Food-drug interactions, MAOIs

One serious adverse reaction associated with the use of the MAOIs is hypertensive crisis (extremely high blood pressure), which may occur when foods containing tyramine (an amino acid present in some foods) are eaten (see Home Care Checklist Avoiding Drug Food Interactions With MAOIs). 

AVOIDING DRUG-FOOD INTERACTIONS WITH MAOIs... 

If the patient is prescribed an MAOI, it is critical that the nurse give the patient a list of foods containing tyramine. When teaching the patient, the nurse emphas zesthe importance of not eating any of the foods on the list. (See Home Care Checklist Avoiding Drug-Food Interactions With MAOIs)... 

Hypertensive crisis often occurs as a result of the interaction of two or more drugs acting via different mechanisms to potentiate the cardiovascular effects of NE. It can also occur as a result of a drug-food interaction involving MAOIs and tyramine-containing foods. Like the serotonin syndrome, hypertensive crisis can be fatal. Prodromal symptoms include the following ... 

MAOIs are effective, but physicians do not prescribe them often because they have potentially serious side effects from drug-drug and drug-food interactions. 

Monoamine Oxidase Inhibitors (MAOIs). Early studies also evaluated the effectiveness of the MAOl phenelzine. Phenelzine, relative to TCAs, provided greater benefit for PTSD however, its usefulness is limited by its potential for drug and food interactions. A recent open label study suggests that the reversible MAOI moclobemide might be helpful for PTSD. It is not available in the United States. 

The most common reason for the underutilization of MAOIs is the potential for serious consequences of MAOI drug-food and drug-drug interactions. Combined MAOI treatment with (1) foods or medications involved in monoamine synthesis (2) monoamines themselves or (3) other sympathomimetics routinely found in over-the-counter medications can result in hy-peradrenergic crises or serotonin toxicity (Blackwell, 1991). 

When explaining possible medication and/or food interactions, for example the importance of avoiding alcohol with certain drugs such metronidazole or cheese with monoamine oxidase inhibitors (MAOIs). 

The high incidence of drug-food and drug-drug interactions rule out MAOIs as antidepressants of first choice. However, there are circumstances in which these agents may be used effectively and successfully. These are ... 

The main problems with early, irreversible MAOIs were adverse interactions with other drugs (notably sympathomimetics, such as ephedrine, phenylpropanolamine and tricyclic antidepressants) and the infamous "cheese reaction". The cheese reaction is a consequence of accumulation of the dietary and trace amine, tyramine, in noradrenergic neurons when MAO is inhibited. Tyramine, which is found in cheese and certain other foods (particularly fermented food products and dried meats), is normally metabolised by MAO in the gut wall and liver and so little ever reaches the systemic circulation. MAOIs, by inactivating this enzymic shield, enable tyramine to reach the bloodstream and eventually to be taken up by the monoamine transporters on serotonergic and noradrenergic neurons. Fike amphetamine, tyramine reduces the pH gradient across the vesicle membrane which, in turn, causes the vesicular transporter to fail. Transmitter that leaks out of the vesicles into the neuronal cytosol cannot be metabolised because... 

One drawback to MAOI therapy is that the therapeutic benefit typically does not begin until after the third week of treatment at the earliest. This is, of course, generally true of all antidepressants that are used to treat panic disorder and other anxiety syndromes. Of greater concern are the potentially dangerous food and drug interactions of the MAOIs (cf. Chapter 3), which have relegated the use of MAOIs for those panic disorder patients who do not respond to other treatments. 

Some chemical exposures may be hepatic enzyme inducers/inhibitors, altering the effects of drugs like warfarin. Some foods such as mono-amines, will cause reactions in patients given MAOIs grapefruit juice may interact with terfenadine and some other drugs. New diseases may cause problems heart failure causing reduced liver blood flow can reduce the metabolism of drugs like warfarin. 

Not long after their introduction, it was discovered that MAOIs could have serious and sometimes fatal interactions with other medications and foods that have high levels of tyramine. Tyramine is found in foods like cheese, wine, beer, liver, and even chocolate, and can increase blood pressure. MAOIs interact with certain medications and foods, raising blood pressure so much that fatal results can occur. To be used safely, these drugs must be taken with a restricted diet. 

Newer MAOI drugs are selective for the MAO-A subtype of the enzyme, and are less likely to interact with foods or other drugs. Monoamine oxidase (MAO) inactivates monoamine substances, many of which are, or are related to, neurotransmitters. The central nervous system mainly contains MAO-A, whose substrates are adrenaline (epinephrine), noradrenaline (norepinephrine), metanephrine, and 5-hydroxyti7ptamine (5-HT), whereas extra-neuronal tissues, such as the liver, lung, and kidney, contain mainly MAO-B which metabolises p-phenylethylamine, phenylethanolamine, o-tyramine, and benzylamine. 

Arguably the first modern class of antidepressants, monoamine oxidase inhibitors (MAOIs) were introduced in the 1950s but are now rarely used in clinical practice because of toxicity and potentially lethal food and drug interactions. Their primary use now is in the treatment of depression unresponsive to other antidepressants. However, MAOIs have also been used historically to treat anxiety states, including social anxiety and panic disorder. In addition, selegiline is used for the treatment of Parkinson s disease (see Chapter 28). 

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