[Skin and hair].

Data deriving from comprehensive hospital monitoring systems suggest that drug-induced skin effects occur in 2-5% of patients receiving any drug medication. Exanthematous (maculopapular) reaction (75%) and urticaria with/without angioedema (30%) are the most frequent of all cutaneous reactions to drugs. The incidence of cutaneous reactions relates to the quantity of the drugs which is prescribed and consumed worldwide. Thus penicillin, sulfonamides and nonsteroidal antiinflammatory drugs show the highest rate of cutaneous side effects. Drug reactions may be classified as either predictable (e.g. chemotherapy-induced alopecia) or unpredictable. Unpredictable side effects of drugs may be the result of allergic (type I to IV) or non-allergic reactions. Hereditary and acquired enzyme deficiency and variations in metabolic pathway may delay drug metabolism and cause nonallergic, toxic side effects. Such a mechanism is known to occur in patients with a low acetylation rate under hydralazine, INH or sulfonamide treatment. Some immunologic although nonallergic factors may facilitate eruptions in patients with infectious mononucleosis under ampicillin medication and in AIDS patients on co-trimoxazole therapy. When a cutaneous drug reaction is diagnosed, withdrawal of the drug is recommended. In instances in which patients display mild drug eruptions and no alternative therapy is available, the drug may be continued. However, it should be kept in mind that mild morbiliform eruption is often the initial presentation of toxic epidermal necrolysis. In AIDS patients sulfonamides most frequently have been implicated as a risk factor for the development of toxic epidermal necrolysis. In other than type 1 hypersensitivity reactions, skin testing and in vitro tests have low sensitivity and specificity.