Adverse Drug Reactions
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Educational material; no clinical peer review is claimed. Methodology and limitations
An adverse drug reaction (ADR) is an unwanted, harmful response to a medicine taken at normal doses. Recognising an ADR and acting on it is a core pharmacist skill. This article is educational and does not replace formal pharmacovigilance training.
Why this matters in pharmacy
The pharmacist is often the first to hear about a suspected reaction. Spotting it early, distinguishing a true ADR from a symptom of the underlying illness, and routing the report correctly prevents repeat harm in the same patient and in others.
Types of ADRs
Type A reactions are dose-dependent and predictable from the pharmacology (e.g., beta-blocker bradycardia, NSAID gastric irritation). Type B reactions are unpredictable and independent of dose (e.g., penicillin allergy, statin-induced myopathy in susceptible patients). Most community-pharmacy ADRs are Type A and often preventable through dose review and interaction checking.
High-alert drugs to watch
Some drugs carry a higher ADR burden: anticoagulants (bleeding), insulin and sulfonylureas (hypoglycemia), opioids (respiratory depression), NSAIDs (renal and gastric effects), and digoxin (toxicity, especially in renal impairment and hypokalemia). A patient on one of these who reports new symptoms warrants a structured ADR check.
Recognising an ADR at the counter
A new symptom that appears after a medicine was started or changed is a clue. Timing, dose relationship, and whether the symptom is known for that drug all help. An ADR does not require stopping the drug independently — the pharmacist's job is to recognise, document, and refer appropriately.
What the pharmacist does
Take a brief timeline: what started when, in relation to which medicine. If the reaction is serious (anaphylaxis, severe bleeding, angioedema, severe skin reaction), refer urgently. If mild and predictable, counsel the patient, document, and liaise with the prescriber about whether a dose change or alternative is needed. Do not advise stopping a prescribed medicine without prescriber involvement.
Red flags
Anaphylaxis (airway, breathing, circulation involvement), severe skin reactions with blistering or mucosal involvement, uncontrolled bleeding on an anticoagulant, severe hypoglycemia, and any reaction with systemic signs (fever, organ involvement) are emergencies. Refer immediately.
When to refer
Serious or severe reactions need urgent medical attention. Non-serious reactions should still be documented and reported to the prescriber and, where appropriate, to the national pharmacovigilance system. ADR reporting is how rare harms are detected after a drug reaches the market.
Practical example
Dizziness on a new antihypertensive
A patient started on a new antihypertensive two weeks ago reports dizziness on standing. The pharmacist recognises a likely Type A ADR (postural hypotension from the new drug), counsels on standing slowly and hydration, documents the timeline, and contacts the prescriber to discuss a dose adjustment rather than advising the patient to stop independently. The reaction is managed safely and reported.
Key takeaways
- Most community ADRs are Type A (dose-dependent and predictable) and often preventable.
- High-alert drugs (anticoagulants, insulin, opioids, NSAIDs, digoxin) carry a higher ADR burden.
- A new symptom after a medicine was started or changed is a key clue — take a timeline.
- Do not advise stopping a prescribed drug independently; recognise, document, refer, and report.
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