16th February 2025

Overview of anaphylaxis

Anaphylaxis is a severe type I (IgE-mediated) hypersensitivity reaction. Excessive release of histamine from mast cells and basophils results in the following features:

• Angioedema – non-pitting swelling of deep tissues such as eyelids, lips, tongue and airway
• Skin changes – urticarial rash, flushing (absent in 20% of cases)
• Respiratory – bronchospasm, stridor
• Cardiovascular – distributive shock

The patient may also have reduced consciousness and arrhythmias, including supraventricular tachycardia.

The commonest medications to cause anaphylaxis are: antibiotics (particularly penicillins and cephalosporins), chemotherapy agents, contrast media, NSAIDs and neuromuscular blocking agents.