MAOIs Tyramine-rich foods

MAOIs Pharmacodynamic—hypertensive crisis Tyramine-rich foods Sympathomimetics... 

The answer is b. (Hardmanr p 444.) This patient ate tyramine-rich foods while taking an MAOI and went into hypertensive crisis. Tyramine causes release of stored catecholamines from presynaptic terminals, which can cause hypertension, headache, tachycardia, cardiac arrhythmias, nausea, and stroke. In patients who do not take MAOls, tyramine is inactivated in the gut by MAO, and patients taking MAOls must be warned about the dangers of eating tyramine-rich foods. 

After 5 to 10 days of use furazolidone has MAO-inhibitory activity about equivalent to that of the non-selective MAOIs. The concurrent use of furazolidone with indirectly-acting sympathomimetic amines (amfetamines, phenylpropanolamine, ephedrine, etc.) or with tyramine-rich foods and drinks may be expected to result in a potentially serious rise in blood pressure. However, direct evidence of accidental adverse reactions of this kind does not seem to have been reported. The pressor effects of noradrenaline (norepinephrine) are unchanged by furazolidone. 

Linezolid is a weak, non-selective inhibitor of MAO. As a consequence, it can inhibit the breakdown of the tyramine by MAO in the gut, and can also potentiate the effect of tyramine at nerve endings, therefore causing an increase in blood pressure (see Mechanism, under MAOIs or RIMAs + Tyramine-rich foods , p.ll53). However, the extent of this rise was similar to that for moclobemide, which is much less than that seen with classical MAOIs. 

The manufacturers of linezolid recommend that patients should avoid large amounts of tyramine-rich foods and drinks and should not consume more than 100 mg of tyramine per meal. For a list of the possible tyramine-content of various foods and drinks, see Table 32.2 , (p.ll52), Table 32.3 , (p.ll54) and Table 32.4 , (p.ll55). This is in line with the dietary restrictions recommended for RIMAs rather than the more stringent dietary recommendations required in patients taking non-selective MAOIs. 

In practical terms this means that patients taking moclobemide with selegiline should be given the same dietary restrictions for tyramine-rich foods and drinks (see tyramine-rich drinks , (p.l 151) and tyramine-rich foods , (p.l 153)), that relate to the non-selective MAOIs such as phenelzine and tranylcypromine. However, because of the potential risks the manufacturer of moclobemide contraindicate this combination. On the basis of work done on the pig it is suggested that if selegiline is replaced by moclobemide, the dietary restrictions can be relaxed after a wash-out period of about 2 weeks. If switching from moclobemide to selegiline, a wash-out period of 1 to 2 days is sufficient. ... 

Monosodium glutamate alone can cause a small rise in blood pressure, and MAOIs alone very occasionally cause hypertensive episodes. However, the reactions reported with soy sauce and chicken nuggets were probably due to a high tyramine content, as a high tyramine content has subsequently been detected in some soy sauces, (see also MAOIs or RIMAs + Tyramine-rich foods , p.ll53). 

Hypertensive reactions have been controlled by intravenous phen-tolamine, phenoxybenzamine, intramuscular chlorpromazine, labetalol or sublingual nifedipine. The manufacturers of phenelzine state that on the basis of present evidence, slow intravenous injection of phentolamine is recommended. However, it is advisable to refer to current guidelines on the management of hypertensive crises for up-to-date advice. See also Importance and Management under MAOIs or RIMAs + Tyramine-rich foods , p.II53. 

An extremely well-documented, well-established, serious interaction. A potentially fatal hypertensive reaction can occur between the irreversible, non-selective MAOIs (see Table 32.1 , (p.ll30)) and tyramine-rich foods. Tranylcypromine is more likely to cause the reaction than phenelzine. The incidence is uncertain, but early estimates of hypertensive reactions to tranylcypromine (before restrictions in its use with indirectly-acting sympathomimetics and foods) range from 0.03% to 20%. Patients taking any of the non-selective MAOIs (isocarboxazid, niaiamide. 

A 77-year-old woman with hiatus hernia, who had been taking cimetidine 400 mg four times daily for 3 years, experienced a severe frontal headache and hypertension, which appeared to be related to the ingestion of a cup of Bovril and some English cheddar cheese, both of which can contain substantial amounts of tyramine. Although the authors point out the similarity between this reaction and that seen in patients on MAOIs who eat tyramine-rich foods (see MAOIs or RIMAs + Tyramine-rich foods , p. 1153), there is no satisfactory explanation for what occurred. They note that she was also taking salbutamol (another sympathomimetic) but rule out any contribution from this drug. 

The monoamine oxidase inhibitors (MAOIs) work through augmented activity of dopamine, as monoamine oxidase normally degrades norepinephrine and serotonin. The MAOIs are rarely used clinically due to their adverse effects, notably orthostatic hypotension, peripheral edema, myoclonic jerks, weakness, and insomnia. Hypertensive crisis can result when combined with sympathomimetics, including over-the-counter products such as ephe-drine and pseudoephedrine. Further, MAOIs are known to contribute to the serotonin syndrome and use of meperidine must be avoided in such patients. Patients on MAOI need to restrict tyramine-rich foods, as well [1,2]. 

The "cheese effect" is a well-established phenomenon whereby an amine-rich food is consumed while the patient is being treated with an irreversible MAOI. Foods which cause such an effect include cheeses, pickled fish, yeast products (red wines and beers, including non-alcoholic varieties), chocolate and pulses such as broad beans (which contain dopa). It appears that foods containing more than 10 mg of tyramine must be consumed in order to produce a significant rise in blood pressure. Furthermore, it is now apparent that there is considerable variation in the tyramine content of many of these foods even when they are produced by the same manufacturer. Therefore it is essential that all patients on MAOIs should be provided with a list of foods and drinks that should be avoided. 

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