Anaphylaxis may be defined as a severe, life-threatening, generalised or systemic hypersensitivity reaction.


  • Incidence: 20.00 cases per 100,000 person-years
  • Peak incidence: 20-30 years
  • Sex ratio: 1:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+


Common identified causes of anaphylaxis:
  • food (e.g. nuts) - the most common cause in children
  • drugs
  • venom (e.g. wasp sting)

Clinical features



Anaphylaxis is one of the few times when you would not have time to look up the dose of a medication. The Resuscitation Council guidelines on anaphylaxis have recently been updated.

Adrenaline is by far the most important drug in anaphylaxis and should be given as soon as possible.

The recommended doses for adrenaline, hydrocortisone and chlorphenamine are as follows:

< 6 months150 micrograms (0.15ml 1 in 1,000)25 mg250 micrograms/kg
6 months - 6 years150 micrograms (0.15ml 1 in 1,000)50 mg2.5 mg
6-12 years300 micrograms (0.3ml 1 in 1,000)100 mg5 mg
Adult and child > 12 years500 micrograms (0.5ml 1 in 1,000)200 mg10 mg

Adrenaline can be repeated every 5 minutes if necessary. The best site for IM injection is the anterolateral aspect of the middle third of the thigh.

Management following stabilisation:
  • patients who have had emergency treatment for anaphylaxis should be observed for 6–12 hours from the onset of symptoms, as it is known that biphasic reactions can occur in up to 20% of patients
  • sometimes it can be difficult to establish whether a patient had a true episode of anaphylaxis. Serum tryptase levels are sometimes taken in such patients as they remain elevated for up to 12 hours following an acute episode of anaphylaxis.