Fenelzin

Fenelzin, also spelled phenelzine, is a non-selective, irreversible monoamine oxidase inhibitor (MAOI) used as an antidepressant. It inhibits MAO-A and MAO-B, increasing brain levels of serotonin, norepinephrine, and dopamine.

Fenelzin is typically used for major depressive disorder that has not responded to other treatments or presents with atypical features. It has also been employed in certain anxiety disorders, though safety concerns limit its use as a first-line option.

Mechanism and pharmacokinetics: By irreversibly blocking MAO, fenelzin reduces the breakdown of monoamines, enhancing monoaminergic neurotransmission. It is administered by mouth and metabolized in the liver. The inhibition persists after the drug is cleared, which means effects can last beyond discontinuation and requires a washout period when switching to or from other antidepressants to minimize interactions.

Dosing and monitoring: Dosing is typically started at about 15 mg three times daily and titrated to a usual maximum around 60 mg per day, with careful clinical supervision. Patients must follow dietary restrictions to limit tyramine intake and reduce the risk of hypertensive crisis. Blood pressure and psychiatric symptoms are monitored regularly.

Safety and interactions: Fenelzin can cause hypertensive crisis if combined with tyramine-rich foods or certain medications, including SSRIs, SNRIs, TCAs, meperidine, tramadol, linezolid, and decongestants. Other serotonergic agents require appropriate washout periods when switching to or from MAOIs.

History and status: Fenelzin is one of the older MAOIs and has largely been supplanted by newer antidepressants due to safety concerns, including dietary restrictions and drug interactions. It remains in use in some settings where other treatments have failed.