Phenelzine

How it works

It irreversibly inhibits monoamine oxidase, increasing central availability of serotonin, noradrenaline and dopamine; restoration of enzyme activity requires synthesis of new monoamine oxidase.

Prescribing in practice

• Patients must avoid tyramine-rich foods and sympathomimetic or serotonergic drugs because of the risk of severe hypertensive crisis (the 'cheese reaction') and serotonin syndrome.
• Adequate washout periods are required when switching to or from other antidepressants, including a longer interval after stopping fluoxetine.
• Postural hypotension, insomnia and hepatotoxicity may occur, and abrupt withdrawal should be avoided.

Monitoring

Monitor blood pressure, mental state and liver function, and remain alert for signs of hypertensive crisis or serotonin toxicity.

Counselling the patient

• You will be given a list of foods and medicines to avoid, including mature cheese, cured meats and yeast extracts; follow it carefully.
• Tell any healthcare professional or pharmacist that you take a MAOI before starting any new medicine, including over-the-counter remedies.
• Seek urgent help if you develop a severe throbbing headache, palpitations or chest pain.

Evidence & guidelines

The dietary and drug interaction precautions for irreversible MAOIs such as phenelzine are well established and reinforced by MHRA and SPC guidance.