A 55-year-old man on phenelzine 45 mg/day for atypical depression eats a large portion of aged cheese and develops a severe headache, diaphoresis, palpitations, and a blood pressure of 210/120 mmHg. Which mechanism underlies this hypertensive crisis?
- A Excessive serotonin accumulation in the central nervous system
- B Acetylcholine excess at autonomic ganglia due to MAO-B inhibition
- C Unopposed alpha-adrenergic stimulation from peripheral tyramine-induced norepinephrine release ✓
- D Histamine release from mast cells triggered by dietary amines
Correct answer: C. Unopposed alpha-adrenergic stimulation from peripheral tyramine-induced norepinephrine release
Explanation
MAOIs inhibit gut and hepatic MAO-A, which normally metabolises dietary tyramine. Ingested tyramine enters the circulation and displaces norepinephrine from sympathetic nerve terminals, causing massive alpha-adrenergic stimulation and hypertensive crisis. Option A describes serotonin syndrome. Option B is incorrect as phenelzine inhibits MAO-A, not selectively MAO-C. Option D describes anaphylaxis, not tyramine reaction.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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