Monoamine Oxidase Inhibitors: An Important but Underutilized Treatment Part I Efficacy

Abstract

HISTORY AND BACKGROUND Monoamine oxidase (MAO) is an enzyme that converts biogenic amines to their corresponding aldehydes. In the brain, its primary substrates are epinephrine (EPI), norepinephrine (NE), dopamine (DA), and serotonin (5-HT). Tyramine is also catabolized by MAO after being absorbed from the gastrointestinal tract or after being generated by bacterial metabolic transformations. Johnston first demonstrated the existence of 2 forms of MAO in the brain, type A (MAO-A) and type B (MAO-B), which differ in their substrate affinities and inhibitor sensitivities. During the late 1940s, isoniazid and related compounds were used to treat tuberculosis but also produced unanticipated mood elevation. Later, it was determined that these drugs shared an ability to inhibit the MAO enzyme and increase the levels of 5-HT, NE, and DA in the brain. Hence, (MAOIs were the first class of antidepressant drugs to be identified and have long been recognized as efficacious for the treatment of depression. However, because of reports of acute hypertension after the ingestion of dietary tyramine After participating in this CME activity, the psychiatrist should be better able to: