Pharmacology · patient case question
What is the mechanism of action of the medication used to control her hypertension?
Patient case: Cardiac and endocrine medication review
Patient: Female, 62 years old
Chief complaint: “I'm here for a cleaning and a check-up.”
History: Hypertension, gout, arthritis, hypothyroidism, gastro-oesophageal reflux disease. Medications: metoprolol, levothyroxine, allopurinol, calcium carbonate, famotidine.
Findings: Moderately restored dentition, no caries. Blood pressure 142/92 mmHg.
Show answer and explanation
Correct answer: B. Competitive inhibition of β1 receptors
- A. Increased nitric oxide release describes nitrates such as nitroglycerin, used for angina rather than routine hypertension, and hydralazine.
- B. CORRECT. Metoprolol is a CARDIOSELECTIVE beta-blocker. It competitively antagonises β1 receptors, which are concentrated in the heart and in the juxtaglomerular apparatus. The result is reduced heart rate and contractility, so cardiac output falls, and reduced renin release, so the renin-angiotensin-aldosterone system is dampened. Both lower blood pressure.
- C. β2 receptors sit in bronchial and vascular smooth muscle. BLOCKING them causes bronchoconstriction — which is precisely why non-selective agents such as propranolol are avoided in asthma, and why cardioselective metoprolol is preferred.
- D. Calcium channel blockade describes amlodipine, nifedipine, diltiazem and verapamil. The dihydropyridines are the ones associated with gingival enlargement.
Note: Dental relevance: with NON-selective beta-blockers, epinephrine can produce unopposed α stimulation with a hypertensive surge and reflex bradycardia. Limit the vasoconstrictor dose and aspirate carefully. NSAIDs also blunt the antihypertensive effect of beta-blockers over time.