Anaphylaxis is a severe, life-threatening allergic reaction that develops quickly. The first and most important treatment is intramuscular adrenaline (epinephrine). Antihistamines and steroids do not treat the life-threatening features and must never delay adrenaline.
How to recognise anaphylaxis
Think anaphylaxis when there is a sudden onset of:
- Airway problems: swelling of the throat or tongue, hoarse voice, stridor
- Breathing problems: breathlessness, wheeze, falling saturations
- Circulation problems: pale and clammy, low blood pressure, faintness, collapse
Skin and mucosal changes such as hives, flushing or swelling are common, but they are absent in some cases, so do not rely on them.
Immediate actions
- Call for help and remove the trigger if possible (stop the infusion or transfusion).
- Position the patient: lie flat with legs raised if hypotensive; sit up if breathing is the main problem. Do not let the patient stand or walk. In pregnancy, use the left lateral position.
- Give IM adrenaline into the anterolateral thigh (doses below).
- Give high-flow oxygen and attach monitoring.
- Repeat IM adrenaline after 5 minutes if there is no improvement.
- Give an IV fluid bolus if there are circulation problems, as prescribed.
IM adrenaline doses (1 mg/mL, also written 1:1000)
| Age | Dose | Volume |
|---|---|---|
| Adults and children over 12 years | 500 micrograms | 0.5 mL |
| Children 6–12 years | 300 micrograms | 0.3 mL |
| Children 6 months to 6 years | 150 micrograms | 0.15 mL |
| Infants under 6 months | 100–150 micrograms | 0.1–0.15 mL |
Adult auto-injectors usually deliver 300 or 500 micrograms. If an auto-injector is all that is available, use it.
If the patient does not improve
Refractory anaphylaxis means breathing or circulation problems persist despite two doses of IM adrenaline. Get urgent expert help from the critical care or resuscitation team, who may start a low-dose IV adrenaline infusion. If the patient arrests, start CPR and follow advanced life support. IV adrenaline boluses should only be given by experienced specialists.
After the emergency
- Take mast cell tryptase samples if your protocol includes them: as soon as possible after starting treatment, again at 1–2 hours, and a baseline sample later.
- Observe for a biphasic reaction, in which symptoms return hours later. The length of observation depends on the severity and response to treatment.
- Record the suspected trigger clearly, update the allergy record and report drug reactions through your national system.
- Before discharge, make sure the patient has been prescribed and taught to use two adrenaline auto-injectors, knows to carry both at all times, and has been referred to an allergy clinic.
Related: High-alert medications list · Which antihistamine is best?
Sources: Resuscitation Council UK, Emergency treatment of anaphylaxis: guidelines for healthcare providers (2021); World Allergy Organization anaphylaxis guidance. Doses are for reference; always follow your local protocol.
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