A patient taking phenelzine (an MAOI) inadvertently consumes aged cheese. He develops severe hypertensive crisis. The interaction is mediated by accumulation of which amine in food?

• A Tyramine ✓
• B Histamine
• C Tryptamine
• D Dopamine

Explanation

The 'cheese effect' is a potentially fatal drug-food interaction in patients taking non-selective MAOIs (e.g., phenelzine, tranylcypromine). Tyramine, a dietary amine abundant in aged cheeses, fermented foods, red wine, and cured meats, is normally inactivated in the gut wall and liver by MAO-A. When MAO-A is inhibited, absorbed tyramine enters systemic circulation, enters sympathetic nerve terminals via the norepinephrine transporter, and displaces norepinephrine from vesicles, causing massive catecholamine release, severe hypertension, headache, and risk of intracranial haemorrhage. MAO-B selective agents (selegiline at low doses) carry lower tyramine interaction risk.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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