McKenna's Pharmacology for Nursing, 2e

324

P A R T 4  Drugs acting on the central and peripheral nervous systems

Clinically important drug–food interactions Tyramine and other pressor amines that are found in food, which are normally broken down by MAO enzymes in the GI tract, may be absorbed in high con­ centrations in the presence of MAO inhibitors, resulting in increased blood pressure. In addition, tyramine causes the release of stored noradrenaline from nerve termi­ nals, which further contributes to high blood pressure and hypertensive crisis. People who take MAO inhib­ itors should avoid the tyramine-containing foods listed in Table 21.3. Prototype summary: Phenelzine Indications: Treatment of people with depression who are unresponsive to other antidepressive therapy or in whom other antidepressive therapy is contraindicated. accumulate in the synaptic cleft; this accumulation is thought to be responsible for the clinical effects. Pharmacokinetics: Route Onset Duration Oral Slow 48–96 hours T 1/2 : Unknown; metabolised in the liver, excreted in urine. Actions: Irreversibly inhibits MAO, allowing noradrenaline, serotonin and dopamine to Adverse effects: Dizziness, vertigo, headache, overactivity, hyperreflexia, tremors, mania, weakness, drowsiness, fatigue, sweating, orthostatic hypotension, constipation, diarrhoea, dry mouth, oedema, anorexia, potential for hypertensive crisis.

include nausea, vomiting, diarrhoea or constipation, anorexia, weight gain, dry mouth and abdominal pain. Urinary retention, dysuria, incontinence and changes in sexual function may also occur. Cardiovascular effects can include orthostatic hypotension, arrhythmias, pal­ pitations, angina and the potentially fatal hypertensive crisis. This last condition is characterised by occipital headache, palpitations, neck stiffness, nausea, vomiting, sweating, dilated pupils, photophobia, tachycardia and chest pain. It may progress to intracranial bleeding and fatal stroke. MAO inhibitors are associated with discontinu­ ation symptoms on cessation of therapy. Symptoms include agitation, irritability, ataxia, movement dis­ orders, insomnia, drowsiness, vivid dreams, cognitive impairment and slowed speech. Symptoms occasionally experienced when discontinuing MAO inhibitors include hallucinations and paranoid delusions. If possible MAO inhibitors should be withdrawn slowly. Clinically important drug–drug interactions Drug interactions of MAO inhibitors with other anti­ depressants include hypertensive crisis, coma and severe convulsions with TCAs and a potentially life-threatening serotonin syndrome with SSRIs. A period of 6 weeks should elapse after stopping an SSRI before beginning therapy with an MAO inhibitor. If MAO inhibitors are given with other sympa­ thomimetic drugs (e.g. methyldopa, guanethidine), sympathomimetic effects increase. Combinations with insulin or oral hypoglycaemic agents result in additive hypoglycaemic effects. People who receive these combi­ nations must be monitored closely, and appropriate dose adjustments should be made.

■■ TABLE 21.3 Tyramine-containing foods Foods high in tyramine

Foods with moderate amounts of tyramine

Foods with low amounts of tyramine

Aged cheeses: cheddar cheese, blue cheese, Swiss cheese, Camembert Aged or fermented meats, fish or poultry: chicken pâté, beef liver pâté, caviar Brewer’s yeast, Vegemite, Marmite, Bonox Broad beans Red wines: Chianti, burgundy, sherry, vermouth Soy sauce, tofu, banana peels Smoked or pickled meats, fish or poultry: herring, sausage, corned beef, salami, pepperoni

Meat extracts: consommé, bouillon Pasteurised light and pale beer Avocados

Distilled liquors: vodka, gin, Scotch, rye Cheeses: American, mozzarella, cottage cheese, cream cheese Chocolate Fruits: figs, raisins, grapes, pineapple, oranges Sour cream Yoghurt