Principles of using irreversible nonselective monoamine oxidase inhibitors (MAOIs)

Monoamine oxidase inhibitors (MAOIs) can cause significant hypertension when combined with indirectly acting sympathomimetic amines (eg phenylephrine, pseudoephedrine, phentermine, methylphenidate, amfetamines) or certain foods (see Irreversible nonselective monoamine oxidase inhibitor dietary guidelines for dietary guidelines)—avoid concurrent administration. A throbbing headache (usually occipital) is the first symptom; any hypertensive episode should be treated urgently (see Urgent control of elevated blood pressure).

Directly acting sympathomimetic amines (eg adrenaline [epinephrine], dopamine, isoprenaline, noradrenaline [norepinephrine]) are inactivated primarily by catechol-O-methyltransferase, not monoamine oxidase; they can be used cautiously in combination with a MAOI while monitoring blood pressure.

For a detailed listing of drug interactions with MAOIs, see the product information for individual drugs or an appropriate reference (eg Stockley’s Drug Interactions). Always check for drug interactions before prescribing.

Avoid administration of MAOIs with other serotonergic drugs because there is an increased risk of serotonin toxicity (see Drugs most commonly associated with serotonergic toxidrome for drugs that have been associated with serotonin toxicity).