Fixed drug eruptions. Incidence, recognition, and avoidance.

Drug eruptions often have nonspecific clinical findings, and the evaluation of the probability of an eruption being a drug-induced event is difficult. A few types of drug eruption do not present such problems, and the fixed drug eruption is one of those whose clinical findings are specific enough to allow a diagnosis. The fixed drug eruption is a commonly reported type of drug eruption. The incidence of fixed drug eruptions has tended to increase, although the overall number of drug eruption cases has decreased. This is one of the reasons why fixed drug eruptions are familiar to dermatologists. The most characteristic findings of a fixed drug eruption are recurrence of similar lesions at the same sites and healing with residual hyperpigmentation. The residual hyperpigmentation serves as an indicator of site recognition. Diagnosis is not always easy; for example, as is the case for nonpigmenting fixed drug eruptions, which do not have any residual hyperpigmentation. The development of molecular biology may help to clarify the pathogenesis of fixed drug eruptions, but the reason for their recurrence on the same sites is still unknown. Identification of the causative drug or drugs is essential for the management of fixed drug eruptions, as it is for other drug eruptions. The causative drug or drugs and cross-reactants should be avoided to prevent recurrence. To date, rechallenge is the most reliable method of identifying causative drugs, but increasingly the use of skin tests has gained the attention of investigators. The validity and the problems of skin tests are discussed, and an approach to the clinical management of fixed drug eruptions is presented.