DermNet NZ


Fixed drug eruption

Fixed drug eruptions (FDEs) characteristically recur in the same site or sites each time a particular drug is taken; with each exposure however, the number of involved sites may increase.

Fixed drug eruption is a type of allergic reaction to a medicine. Usually just one drug is involved, although independent lesions (patches) from more than one drug have been described. Cross-sensitivity to related drugs may occur and there are occasional reports of recurrences at the same site induced by drugs that appear to be chemically unrelated. Sometimes the inducing drug may be re-administered without causing reappearance of the patch(es) and there may be a refractory period during which no reaction can occur after the occurrence of FDE.

How does FDE occur?

Clearly some sort of allergy is involved but exactly how an FDE arises and in particular why just certain areas of skin are affected, has not been worked out.

What does it look like?

Fresh lesions are well defined, round or oval patches of redness and swelling of the skin, sometimes surmounted by a blister. This then fades to a purplish or brown colour.

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Fixed drug eruption

The lesions usually develop within 30 minutes to 8 hours of taking the drug. They are sometimes solitary at first, but with repeated attacks new lesions may appear and existing ones may increase in size. Lesions are more common on the limbs than the trunk; the hands and feet, genitalia (glans penis) and perianal areas are favourite sites. Lesions may occur around the mouth or the eyes. The genitals or inside the mouth may be involved in association with skin lesions or on their own.

As healing occurs, crusting and scaling are followed by a persistent dusky brown colour at the site. This may fade, but often persists between attacks. Pigmentation tends to be more extensive and pronounced in people with brown skins. Pigmentation from FDE fades when the causative drug is avoided. Non-pigmenting fixed eruptions have been reported with pseudoephedrine and piroxicam.

Local or general symptoms accompanying an FDE are mild or absent.

Drugs involved

The number of drugs capable of causing fixed eruptions is large. Most are due to the following:

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Authors: DermNet Editorial Board
Department of Dermatology, Waikato Hospital.

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