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Section IVOther important drugswith extreme caution as they may also precipitate exaggerated hypertension. The
elective case presents potential difficulties. If MAOI therapy is withdrawn for the
required 14–21 days before surgery, the patient may suffer a relapse of their depres-
sion with potentially disastrous consequences. However, the newer agents may con-
trol depression more effectively and reduce the chance of a serious peri-operative
drug interaction.
Indirectly acting sympathomimetic amines are heavily dependent on MAO for
their metabolism and therefore may produce exaggerated hypertension and arrhyth-
mias when administered with an MAOI. The directly acting sympathomimetic
amines should also be used with caution although they are also metabolized by
COMT and therefore are not subject to the same degree of exaggerated response.
MAOIs should be stopped for 2 weeks before starting alternative antidepressant
therapy and 2 weeks should have elapsed from the end of tricyclic therapy to the
start of MAOI therapy.Atypical agents
Mianserin
Mianserin is a tetracyclic compound used in depressive illness, especially where
sedation is required. It does not block the neuronal re-uptake of transmitters in
contrast to the TCAs. It does, however, block presynapticα 2 -adrenoceptors, which
reduces their negative feedback, resulting in increased synaptic concentrations of
neurotransmitters.
Ithas very little ability to block muscarinic and peripheralα-adrenoceptors and
as such causes less in the way of antimuscarinic effects or postural hypotension.
Itsimportant side effects are agranulocytosis and aplastic anaemia, which are
more common in the elderly.Lithium carbonate
Lithium is used in the treatment of bipolar depression, mania and recurrent affective
disorders. It has a narrow therapeutic index and plasma levels should be maintained
at 0.5–1.5 mmol.l−^1 .Inexcitable cells, lithium imitates Na+and decreases the release
of neurotransmitters.
Itmay increase generalized muscle tone and lower the seizure threshold in epilep-
tics. Many patients develop polyuria and polydipsia due to antidiuretic hormone
antagonism. It may also produce raised serum levels of Na+,Mg^2 +and Ca^2 +.Lithium
prolongs neuromuscular blockade and may decrease anaesthetic requirements as it
blocks brain stem release of noradrenaline and dopamine.
The thyroid gland may become enlarged and underactive and the patient may
experience weight gain and tremor. Above the therapeutic level patients suffer with
vomiting, abdominal pain, ataxia, convulsions, arrhythmias and death.