Cutaneous drug reactions: pathogenesis and clinical classification.

Cutaneous drug reactions may be classified with respect to pathogenesis and clinical morphology. They may be mediated by immunologic and nonimmunologic mechanisms. Immunologic reactions require host immune response and may result from IgE-dependent, immune complex-initiated, cytotoxic, or cellular immune mechanisms. Nonimmunologic reactions may result from nonimmunologic activation of effector pathways, overdosage, cumulative toxicity, side effects, ecologic disturbance, interactions between drugs, metabolic alterations, or exacerbation of preexisting dermatologic conditions. Certain defined, cutaneous, morphologic patterns are frequently associated with cutaneous drug reactions. These include urticaria, photosensitivity eruptions, erythema multiforme, disturbance of pigmentation, morbilliform reactions, fixed drug reactions, erythema nodosum, toxic epidermal necrolysis, lichenoid eruptions, and bullous reactions. In addition, certain drugs cause defined cutaneous syndromes. These include iodides and bromides, hydantoins, corticosteroids, antimalarial agents, gold, cancer chemotherapeutic agents, tetracyclines, thiazides and sulfonamides, nonsteroidal anti-inflammatory agents, and coumarin. The criteria for evaluation of possible drug reactions are presented and reviewed.