4th July 2023

Causes

There are several causes of drug reactions including

1. Allergic reactions
   • Immediate reaction is mediated by IgE antibodies
   • Delayed reactions mediated by IgG antibodies, immune complexes and cytotoxic T cells
2. Pseudoallergic reactions
3. Dose-related reactions

A careful history and skin examination is required to diagnose the eruption. Blood tests, including full blood count (noting neutrophils and eosinophils), renal function and liver function, may also be useful.

Morbilliform drug eruption on back

Image Source: Wikimedia Commons (2013). Drug reaction, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Drugreaction.jpg (Accessed on: 1 April 2022).