EMQs in Clinical Medicine.pdf - Peshawar Medical College

Adverse drug reactions – answers 237
92 Adverse drug reactions
Answers: E B J M G
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A 35-year-old woman presents with polyuria and polydipsia. She
says that she is on medication for bipolar disorder.
Polyuria and polydipsia are suggestive of diabetes insipidus. Lithium is
a well-recognized drug cause of nephrogenic diabetes insipidus.
Lithium has a narrow therapeutic window and so therapeutic drug
monitoring is very important. Signs of toxicity include tremor, ataxia
and dysarthria.
A 25-year-old man on anti-TB therapy complains of orange
discoloration of the urine.
Rifampicin can cause bodily secretions, such as saliva, tears and urine, to
be coloured orange–red. Rifampicin is a potent cytochrome P450 inducer
and thus has the potential to reduce plasma levels of cytochrome P450
substrates. If a drug is prescribed with rifampicin, the dose needs to be
increased to compensate.
A 56-year-old man complains of a persistent dry cough a few weeks
after starting new anti-hypertensive medication.
Angiotensin-converting enzyme (ACE) (also known as kininase II)
converts inactive angiotensin I to the vasoconstrictor angiotensin II. In
this way, ACE inhibitors reduce angiotensin II levels.
ACE also inactivates bradykinin and so ACE inhibitors may cause a
persistent dry cough resulting from increased levels of bradykinin.
A 50-year-old woman complains of a metallic taste in the mouth and
anorexia after starting medication for her diabetes.
Metformin is particularly useful in treating overweight patients with type
2 diabetes mellitus because of its anorectic effect (sulphonylureas can
encourage weight gain). Metformin reduces glucose absorption from the
gut, inhibits liver gluconeogenesis and increases uptake of glucose into
tissues. Hypoglycaemia does not usually occur with metformin treatment.
Lactic acidosis is a very rare complication of metformin treatment but
carries a high mortality. Metformin is therefore contraindicated in
patients who are at risk of lactic acidosis, e.g. significant renal impairment.
Metformin should be replaced with insulin before elective surgery.
A 55-year-old woman presents with weight gain, hypertension and
proximal myopathy.
The use of corticosteroids can give rise to an iatrogenic Cushing’s
syndrome. Therefore, long-term adverse effects of steroid treatment
include diabetes, osteoporosis and hypertension.