Phenelzine is a derivative of hydrazine, which is phenylethylamine-like moiety and similar to normal substrates of MAO. When MAO tries to oxidize phenelzine, this hydrazine-moiety binds covalently to the enzyme, thus inactivating it irreversibly. Phenelzine is a non-selective MAO-inhibitor, it inhibits both MAO-A and MAO-B. Furthermore, primarily through its primary metabolite, PEH (phenylethylidenehydrazine), phenelzine elevates levels of GABA in the caudate-putamen and nucleus accumbens. This may contribute to its anxiolytic properties and superior efficiacy in treating severe anxiety.

Pharmacokinetics

Phenelzine is administered orally as phenelzine sulphate and it is rapidly absorbed form the gastro-intestinal tract. Although phenelzine has a fairly short half-life, its effect lasts for several weeks, until new functional MAO-enzymes have been produced by the body. Phenelzine is acetylated in the liver and its metabolites are excreted in the urine.

Side effects

Common side effects include orthostatic hypotension, dizziness, headache, fatigue and gastro-intestinal disturbances. Phenelzine can cause, though rarely, severe hepatotoxicity, most likely due to its hydrazine group.

As with other MAOIs, tyramine-containing foods can cause a cheese reaction, which is a severe hypertensive crisis, so users of phenelzine must adhere to rigid dietary guidelines. This hypertensive crisis is characterised by severe headache and rapid rise in blood pressure, which can cause cardiac failure and intracranial hemorrhage.

Nardil formulation

Recently, the formula for Nardil was changed due to one of the constituents being discontinued by its manufacturer. Many users experienced difficulties following this change, as the new formulation sometimes required a higher dosage to achieve the same result. Currently, there are some 10.000 to 15.000 people taking Nardil worldwide.