Skin Disorders and Cutaneous Drug Reactions

The word dermatitis denotes an inflammatory erythematous rash. The disorders discussed in this chapter include contact dermatitis, seborrheic dermatitis, diaper dermatitis, and atopic dermatitis. Drug-induced skin disorders have been associated with most commonly used medications and may present as maculopapular eruptions, frxed-drug eruptions, and photosensitivity reactions. 

Diaper dermatitis (diaper rash) is an acute, inflammatory dermatitis of the buttocks, genitalia, and perineal region. The reaction is a type of contact dermatitis, as it results from direct fecal and moisture contact with the skin in an occlusive environment. 

Atopic dermatitis is an inflammatory condition with genetic, environmental, and immunologic mechanisms. Many immune cells have demonstrated abnormalities, including Langerhans cells, monocytes, macrophages, lymphocytes, mast cells, and keratinocytes. 

Drug-induced cutaneous reactions tend to be immunologic in origin and relate to hypersensitivity, but some reactions are nonallergic. The pathogenesis of fixed-drug reactions is not well understood. 

Drug-induced photosensitivity reactions are divided into phototoxicity (a nonimmunologic reaction) and photoallergic reactions (an immunologic reaction). The latter form is far less common. Medications associated with photosensitivity reactions include fluoroquinolones, nonsteroidal antiinflammatory drugs, phenothiazines, antihistamines, estrogens, progestins, sulfonamides, sulfonylureas, thiazide diuretics, and tricyclic antidepressants. 

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Skin Disorders and Cutaneous Drug Reactions CHAPTER 17... 

Mechanisms of non-immediate reactions are unclear but may be immunological and non-immunological. Delayed reactions of the IgE type are known (131). Aminopenicillins seem to be an important cause of non-immediate reactions (132-134). The morbilliform rash that begins 1-10 days after amoxicillin can be caused by a delayed cell-mediated immune reaction (135) as can fixed drug eruptions (136,137), toxic epidermal necrolysis (138-140), bullous erythroderma (141), and contact eczema (142). Investigation of these disorders should include delayed readings of skin tests (135). In patients with chronic urticaria, penicillin allergy was demonstrated by cutaneous tests. 

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