Pharmacology · patient case question
What is the mechanism of action of terazosin?
Patient case: Five medication lists in one session
Patient: Four separate patients
Chief Complaint: A: denture soreness. B: needs an antibiotic before an extraction. C: routine review. D: brought in obtunded by her daughter.
Background: A, 68-year-old male: benign prostatic hyperplasia on terazosin, hyperlipidaemia on simvastatin. Denture stomatitis diagnosed today and systemic fluconazole considered. B, 90-year-old female: frail, on no regular medication. C, 71-year-old female: rheumatoid arthritis on methotrexate, osteoporosis on oral alendronate for six years. D, 79-year-old female: long-standing hypothyroidism, ran out of levothyroxine some weeks ago.
Vital Signs: D: T 94.6°F · HR 48 bpm · RR 8 · BP 96/58 mmHg · drowsy and confused
Findings: A: erythematous denture-bearing palatal mucosa. C: panoramic radiograph taken for pre-operative assessment.
Show answer and explanation
Correct answer: A. Alpha-1 adrenergic receptor antagonist
- A. CORRECT. Terazosin, like prazosin and doxazosin, is an ALPHA-1 ADRENERGIC ANTAGONIST. Blocking alpha-1 receptors relaxes vascular smooth muscle, lowering peripheral resistance, and — the reason this patient takes it — relaxes the smooth muscle of the prostate and bladder neck, relieving obstructive urinary symptoms. The dentally relevant adverse effects follow directly from the vasodilatation: FIRST-DOSE and POSTURAL HYPOTENSION with dizziness and syncope, plus drowsiness, nasal congestion and palpitations. Raise the chair slowly and support the patient on standing.
- B. ACE inhibition describes the drugs ending in ‘-pril’, which block conversion of angiotensin I to angiotensin II and characteristically cause a dry cough.
- C. Beta-1 selective antagonism describes metoprolol and atenolol, which lower heart rate and cardiac output. They have no role in prostatic obstruction.
- D. Calcium channel blockade describes amlodipine, nifedipine, diltiazem and verapamil — and among these the dihydropyridines are the ones associated with gingival enlargement.
Note: ⚠️ The recall also asked which finding is NOT associated with terazosin, and keyed BLEEDING. That is right — alpha-1 blockers have no effect on platelets or the coagulation cascade, so no haemostatic modification is required for surgery. The modification they DO require is postural.