Patch Testing in Adverse Drug Reactions

A CADR is a skin eruption induced by drugs, systemic or topical drugs, used in adequate doses and in the correct indications. CADRs are a frequent problem in Dermatology, but their incidence is not exactly known; 1–5% of inpatients experience such a reaction and it is a frequent cause of consultation in Dermatology [1–5]. Most CADRs are mild, but about 20% can be severe and require hospitalization, for example, in patients with drug hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms (DRESS) and toxic epidermal necrolysis which, apart from the skin, have involvement of other organs [5]. Considering its pathomechanism, CADRs can be divided into several types. Most cases belong to type A and C, predictable and chemical, which represent an exaggerated pharmacologic activity of the drug, such as cheilitis from isotretinoin, or xerosis and papulo-pustulo-follicular reactions from inhibitors of epidermal growth factor receptor [6]. They can be enhanced by modification of drug bioavailability due to drug interactions, reduced metabolization, or elimination, especially in genetically susceptible individuals. Type D includes late (delayed) reactions, such as teratogenesis or carcinogenesis, and type E results from end-of-dose reactions [7]. Type B reactions are idiosyncratic, unexpected, unpredictable, and among these, many are due to immune reactions induced by the drug [5] (Table 26.1). Patch Testing in Adverse Drug Reactions