GPAtlas🧭 When to suspect
Suspect an adverse drug reaction (ADR) – an appreciably harmful or unpleasant reaction resulting from a medicinal product – whenever a patient develops new or unexpected symptoms after starting a drug, increasing a dose, or taking an over-the-counter or herbal remedy. ADRs are a common and important cause of hospital admission, and the presentation ranges from a mild rash or cough to a life-threatening emergency such as anaphylaxis or a severe cutaneous adverse reaction (SCAR).
The diagnostic anchor is a temporal relationship between the drug and symptom onset, supported where possible by improvement on stopping the drug (de-challenge) and recurrence on restarting it (re-challenge – rarely advisable in primary care). Maintain a high index of suspicion in older patients on polypharmacy, in whom an ADR is easily mistaken for a new illness.
| Type | Nature | Example |
|---|---|---|
| A – Augmented | Dose-related, predictable from pharmacology; common (~80%), low mortality | Bradycardia with beta-blockers; bleeding with anticoagulants; hypoglycaemia with sulfonylureas |
| B – Bizarre | Non-dose-related, unpredictable, uncommon; higher mortality | Penicillin anaphylaxis; SJS/TEN; idiosyncratic reactions |
| C – Chronic | Dose- and time-related (cumulative) | Adrenal suppression and osteoporosis with long-term corticosteroids |
| D – Delayed | Time-related; may appear long after exposure, even after stopping | Teratogenesis; tardive dyskinesia with antipsychotics; secondary malignancy |
| E – End-of-use | Withdrawal reaction on stopping | Benzodiazepine withdrawal; rebound hypertension; adrenal crisis on abrupt steroid cessation |
| F – Failure of therapy | Unexpected failure, often from an interaction | Reduced contraceptive efficacy with enzyme inducers (e.g. rifampicin, carbamazepine) |
The Rawlins–Thompson mnemonic – Augmented, Bizarre, Chronic, Delayed, End-of-use, Failure – is the classification used by the MHRA. The crucial split in practice is Type A (manage by reducing the dose) versus Type B (stop and avoid).
Source: MHRA
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