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| Monoamine oxidase inhibitors |
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Written by Helen Marshall, pharmacist
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Monoamine oxidase inhibitors (MAOIs) are one of the oldest
classes of antidepressants and are typically used when other antidepressants
have not been effective. They are used less frequently because they often
interact with certain foods and require strict dietary restrictions. MAOIs can
also result in severe adverse reactions if taken with many other medicines,
including some over-the-counter cough and cold remedies. MAOIs are mostly used
for atypical depression.
A newer type of MAOI called moclobemide is slightly different to
the older MAOIs. It is considered to be a safer choice than the older MAOIs, as
it requires fewer dietary restrictions and has fewer significant interactions
with other medicines. Moclobemide is considered a second-line treatment for
major depression.
How do MAOIs work?
It is thought that depression may be linked to an imbalance of
chemicals within the brain.
Within the brain there are chemical messengers or
neurotransmitters, called monoamines. Examples of these are noradrenaline and
serotonin.
Neurotransmitters are involved in controlling or regulating
bodily functions, and noradrenaline and serotonin are involved in the control
and regulation of mood.
When depression occurs, there may be a decrease in the amount of
these monoamines released from nerve cells in the brain. Monoamines are broken
down by a chemical (enzyme), called monoamine oxidase.
MAOIs prevent monoamine oxidase from breaking down the
monoamines. This results in an increased amount of active monoamines in the
brain.
By increasing the amount of monoamines in the brain, the
imbalance of chemicals, thought to be important in causing depression, is
altered. This helps relieve the symptoms of depression.
Moclobemide is a more selective type of MAOI, called a
reversible inhibitor of monoamine oxidase type A (RIMA). It works specifically
on monoamine oxidase type A, which gives it its slightly different profile.
How long do MAOIs take to work?
MAOIs can take a while to have an effect so you may not feel
better immediately when you start treatment with one.
You may experience an effect on your mood within two weeks,
however, the full benefits of treatment with MAOIs may not occur for a further
two to four weeks.
If you feel your depression has got worse, or if you have any
distressing thoughts or feelings in these first few weeks, then you should talk
to your doctor.
How long will I have to take them for?
MAOIs usually help mood improve over a number of weeks or
months. Even when things seem back to normal, you should keep taking them for a
further six months to minimise the chances of the depression coming back.
Are they addictive?
No. It is possible for MAOIs to produce unpleasant withdrawal
symptoms (sometimes called a discontinuation syndrome) when they are stopped.
But this is temporary, does not involve a craving for the medication, and can
usually be avoided if the drug is tapered off rather than stopped
suddenly.
This is not addiction. Withdrawal symptoms may include nausea,
headache, insomnia, giddiness, vivid dreams, agitation and irritability.
These can sometimes occur if you miss a dose of the
antidepressant, which is why it is important to take them as directed by your
doctor.
When stopping treatment withdrawal symptoms can be minimised or
avoided if the dose of the MAOI is gradually decreased over a period of a few
weeks. Your doctor will help you do this.
Which one is best for me?
There are three older, non-selective MAOIs; isocarboxazid,
phenelzine and tranylcypromine. These have similar cautions and side effect
profiles, though tranylcypromine is used the least frequently of the three
because it has a stimulant action that makes it more hazardous and most likely
to cause withdrawal symptoms on stopping treatment.
MAOIs should not be used in pregnancy and must not be given at
the same time as other antidepressants, as this can result in severe adverse
effects.
People taking MAOIs must avoid consuming foods that contain high
levels of the amino acid tyramine, as this can cause a dangerous rise in blood
pressure. There is more information in the factsheets about the individual
MAOIs linked below, but some examples of foods that need to be avoided while
taking these medicines are mature cheeses, pickled herring, broad bean pods, fermented
soya bean extract, yeast extract, eg Bovril, Oxo, Marmite and most alcoholic or low-alcohol drinks.
Certain medicines, especially over-the-counter cough and cold
remedies, need to be avoided when taking an MAOI, and there are many other
safety issues you need to be aware of relating to other conditions you might have
or medicines you might be taking.
For more detailed information on specific MAOIs click on the
relevant links below. The reversible inhibitor of monoamine oxidase type A,
moclobemide, is more likely to be used than these older MAOIs, because it is
believed to cause fewer food and drug interaction problems. However, as with
MAOIs some caution is still required with tyramine-containing foods and certain
medicines, especially over-the-counter cough and cold remedies.
Moclobemide is used as a second-line treatment for major
depression and also for the treatment of social phobia. There is more detailed
information in the factsheets linked below.
MAOIs
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Isocarboxazid
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Nardil (phenelzine)
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Tranylcypromine
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Last updated 21.03.2007
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