The correct answer is C. Patients with nonallergic bronchospastic conditions, such as emphysema and chronic bronchitis, are generally not prescribed non-selective beta-blockers due to bronchoconstriction. Beta-2 receptors in the respiratory tract act via the Gs pathway, and stimulation results in cAMP release and smooth muscle relaxation. Thus, beta-2 blockade can produce smooth muscle contraction, which, in the airway, results in bronchoconstriction.
However, lower doses of selective beta-1 receptor antagonists ("cardioselective"), such as metoprolol and atenolol, are relatively well tolerated in patients with emphysema due to relatively low levels of beta 2 antagonism. As a precautionary measure, emphysema patients receiving beta-1-selective blocking agents should also use a bronchodilator with beta-2-stimulating activity. It is also important to note that as the dose of the beta-1-selective agent increases, the "beta-1 receptor selectivity" also begins to decrease. Hence, patients with bronchospastic disorders are unlikely to tolerate moderate-high doses of beta-1-selective antagonists
Beta-blockers should also be used cautiously in diabetic patients on insulin products because they can mask the premonitory symptoms of hypoglycemia (e.g., tachycardia).
Most beta-blockers whose names start with A-M are beta-1-selective. A mnemonic to remember some of the more common beta-1 blockers is A BEAM (acebutolol, betaxolol, esmolol, atenolol, and metoprolol).
Furosemide (choice A) and hydrochlorothiazide (choice B) are loop and thiazide diuretics, respectively. Both of these agents are contraindicated for use in a patient with a past history of hypersensitivity to sulfonamides. Our patient had a prior anaphylactic reaction to trimethoprim/sulfamethoxazole, a sulfonamide antibiotic.
Propranolol (choice D) and sotalol (choice E) are nonselective beta receptor antagonists and should not be used in the treatment of hypertension in patients with bronchospastic disease. They can exacerbate bronchoconstriction due to their greater beta-2 blockade activity, and thus are likely to exacerbate pulmonary symptoms.
This is a multi-step question.
What is the question asking?
This question asks you to choose the most appropriate medication based on a patient?s current medical condition while taking into consideration his past medical and allergy history.
What is the first step?
The first step is to determine what types of medication would be contraindicated for use in this patient based on his past medical and allergy history. In this case, the following considerations should be made:
- With a past medical history of emphysema, non-selective beta-adrenergic receptor antagonists would not be recommended.
- With a past allergy history involving the sulfonamide trimethoprim/sulfamethoxazole, medications containing a sulfa component would be contraindicated.
What is the next step?
The next step is to choose a medication for hypertension that does not contain non-selective beta-adrenergic receptor antagonist properties or classified as a sulfonamide. In this case, the treatment of choice is the beta-1 selective blocking agent metoprolol.
Can other answers be eliminated?
Once we have determined that the non-selective beta-adrenergic receptor antagonists and sulfonamides are contraindicated, the following can be eliminated:
- Furosemide (choice A), a loop diuretic, and hydrochlorothiazide (choice B), a thiazide diuretic, are classified as sulfonamides.
- Propranolol (choice D) and sotalol (choice E) are nonselective beta receptor antagonists.
What is the single best answer and why?
The best answer is metoprolol (choice C) because it is a beta-1 selective blocker used to treat hypertension. Since it is not classified as a sulfonamide, it can be used safely in a patient with a past history of anaphylaxis to a sulfa drug.
MedEssentials (4th Ed.): pp. 193, 269, 525
First Aid (2019): pp. 245.1, 318.1
First Aid (2018): pp. 241.1, 316.1
First Aid (2017): pp. 237.1, 309.1
Pathoma (2018-2019): pp. 121.1
Pathoma (2014-2017): pp. 121.1
