A 50-year-old woman on phenelzine (MAOI) for treatment-resistant depression inadvertently eats a tyramine-rich meal (aged cheese, red wine). She develops a hypertensive crisis (BP 220/130 mmHg), severe headache, and diaphoresis. The mechanism of this interaction is:
- A Tyramine directly activates postsynaptic alpha-1 receptors in peripheral vasculature
- B MAOI inhibits dopamine-beta-hydroxylase, causing dopamine to convert to tyramine in sympathetic neurons
- C Tyramine, normally inactivated by MAO-A in the gut/liver, accumulates and enters sympathetic terminals where it displaces norepinephrine, causing massive sympathomimetic release ✓
- D Phenelzine competes with phenylalanine for amino acid transport, causing norepinephrine overflow
Correct answer: C. Tyramine, normally inactivated by MAO-A in the gut/liver, accumulates and enters sympathetic terminals where it displaces norepinephrine, causing massive sympathomimetic release
Explanation
The tyramine 'cheese reaction' with MAOIs: tyramine is normally inactivated by intestinal and hepatic MAO-A before systemic absorption. When MAO is inhibited, dietary tyramine is absorbed intact and enters sympathetic nerve terminals, where it displaces stored norepinephrine (an indirect sympathomimetic) causing massive NE release, resulting in a hypertensive crisis. Management: phentolamine (alpha-blocker) IV or nifedipine. Serotonin syndrome (different from cheese reaction) occurs when MAOIs combine with serotonergic drugs.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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