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Urticaria, angioedema and drug allergy
Acute urticaria settles within 6 weeks and is treated with a second-generation antihistamine; angioedema without hives points to ACE inhibitors or a hereditary deficiency — where antihistamines do not help; and most "penicillin allergies" are not true allergy.
Why it matters in the exam
The exam asks when anaphylaxis can be diagnosed, how chronic urticaria is treated and which work-up is enough, and what to do with a child who developed a rash during amoxicillin. Other questions describe lip swelling in a patient who has taken an ACE inhibitor for years.
The key point about penicillin: in most cases a supervised amoxicillin "challenge" is possible at low risk, and an unverified allergy label leads to broader, poorer antibiotics.
Further questions deal with choosing an antibiotic for a patient with an allergy label: a cephalosporin with a different side chain usually suits even after a mild penicillin rash, and cross-reactivity is rare. Questions on anaphylaxis mainly test recognition — two systems or low blood pressure after exposure — and immediate intramuscular adrenaline, not the tests that follow.
Key points
- Acute urticaria — second-generation antihistamine.
- Chronic urticaria — over 6 weeks; dose up to 4-fold, then omalizumab.
- Angioedema without hives — ACE inhibitor or C1 deficiency.
- Anaphylaxis — adrenaline into the thigh muscle at once.
- Most penicillin-allergy labels are wrong; challenge at low risk.
Summary table
| Condition | Presentation | Treatment | Exam note |
|---|---|---|---|
| Acute urticaria | Itchy wheals, each fading within 24 hours; viral infection, drug, food | Second-generation antihistamine (cetirizine, loratadine) | Usually no work-up is needed |
| Chronic urticaria | Over 6 weeks, usually spontaneous | Second-generation antihistamine up to 4 times the dose, then omalizumab | Basic work-up only: blood count, CRP or ESR |
| ACE-inhibitor angioedema | Lip or tongue swelling without hives; even after years of treatment | Stop the drug; never return to ACE inhibitors | Antihistamines and adrenaline work less well |
| Hereditary angioedema | Recurrent attacks, abdominal pain, no hives | C1 inhibitor concentrate or icatibant | Low C4 |
| Anaphylaxis | Skin or mucosa together with breathing difficulty or low blood pressure; or two systems after exposure | Adrenaline 0.5 mg into the thigh muscle in an adult (0.01 mg/kg in a child), repeat after 5–15 minutes | An antihistamine does not replace adrenaline |
| "Penicillin allergy" | Rash in childhood, gastrointestinal effect | At low risk — oral amoxicillin challenge | Fewer than 10% of those reporting it are truly allergic |
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Sources
- EAACI/GA2LEN/EuroGuiDerm/APAAACI, 2022 — International guideline for the definition, classification, diagnosis and management of urticaria
- AAAAI/ACAAI Joint Task Force on Practice Parameters, 2022 — Drug allergy: a 2022 practice parameter update
- World Allergy Organization, 2020 — Anaphylaxis guidance
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.
See also: Anaphylaxis and angioedema in the emergency department