Drug-induced skin disease.

Drug-induced cutaneous reactions encompass a wide variety of rashes that depend in part on route of administration (e.g., contact versus systemic) as well as type of cutaneous response and molecular mechanism underlying the reaction. One such reaction is a type IV immunologic reaction (delayed hypersensitivity) manifest as contact dermatitis and commonly elicited by drugs such as antihistamines, antibiotic ointments, local anesthetics, and paraben esters in cosmetic creams and lotions. A generalized eruption of this sort will occasionally occur with systemic administration of a drug to someone previously sensitized by topical application. Systemic administration of agents can cause nonspecific pruritus or maculopapular eruptions that resemble visual exanthemas. The pathogenesis is unclear and no immune mechanism has been demonstrated. If the drug is continued, exfoliative dermatitis can result. Other types of reactions are urticarial in nature and include acute urticaria/angioedema, erythema multiforme (bullous and nonbullous), Stevens-Johnson syndrome, urticaria in association with serum sickness-like reactions, and urticaria associated with anaphylactoid reactions. In many of these, an allergic reaction in which there is an immunoglobulin (Ig) E-dependent release of mediators in the skin causes hives or swelling. In others, circulating immune complexes may be present, often involving IgG antibody complexed with drug and complement fixation; hives may then be caused by anaphylatoxin release or a concomitant IgE-mediated reaction. In some instances, a cellular reaction may augment the aforementioned inflammatory reactions, perhaps as part of a late-phase reaction or a true delayed hypersensitivity component.