Adverse drug reactions and pharmacovigilance — formative SAQs

SAQ 1 — Classification and causality (10 marks, 15 minutes)

Question. Define an adverse drug reaction and distinguish it from an adverse drug event and a medication error. Outline the Rawlins and Thompson classification (Type A and Type B) and the DoTS extension, and explain how you would apply the Naranjo algorithm to assess causality in a child with a suspected reaction. ^[2]

Model answer — a full-marks answer names the definitions, the contrast, and the operational tool. ^[1]

1. Definition of an ADR (1 mark). A noxious and unintended response to a medicine that occurs at doses normally used in humans. The phrase "normally used" is essential — it excludes overdose and error.
2. Distinction from an ADE and a medication error (2 marks). An adverse drug event is any harm from a medicine whether or not the dose was correct, so it captures both true ADRs and harm from medication errors. A medication error is the process failure itself (wrong drug, dose, route, time or patient) that may or may not reach the child and may or may not cause harm.
3. Rawlins and Thompson classification (3 marks). Type A (augmented): an exaggerated primary pharmacological effect that is predictable, dose-related, common, and usually of low mortality (for example opioid respiratory depression, beta-agonist tachycardia). Type B (bizarre): a qualitatively abnormal response that is unpredictable, largely dose-independent, rare, and potentially lethal; it is immune-mediated (anaphylaxis, SJS/TEN, DRESS) or idiosyncratic (G6PD haemolysis). Mention the alphabet extension: Type C chronic, Type D delayed, Type E end-of-use (withdrawal), Type F failure of therapy.
4. DoTS extension (2 marks). DoTS classifies each reaction across three axes — Dose-relatedness (standard, low or high), Time-relatedness (early, intermediate, late or cumulative), and Susceptibility (age, genotype, organ function, disease, interacting drugs). It complements Type A/B by explaining mixed patterns.
5. Naranjo application (2 marks). Score the ten items (previous conclusive reports, temporal relationship to the suspected drug, improvement on withdrawal, recurrence on rechallenge, alternative causes, placebo response, drug detected in blood, dose-dependent reaction, prior exposure, objective confirmation). Sum and band the score: 0 to 4 doubtful, 5 to 6 possible, 7 to 13 probable, 14 to 18 definite. ^[1]