Monoamine oxidase inhibition by phenelzine and brofaromine in healthy volunteers

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Abstract
The two monoamine oxidase (MAO) inhibitors phenelzine and brofaromine given for 2 to 3 weeks were compared in six volunteers. Blood pressure sensitivity to intravenous tyramine increased 2.6‐fold during phenelzine (60 mg/day) and 4.8‐fold during brofaromine, whereas sensitivity to oral tyramine increased more during phenelzine (15.7‐fold vs 8.5‐fold). After withdrawal of phenelzine, pressor sensitivity to oral tyramine returned to control values within 2 and for more than 8 weeks. Relative bioavailability of conjugated tyramine was elevated sixfold by brofaromine and 11.6‐fold by phenelzine. Urinary elimination of tryptamine increased during phenelzine and brofaromine to 12.7‐fold and threefold, respectively. 3‐Methoxy‐4‐hydroxyphenylglycol (MHPG) and 3‐methoxy‐4‐hydroxymandelic acid (VMA) excretion decreased during brofaromine significantly by 72% and 49%, respectively. The nonsignificant decrease of MHPG excretion and the increase of intravenous tyramine pressor sensitivity caused by phenelzine are significantly related. The data suggest that the selective reversible MAO‐A inhibitor brofaromine has a larger therapeutic safety than phenelzine. Clinical Pharmacology and Therapeutics (1989) 45, 260–269; doi:10.1038/clpt.1989.26