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Anaphylaxis

Emergencies

IM adrenaline is the first and most important treatment. If in doubt, give it.

Antihistamines and steroids are not part of the emergency treatment.

0:00

Start when the event began (or now)

  1. 0′

    Now

    • Call for help; remove the trigger; lie flat (sit up if breathing is easier).
    • IM adrenaline 500 micrograms (0.5 mL of 1 mg/mL) into the anterolateral thigh.
    • High-flow oxygen; IV access; monitoring.
  2. 5′

    No better at 5 minutes

    • Repeat IM adrenaline.
    • IV crystalloid bolus 500–1000 mL if circulation is a problem.
  3. 10′

    No better after two IM doses

    • Refractory anaphylaxis: critical care now.
    • Low-dose IV adrenaline infusion, run by a specialist; keep giving IM doses every 5 minutes until it starts.

Act now

  1. 1

    Call for help. Remove the trigger if possible (e.g. stop the infusion).

  2. 2

    Lie the patient flat (sit up if breathing is difficult); do not let them stand or walk.

  3. 3

    Give IM adrenaline into the anterolateral thigh. Repeat after 5 minutes if ABC problems persist.

  4. 4

    High-flow oxygen; IV fluid bolus if shocked or not responding to the first dose.

Assess

  • Sudden airway and/or breathing and/or circulation problems, usually with skin or mucosal changes, after a likely trigger.
  • Skin or mucosal changes alone are not anaphylaxis.

Investigations

  • Mast cell tryptase: first sample as soon as resuscitation is under way, second at 1–2 hours (no later than 4 hours).
  • Continuous monitoring: SpO₂, ECG, non-invasive BP.

Manage

  • Refractory anaphylaxis = ABC problems persisting after 2 appropriate IM doses. Needs an IV adrenaline infusion run by experienced clinicians (critical care).
  • Non-sedating oral antihistamine may be given after stabilisation for skin symptoms.
  • Before discharge: adrenaline auto-injectors with training, written action plan, allergy clinic referral. Report to the UK Anaphylaxis Registry if local process requires.

Escalate when

  • Immediately to critical care if no response after 2 IM doses, airway compromise or persistent shock.

Doses and prescribing

Adult and child over 12: adrenaline 500 micrograms IM = 0.5 mL of 1 in 1,000 (1 mg/mL). In hospital, draw up from an ampoule — most auto-injectors deliver less than 500 micrograms.

IV adrenaline boluses are for specialists only (e.g. anaesthesia, critical care).

Fluids: adult crystalloid bolus 500–1000 mL, reassess and repeat as needed.

Patients on beta-blockers may respond poorly — escalate early.

Check the BNF and your local formulary before prescribing.

Written to current guidance · sources checked 14 Nov 2026. We watch NICE for updates weekly.

Sources (2)

Reviewed by Aboodee Alhasso, MPharm MRCPharm IP on 14 Nov 2026

For healthcare professionals, as an aid to clinical judgement — not a substitute for it. Follow your local policy and ask a senior when in doubt.