Antihistamines & Urticaria
Introduction
Urticaria (hives) and angioedema are common emergency department (ED) presentations. H1‑antihistamines are the mainstay for symptomatic relief of histamine‑mediated cutaneous symptoms (pruritus, wheals, localized angioedema).
Emergency clinicians must rapidly distinguish isolated urticaria from anaphylaxis, prioritise life‑saving treatment, and understand the role and limits of antihistamines in acute and chronic disease.
This section summarises pharmacology, practical prescribing (including commonly used chlorphenamine dosing bands), emergency priorities, chronic‑urticaria escalation, safety cautions and exam‑relevant pitfalls. Where dosing is given, verify against BNF/SPC or local formularies before prescribing.
Classification and pharmacology - practical points
- H1‑antihistamines are divided into first‑generation (sedating; e.g., chlorphenamine) and second‑generation (non‑sedating; e.g., cetirizine, loratadine, fexofenadine).
- Second‑generation agents are preferred first‑line for most patients with urticaria because they cause less sedation and have fewer anticholinergic effects (NICE).
- First‑generation agents cross the blood-brain barrier and can cause marked sedation and anticholinergic adverse effects.
- First‑generation agents should be used with caution in children and older adults.
- First‑generation agents remain useful as adjuncts when sedation is acceptable or desirable, for example for night‑time relief or refractory pruritus.
- Antihistamines relieve cutaneous histamine‑mediated symptoms but do not treat airway oedema or cardiovascular collapse.
- Antihistamines are adjunctive, not primary therapy, in anaphylaxis (Resuscitation Council UK).