Anaphylaxis

Global core

Anaphylaxis is a severe, fast allergic reaction with airway, breathing, or circulation involvement. The first drug is intramuscular adrenaline, also called epinephrine, into the mid-outer thigh. An antihistamine or a steroid does not replace it. Repeat if there is no improvement. The labeled dose differs by age and by country, so a dose is not given here as if it were universal.

What stays the same

• Airway, breathing, or shock after an allergen is anaphylaxis. A rash alone is not.
• The first drug is intramuscular, into the mid-outer thigh.
• An antihistamine or a steroid does not replace it.

1. Recognize. Rash, swelling, wheeze, or collapse minutes after a drug, food, or sting.
2. Reason. Airway noise and falling blood pressure define severity. A rash alone is not anaphylaxis.
3. Prioritize. The airway and the blood pressure, before a long allergy history.
4. Act safely. Intramuscular adrenaline/epinephrine, lie the patient flat if tolerated, oxygen, and a repeat dose if needed.

Local adaptation

• United Kingdom

  The BNF names the drug adrenaline. Intramuscular adrenaline is first-line. The adult dose listed is 500 micrograms (0.5 mL of 1 mg/mL), repeated after 5 minutes if there is no improvement.

  BNF / NICE. Medical emergencies in the community (2026). Accessed 2026-09-29.

• United States

  US practice parameters use the name epinephrine. The cited summary of the practice-parameter update recommends intramuscular epinephrine in the mid-outer thigh, 0.01 mg/kg of 1 mg/mL, up to 0.5 mg in adults, with no absolute contraindication.

  AAAAI/ACAAI practice parameter, summarized by Cleveland Clinic Consult QD. Anaphylaxis: Highlights from the Practice Parameter Update (2023). Accessed 2026-09-29.

Exam lens

The first drug, the route, and what not to do first.