta blockers? Find out this week with our challenge question!
NAPLEX Question of the Week: Beta Blocker Bonanza

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A 57-year-old male patient was admitted to the hospital after exhibiting altered mental status, hypotension (BP 80/40 mmHg), and bradycardia (45 BPM). He has a history of gout, hypertension, depression, and previous myocardial infarction. The patient is reported to be taking allopurinol 100mg once daily, Prinivil 40mg once daily, sertraline 100mg once daily, chlorthalidone 25mg once daily in the morning, and metoprolol (dose and frequency unknown). It is determined that our patient is most likely suffering from beta blocker toxicity. 
Which of the following statements are true when it comes to beta blockers? 
A. Beta blocker toxicity may be treated with adenosine 
B. Beta blockers are a first line treatment agent for uncomplicated hypertension as well as heart failure with reduced ejection fraction (HFrEF)
C. Beta blockers can mask several symptoms of hypoglycemia
D. Patients who are poor CYP 2D6 metabolizers may be at increased risk of metoprolol accumulation leading to toxicity
E. Atenolol, bisoprolol, nebivolol and propranolol are (β2) cardioselective 
Answers with rationale:
Answers C and D are correct.
Answer A is incorrect because adenosine (Adenocard/Adenoscan) is a Class IV antiarrhythmic used for paroxysmal supraventricular tachycardia (PSVT) and would lower the patient's heart rate even further. What instead would potentially be used is atropine (AtroPen), an anticholinergic agent that increases cardiac output and treats bradycardia. It is important to also note that during beta blocker toxicity, many other drugs are also used as part of treatment such as fluids to manage hypotension and even sometimes glucagon (Gvoke) which is considered an antidote for beta blocker toxicity. Answer B is incorrect because beta blockers are not first line treatment for uncomplicated hypertension due to worse outcomes compared to other first-line agents (increased risk of stroke). Beta blockers are considered a part of first-line treatment for patients with ischemic heart disease, such as our patient who has had a previous myocardial infarction, and in patients with heart failure with reduced ejection fraction (HFrEF). If used for HFrEF, the only three beta blockers recommended are metoprolol succinate (Toprol XL), bisoprolol (Ziac) and carvediol (Coreg). Answer C is correct because beta blockers can mask tachycardia during a hypoglycemic episode. It is important to counsel patients with diabetes who take beta blockers that these symptoms of hypoglycemia may be masked, but sweating is not masked by beta blockers. Metoprolol succinate (Toprol XL) and metoprolol tartrate (Lopressor) are both metabolized via CYP 2D6, making answer D correct as poor metabolizers may allow accumulation leading to toxicity. Answer E is incorrect because cardioselective beta blockers target Beta-1 receptors found in cardiac muscle whereas Beta-2 receptors are primarily located in the lungs. In addition, propranolol (Inderal) is not cardioselective and blocks both beta-1 and beta-2 receptors. 
NAPLEX Competency Statements covered:
2.1 – Pharmacology, mechanism of action, or therapeutic class
3.4 – Drug dosing or dosing adjustments; duration of therapy
3.6 – Drug contraindications, allergies, or precautions
3.7 – Adverse drug effects, toxicology, or overdose
3.11 – Evidence-based practice
Hope everyone had a great Thanksgiving!
Dr. B

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