Food interactions, monoamine oxidase

Levodopa interacts with many different drugs. When levodopa is used with phenytoin, reserpine, and papaverine, there is a decrease in response to levodopa The risk of a hypertensive crisis increases when levodopa is used with the monoamine oxidase inhibitors (see Chap. 31). Foods high in pyridoxine (vitamin B6) or vitamin B6 preparations reverse the effect of levodopa However, when carbidopa is used with levodopa, pyridoxine has no effect on the action of levodopa hi fact, when levodopa and carbidopa are given together, pyridoxine may be prescribed to decrease the adverse effects associated with levodopa... 

FIGURE 29-2. Levodopa absorption and metabolism. Levodopa is absorbed in the small intestine and is distributed into the plasma and brain compartments by an active transport mechanism. Levodopa is metabolized by dopa decarboxylase, monoamine oxidase, and catechol-O-methyltransferase. Carbidopa does not cross the blood-brain barrier. Large, neutral amino acids in food compete with levodopa for intestinal absorption (transport across gut endothelium to plasma). They also compete for transport across the brain (plasma compartment to brain compartment). Food and anticholinergics delay gastric emptying resulting in levodopa degradation in the stomach and a decreased amount of levodopa absorbed. If the interaction becomes a problem, administer levodopa 30 minutes before or 60 minutes after meals. 

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. 

MAOIs work by inhibiting a brain enzyme called monoamine oxidase. Patients taking MAOIs must avoid a substantial list of foods that can interact with the medication and cause dangerously high blood pressure. 

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). 

Monoamine oxidase inhibitors (eg, tranylcypromine, phenelzine) are older antidepressants that are occasionally used for resistant depression. They can cause severe hypertensive reactions when interacting foods or drugs are taken (see Chapters 9 and 30), and they can interact with the selective serotonin reuptake inhibitors (SSRIs). 

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

S.B. Lipman, and K. Nash, Monoamine oxidase inhibitor update Potential adverse food and drug interactions. Drug Safety 5 195-204, 1990. 

The monoamine oxidase inhibitors epitomize cyclical fashions in drug use and the impact of adverse effects. They were the first psychotropic drugs for which a clear biochemical action was defined. Early excitement was quickly tempered by reports of liver toxicity with the hydrazine derivatives, leading to synthesis of the cyclopropylamine drug, tranylcypromine, which in turn elicited the food and drug interactions that led to an overall decline in popularity. 

Procarbazine is a weak inhibitor of monoamine oxidase adverse drug and food interactions can occur, for example with tyramine-containing foods and drinks,... 

Fnrazohdone is used in the treatment of giardiasis. Its adverse effects are usually mild and transient abdominal discomfort, nausea, and vomiting. The urine may be dark-colored (SEDA-11, 597). Metabolites of furazolidone inhibit monoamine oxidase (1) and there is therefore the potential for interactions with foods containing tyramine (2) and with opioid analgesics hyperpyrexia has been reported in rabbits that were given fnrazohdone and pethidine (3). 

Phentolamine is a non-selective alpha-adrenoceptor antagonist. It is used to treat hypertensive crises attributable to the effects of noradrenahne, as in pheochromo-cytoma and during the interaction of monoamine oxidase inhibitors with amine-containing medicaments and foods (1). Its adverse effects are similar to those of phenoxy-benzamine. 

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). 

Administered as a single, daily dose on an empty stomach Monoamine oxidase inhibitors drug-food interactions with tyramine-rich foods such as red wines, dark beers, aged cheeses, yogurt may precipitate hypertensive crisis drug interactions tricyclic antidepressants and SSRIs, sympathomimetics disulfiram-like reaction with alcohol... 

The modest improvements achieved in selectivity with respect to serotonin reuptake inhibition may also have been achieved with an isoenzyme system. Moclobemide, which was introduced in Sweden, reversibly inhibits monoamine oxidase A (RIMA). It is likely that this eliminates the severe hypertensive drug and food interactions that so severely limit the usefulness of the very effective earlier MAO inhibitors, since tyramine is now metabolized. An additional benefit of such agents may be a lack of cholinergic and cardiovascular effects. 

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