Reasoning GP · Algorithm · 1-page summary
Maculopapular rash
For: adults and children with a new widespread red macular or papular rash, in hours or OOH. Not for: urticaria alone or a non-blanching rash as the main finding (use the urticaria and purpura/petechiae pathways). Pregnancy and children with persistent fever go straight to block 2.
Core rule: look at the mucosae and the patient, not just the skin. Skin pain, blistering, mucosal involvement or systemic upset means SJS/TEN, DRESS or sepsis — stop the drug and escalate. A blanching rash can be early meningococcaemia.
0Stop — call 999 now — first 60 seconds: sick or well, ABC, temperature, BP, mucosae
- Fever and seriously ill, meningococcal features or a rapidly evolving rash → 999 even if the rash blanches or is absent. Do not wait for petechiae or purpura.
- Skin pain, blistering or detachment, mucosal involvement (eyes, mouth, genitals) + fever (SJS/TEN) → stop the suspected culprit drug + Same-day hospital (usually admission); 999 if critically unwell, shock or cannot travel safely; urgent ophthalmology if eyes involved.
- Rash with shock, altered consciousness or respiratory compromise, including anaphylaxis → 999
- While waiting: suspected meningococcal disease → IV/IM ceftriaxone or benzylpenicillin as soon as possible unless it would delay transfer; none if severe allergy to either. Phone the Health Protection Team. No steroids, ciclosporin or IVIG in primary care.
1Triage by drug timing — new drugs with start dates (CG183)
| Onset after drug | Think |
|---|---|
| Minutes–hours | Urticaria or anaphylaxis (immediate reaction) |
| 6–10 days | Maculopapular drug eruption (≤3 days on re-exposure) |
| 7–14 days | SJS/TEN window: check mucosae, skin pain, blisters → block 0 |
| 2–6 weeks | DRESS (can be later) → block 2 |
2Screen — one row is enough
- DRESS: drug rash + fever, facial oedema, nodes, eosinophilia or organ involvement (eosinophilia may be absent early) → stop drug, Same-day hospital
- Kawasaki: child, fever ≥5 days + conjunctivitis, strawberry tongue, cracked lips, nodes; think incomplete Kawasaki, MIS-C → Same-day paediatrics
- Palpable purpura + arthralgia, abdominal pain, haematuria → BP, urine, renal function. Severe abdominal pain, GI bleed, AKI, hypertension, neurology, testicular pain, systemically ill → Same-day hospital
- Measles (Koplik spots, cough, conjunctivitis, unimmunised) → isolate, phone the HPT on suspicion Same-day
- Pregnant, with a rash or rash contact → HPT / obstetric advice Same-day; investigate any rash illness (rubella, parvovirus B19, measles, chickenpox).
- Palms and soles, copper-coloured, nodes, mucosal patches → syphilis serology + HIV test → GUM same week
3Assess — phenotype-led
☐ Glass test (does not exclude meningococcal disease) ☐ Mouth, eyes, genitals; Nikolsky sign if blistering ☐ Nodes, spleen, facial oedema ☐ Drug, travel, sexual and vaccination history
Drug reaction → FBC + differential, LFTs, renal function; urine dip if vasculitis. Avoid routine EBV/CMV serology, ANA, specific IgE.
4Classify — only if blocks 0–2 are negative
- Viral exanthem (commonest) — measles, rubella, parvovirus (slapped cheek), roseola (rash as fever settles, age <3) → supportive.
- Drug eruption — symmetrical, itchy, trunk then limbs → consider stopping the drug; watch for severe features.
- EBV + amoxicillin — sore throat, nodes, splenomegaly. Drug–virus interaction, not penicillin allergy.
- Secondary syphilis / HIV seroconversion — palms and soles suggest, not diagnose; HIV 2–4 weeks after exposure → GUM.
- Inflammatory — pityriasis rosea (herald patch), eczema, psoriasis; SLE (malar), systemic JIA, dermatomyositis → rheumatology.
- Uncertain — say so; manage only if well with reliable follow-up, else dermatology.
5Treat today — only if well and none of blocks 0–2
- Viral: paracetamol or ibuprofen, emollient; cetirizine for itch. Avoid routine sedating antihistamines.
- Simple drug eruption: consider stopping the drug (specialist advice if essential); antihistamine, emollient ± topical steroid. No routine oral steroids.
- EBV-amoxicillin rash: stop amoxicillin; not penicillin allergy. Document (CG183): drug, dose, date, reaction, severity, allergy vs adverse effect; tell the patient in writing. Doses: NICE/SPC, BNF, local formulary.
6Refer
- Uncertain diagnosis when well, persistent or recurrent rash → Dermatology ≤1 week
- Severe or immediate reaction, or confirmation would change treatment → drug-allergy service. No drug challenge in primary care.
- Suspected SLE, JIA or dermatomyositis → rheumatology (paediatrics for children).
- Check MMR uptake (UKHSA Green Book); no MMR in pregnancy.
7Never reassure by
- A blanching rash or glass test in an unwell, febrile patient.
- Looking at the skin without the mouth, eyes and genitals.
- "Just a drug rash" without checking fever, facial oedema, nodes and eosinophils.
- A normal eosinophil count early in suspected DRESS.
- Waiting for laboratory confirmation before notifying measles.
- Waiting for bloods or echo in a child with possible Kawasaki disease.
8Safety-net — say it, then document it
999 “Call 999 if the spots stop fading when pressed with a glass and there is fever, or the skin becomes painful, blisters or peels, or the mouth, eyes or genitals are affected.” Same day: “Contact us today if a drug rash is worse 48 hours after stopping the drug, fever or swollen glands appear, or a child has a lasting fever with red eyes, lips or tongue. Severe tummy pain or blood in the stool — go to hospital today.”
Review: not improving at 1 week; drug rash reviewed at 1 week. Measles: isolation advice and contacts' vaccination checked.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies; systemically well
Rash blanches; mucosae checked; no skin pain, blisters or facial oedema
New drugs and start dates reviewed; culprit decision made
Reaction documented and coded; measles notified if suspected
Safety-net given; reliable follow-up arranged
Summary of the full Reasoning GP maculopapular rash algorithm, which holds the differentials, investigations and evidence. Sources: NICE CG183, NG240, NG143; BSACI drug allergy; UKHSA meningococcal, measles and viral rash in pregnancy guidance; Green Book chapters 21 and 28; BASHH syphilis 2024. Clinical reference — follow local emergency-transfer policies and check doses: NICE/SPC, BNF.