Treatment of Mood Disorders: Monoamine Oxidase Inhibitors
Monoamine oxidase inhibitors (MAOIs) are another class of antidepressant that is effective, but they possess other properties limiting their use in the depressed medically ill patient. The mode of action of MAOIs is determined by the specific receptor, either MAO-A or MAO-B, which they block. MAO-A degrades serotonin, norepinephrine, and epinephrine, whereas MAO-B degrades dopamine and phenylalanine. The most commonly prescribed agents of this class are phenelzine and tranylcypromine. Both phenelzine and tranylcypromine are nonspecific and effect both MAO-A and MAO-B receptors. Selegiline is another MAOI with specificity for the MAO-B receptor and is used for treatment in Parkinson’s disease. Currently selegiline lacks an indication for use in depression. Some anecdotal evidence suggests an antidepressant effect of selegiline, but this was at very high dosages, leading to the loss of receptor specificity and action on the MAO-A as well. Much of the difficulty with the use of these agents centers on complicating adverse interactions between the MAOI and other medications and/or compounds. The most widely recognized problem is the potential for tyramine-induced hypertensive crisis. This requires the patient to remain on a specific diet that prevents this adverse event. MAOIs can also interact and cause untoward and potentially fatal reactions from concomitant use with other antidepressants including SSRIs, anti-asthmatic agents, sympathomimetic agents, meperidine, levodopa, furazolidone, and oral hypoglycemics. More common with MAOIs is orthostatic hypotension, which often limits the use of MAOIs in the elderly and medically ill.