Adverse reactions: Introduction
NB: See learning outcomes for this tutorial mapped to competencies, a PDF of the whole text, and a one-page summary.
☞ Why this subject matters...
It is estimated that 1 in 16 hospital admissions are due to an adverse drug reaction (ADR), and they are responsible for 4% of hospital bed capacity. ADRs themselves are also thought to occur in 10-20% of hospitalised inpatients, and one study found that over 2% of patients admitted with an ADR died, approximately 0.15% of all patients admitted.
Statistics from hospital medicines helplines for patients show that a high proportion of calls are concerned with side effects.
In practice, pharmacists encounter many clinical problems concerning adverse reactions such as:
- Can drug X cause symptom Y? Is it reversible?
- Which of drugs A, B or C is the most likely cause of symptom Y?
- How should I manage a suspected ADR in this patient?
- This patient has experienced a suspected reaction to drug X. What can I use instead?
Definition
ADRs are great mimickers of disease, causing diagnostic confusion and resulting in unnecessary referral and investigation. Certain disorders are commonly drug-induced, and a thorough assessment of drug exposure is particularly important in these cases. Examples of signs and symptoms include rashes, electrolyte disturbances, postural hypotension, confusion, constipation, renal or liver dysfunction, and gastrointestinal haemorrhage. Less common examples include blood dyscrasias.
What's the difference between a sign and a symptom? ➔ Consider, then click for answer.
A symptom is something that a patient notices and complains of (e.g. headache, thirst); it is subjective evidence. A sign is something objective picked up by examination or investigation (e.g. increased plasma creatinine, splenomegaly).
Shortly, we'll be looking at causality – how to assess whether a medicine is responsible for your patient's symptoms rather than something else. But first, we need to be sure that we are all talking about the same thing when we describe an ADR.
What are the essential features of an ADR? ➔ Consider, then click for answer.
ADRs are also known as side effects, and have these characteristics:
– There is some evidence that at least one medicine is responsible.
– The effect is unintended.
– It is harmful, or potentially harmful.
– The reaction is seen at normal doses used clinically (to distinguish ADRs from ‘toxicity’ which describes signs and symptoms of overdose or poisoning).
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