In patients undergoing surgery while on phenelzine (Nardil), which medication should be avoided to prevent hypertensive crisis?

Phenelzine is a non-selective monoamine oxidase inhibitor (MAOI) that can lead to hypertensive crises when certain medications are administered. Indirect acting vasopressors are particularly concerning because they can increase norepinephrine levels without direct stimulation of adrenergic receptors, potentially causing a significant rise in blood pressure in patients who are on MAOIs like phenelzine.

This happens because MAOIs inhibit the breakdown of amines, including tyramine, which are found in many indirect vasopressors. If a patient on phenelzine receives an indirect vasopressor, the resulting accumulation of catecholamines can precipitate a hypertensive crisis, which is a medical emergency characterized by excessively high blood pressure that can lead to serious complications.

Inducing agents, pain medications, and antibiotics do not typically interact in the same way with MAOIs to cause hypertensive crises. While caution is always warranted when administering any drugs to patients on MAOIs, particularly with certain sedatives and analgesics, indirect acting vasopressors pose the highest risk for the aforementioned complications. Therefore, avoiding indirect acting vasopressors is crucial in the surgical setting for patients taking phenelzine.