EMQs in Clinical Medicine.pdf - Peshawar Medical College

Adverse drug reactions – answers 239
H
-Adrenoceptor receptor blockade by a -adrenoceptor antagonist
( blocker) can cause symptoms of cold peripheries and impotence,
which may affect compliance. All -adrenoceptor antagonists are
contraindicated in patients with asthma as a result of the risk of
airway obstruction.
Blockers have a role in many aspects of cardiovascular disease, including
treatment of hypertension, angina and arrhythmias.
Blockers can also be used under specialist control for the treatment of
heart failure.
94 Adverse drug reactions
Answers: N C L A I
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A 21-year-old woman treated with medication for migraine develops
acute dystonia.
Acute dystonic reactions (including oculogyric crises) are recognized
adverse effects of metoclopramide. These reactions are more common
in the young.
Metoclopramide is a dopamine receptor antagonist that acts centrally on
the chemoreceptor trigger zone (CTZ). It also acts directly on the gastrointestinal
tract to prevent vomiting by enhancing gastric emptying.
A 35-year-old man on treatment for depression complains of a severe
throbbing headache soon after his evening meal. Blood pressure is
markedly raised.
This is a presentation of a ‘cheese’ reaction. Many foods, e.g. cheese and
yeast products, contain tyramine which is normally metabolized by
monoamine oxidases in the gut wall and liver. However, phenelzine is a
monoamine oxidase inhibitor and thus allows a larger amount of
tyramine to reach the systemic circulation. Tyramine is a sympathomimetic
and, therefore, the potentiation of this action by monoamine
oxidase inhibition can give rise to an acute hypertensive crisis. The
treatment of choice is intravenous phentolamine (-adrenoceptor
antagonist).
Reversible monoamine oxidases (reversibly inhibit monoamine oxidase
type A) are available, e.g. meclobemide, which are claimed to cause less
potentiation of the tyramine effect. However, patients should be
counselled very carefully regarding the avoidance of tyramine-rich food
when prescribed either class of drug.
A 34-year-old woman suffers from haemorrhagic cystitis after
receiving medication for systemic lupus erythematosus (SLE).
Cyclophosphamide is a potent cytotoxic drug that can be used to induce
remission of severe flares of SLE.