The mechanism of these systemic reactions is not clear. In order to modify the course of this cutaneous eruption, suppression of delayed type hypersensitivity is needed and must be continued for a period of at least two weeks. Topical versus systemic glucocorticoid therapy may be chosen depending on the distribution and severity of the rash. The macule is pruritic and will evolve into a raised plaque or even a blister. Plaques are usually 2 to 4 cm in diameter.
Skin biopsy is helpful in making the diagnosis.
Lesions occur in descending order of frequency on the oral or genital mucosa, the face, and the extremities. After withdrawal of the drug, the lesion resolves leaving a hyperpigmented area of skin. If the drug is reintroduced the fixed drug eruption will recur at the same location. The mechanism of fixed drug eruption is not known. Topical corticosteroids may render the eruption somewhat less intense and speed resolution after discontinuation of the initiating drug.