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P A R T 4
Drugs acting on the central and peripheral nervous systems
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inhibitors should be withdrawn slowly.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.
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.
■■
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
Prototype summary: Phenelzine
Indications:
Treatment of people with depression
who are unresponsive to other antidepressive
therapy or in whom other antidepressive therapy is
contraindicated.
Actions:
Irreversibly inhibits MAO, allowing
noradrenaline, serotonin and dopamine to
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.
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.
