Tyramine and MAO inhibitors: Mechanism

Patients on Monoamine oxidase inhibitors (MAO) inhibitors (especially MAO-A inhibitors or non-selective MAO inhibitors) are advised to avoid Tyramine rich foods.

• Tyramine rich foods: sauerkraut, chicken liver, chocolate, and cheeses (Cheddar, Gruyère, and Stilton are especially high), alcohol/ wine, pickled fish (herring), broad beans, yeast extracts, tofu and soy sauce.

MECHANISM: Tyramine is a byproduct of Tyrosine metabolism by MAO in the liver. Typically it will have low bioavailability due to extensive first-pass effect in the liver. 

If the patient is taking a MOA inhibitor, Tyramine accumulates in the bloodstream; it has indirect sympathomimetic action causing the release of stored catecholamines. This is known as the “Cheese effect”!!!

Onset is typically rapid (15 mins- 1hr); the hallmark presentation of the Tyramine “Cheese” reaction are HYPERTENSION + SEVERE HEADACHE (occipital or temporal), palpitations, nausea and vomiting. Typically resolving within 4-6 hours, however can be fatal!

NOTE: Selegiline (MAO-B selective) and rasagiline do not functionally inhibit MAO-A and are not associated with the “Cheese effect” with doses typically used in clinical practice!

REFERENCES

1.  CHAPTER 9: Adrenoceptor Agonists & Sympathomimetic Drugs. Basic & Clinical Pharmacology, 13e. Italo Biaggioni; David Robertson
2.  Chapter 179: Monoamine Oxidase Inhibitors. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e. Frank LoVecchio