MONOAMINE-OXIDASE INHIBITORS - AN UPDATE ON DRUG-INTERACTIONS

After initial enthusiasm, the use of monoamine oxidase inhibitors (MAO Is) has been limited by the wide range of MAOI-drug and MAOI-food inte ractions that are possible, particularly with sympathomimetic medicati ons or tyramine-containing foods, resulting in hypertensive reactions, Despite their clinical benefits, this has led to a reduction in use o f such medications. Discovery of the 2 main subgroups of monoamine oxi dase, types A and B, led to the synthesis of MAOIs selective for one o r other of these isoenzymes, Consequently, selegiline (deprenyl), a se lective MAO-B inhibitor, was developed for the treatment of idiopathic Parkinson's disease, This drug is useful in the treatment of the earl y stages of the disease and later on as an adjunct to other drug thera pies, Although the selective MAO-A inhibitor, clorgiline (clorgyline), was found to be effective in the treatment of depression, it still re tained the potential to cause hypertensive reactions. Recently, agents that are not only selective, but reversible in their inhibition of MA O-A (RIMAs) have been synthesised (e,g, moclobemide and toloxatone), a nd have proven antidepressant efficacy. Whilst they are less likely to induce hypertensive reactions with the concomitant administration of sympathomimetic drugs or with tyramine-rich foodstuffs, it still seems wise to advocate care in co-prescribing potentially interacting medic ations and to advise a degree of caution with regard to the dietary in take of foodstuffs likely to contain a high tyramine content. Although these newer drugs represent an advance in safety, their use has, as y et, only been established in the treatment of depression. RIMAs also r etain a potential for adverse interaction with other drugs. Concomitan t prescription of serotonin-enhancing drugs should only be undertaken with caution for patients on moclobemide, toloxatone or selegiline. Co prescription of sympathomimetic drugs should also be avoided with thes e newer MAOIs and patients should be advised against purchasing over-t he-counter preparations that may contain sympathomimetic drugs.