4th July 2023

Background

There are various types of cutaneous reactions to drugs which can range from mild to life threatening. One of the most common types is morbilliform or maculopapular drug eruption. The rash usually appears 1 to 2 weeks after starting the drug, such as antibiotics. It usually initially appears on the trunk then spreads to the neck and limbs symmetrically. Serum sickness occurs when the body produces antibodies to foreign proteins, often from non-human antitoxins or antivenoms. Fixed drug eruption occurs as a recurrent lesion at the same site after re-exposure to the causative drug.

On the more severe end of the spectrum, Severe Cutaneous Adverse Reactions (SCAR) include a number of conditions which are important to be aware of. These include Stevens-Johnson syndrome /Toxic Epidermal Necrolysis (SJS/TEN), Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) and acute generalised exanthematous pustulosis (AGEP).

SJS/TEN is a rare but serious condition that can be caused by several drugs such as antibiotics, e.g. cotrimoxazole, penicillin, anticonvulsants (such as carbamazepine and phenytoin), and allopurinol. In SJS/TEN, patients usually develop prodromal flu-like illness for several days before the rapid development of a painful blistering rash. It is known as SJS when <10% of skin is involved, SJS/TEN overlap when 10-30% of skin is involved, and TEN when >30% of skin is affected.

DRESS is also called drug induced hypersensitivity syndrome (DIHS). Symptoms may start 2-6 weeks after drug exposure. It usually affects several organs and is associated with swollen lymph nodes, eosinophilia, thrombocytopenia and abnormal liver function tests.

In AGEP, the rash appears around 2 days after starting the medication. It usually develops on the face and becomes widespread with pustules. It is associated with neutrophilia and raised inflammatory markers.