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Cutaneous drug reactions — DRESS, AGEP and fixed drug eruption
Every cutaneous drug reaction is identified by the "time window" between starting the drug and onset of the rash and by warning signs; a simple maculopapular rash appears after 4–14 days, AGEP after 1–2 days, DRESS after 2–8 weeks, and a fixed drug eruption recurs at the same site within hours.
Why it matters in the exam
The exam shows a patient who, three weeks after starting allopurinol, carbamazepine, lamotrigine or a sulfonamide, develops fever, a widespread rash, facial oedema, enlarged nodes, eosinophilia and liver injury — DRESS. Or a patient who, two days after a beta-lactam antibiotic, develops dozens of small non-follicular pustules on a red background in the folds — AGEP. Or a round violaceous-brown patch that recurs at the same site on the lip or genitals after every dose of NSAIDs or tetracycline — fixed drug eruption. The question tests the distinction, the first step — stopping the drug — and the treatment: prolonged systemic steroids in DRESS with a slow taper, and supportive care in AGEP. Also asked are HLA-B*58:01 before allopurinol and HLA-A*31:01 before carbamazepine. Remember that in DRESS organ injury can appear or worsen weeks after the rash, that liver, kidney and thyroid function must be followed, and that there is a later risk of autoimmune disease, including thyroiditis and diabetes.
Key points
- The time between starting the drug and onset of the rash is the most important clue to the reaction type.
- DRESS appears 2–8 weeks after the drug with fever, facial oedema, nodes, eosinophilia and organ injury.
- DRESS is treated by stopping the drug at once and giving systemic steroids with a slow taper and long follow-up.
- AGEP appears within 1–2 days, mainly after beta-lactams, and clears when the drug is stopped.
- A fixed drug eruption recurs at the same site after every exposure, mainly to NSAIDs and tetracyclines.
Summary table
| Reaction | Time from starting the drug | Picture | Treatment and triggering drugs |
|---|---|---|---|
| Maculopapular (morbilliform) rash | 4–14 days | Measles-like rash, itch, no systemic signs | Stop or continue with caution; topical steroids; aminopenicillins, sulfonamides |
| DRESS | 2–8 weeks | Fever, widespread rash, facial oedema, nodes, eosinophilia, liver and kidney | Stop at once, systemic steroids with slow taper; allopurinol, carbamazepine, lamotrigine, sulfonamides, vancomycin |
| AGEP | 1–2 days | Dozens of small non-follicular pustules on a red background, in folds, fever and neutrophilia | Stop and supportive care; clears in about two weeks; beta-lactams, macrolides, hydroxychloroquine |
| Fixed drug eruption | Hours after re-exposure | Round violaceous-brown patch, sometimes a blister, at the same site — lips, genitals | Stop; leaves pigmentation; NSAIDs, tetracyclines, sulfonamides, paracetamol |
| SJS/TEN (for comparison) | 4–28 days | Dusky lesions, blisters, skin detachment, mucosa | Burns unit; see the SJS/TEN topic |
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Sources
- RegiSCAR scoring system for DRESS, 2013 — Diagnostic criteria
- British Association of Dermatologists guideline on the management of drug reaction with eosinophilia and systemic symptoms, 2024 — Treatment
- CPIC guideline for HLA genotype and use of carbamazepine and allopurinol, 2017 — HLA-B*58:01 and HLA-A*31:01
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.