Allergic Reaction & Anaphylaxis 🤧⚡️

📌 Overview

This topic covers the spectrum from mild allergic reactions to life-threatening anaphylaxis in adults.
Allergic reactions range from localised urticaria to systemic involvement with hypotension or airway compromise.
Management differs based on severity — assess airway, breathing, circulation and skin findings to triage appropriately.

IgE-mediated: prior sensitisation (e.g. peanuts, penicillin).
Complement-mediated: e.g. hereditary angioedema (C1 esterase inhibitor deficiency).
Anaphylactoid: first exposure (e.g. morphine, NAC); IgE not involved; same treatment.

Symptoms: localised urticaria, pruritus, mild swelling, no airway/breathing/circulation involvement.
Oral antihistamines: Cetirizine (non-sedating) 10mg PO once daily or Chlorphenamine (sedating) 4mg PO QID.
Steroids are generally not required.
Monitor for progression if recent exposure to allergen.
Patient can usually be discharged if symptoms resolve and no systemic features emerge.

Call for senior help immediately.
Remove trigger if known (e.g. stop infusion).
IM adrenaline 500 micrograms (0.5ml of 1:1000) to anterolateral thigh.
Use 25 mm needle for IM injection; use 38–40 mm if patient >100 kg to ensure intramuscular delivery.
Repeat every 5 minutes up to three times as needed.
No contraindication to IM adrenaline — give early if anaphylaxis suspected.
High-flow O₂, IV access, ECG, and obs.
Fluids: 500–1000ml crystalloid bolus if hypotensive. Don't sit patient up.
For cutaneous symptoms, non-sedating antihistamines (e.g. Cetirizine 10mg PO) can be given after adrenaline.
If patient is on beta-blockers and not responding to adrenaline, consider IV glucagon 2–3 µg/kg (max 1–2 mg).
Role of steroids is not proven.

Document allergen. Educate on avoidance.
Prescribe adrenaline auto-injector on discharge. Note: auto-injectors are for patient/community use and are not first-line in clinical emergencies.
Refer to GP/allergy clinic for long-term management.