ABSTRACT

Adverse drug reactions involving the skin are a common problem but their real incidence is not known. Among inpatients 2-5% experience a cutaneous adverse drug reaction (CADR),1,2 but although it is a frequent cause of consultation or urgent observation at a Dermatology department,3 no precise data exist concerning its incidence in outpatients. Only 2% are severe reactions,1 therefore most are not reported to the pharmacovigilance systems. Also, in some cases, the diagnosis of CADR is one of presumption, with no defi nitive test to prove it, or of exclusion for which the dermatologist has to be alert. Some CADR are mild and resolve spontaneously, others represent an exaggeration of the drug pharmacological effect, some are similar to viral exanthems or idiopatic urticaria, and others mimic skin diseases which are not usually drug-induced, namely pemphigus, bullous pemphigoid, lupus erythematosus, psoriasis, and lichen plannus.1,3,4

Most CADR are certainly not immune mediated, representing a pharmacological drug effect often exaggerated due to drug interactions, concomitant diseases that modify drug

bioavailability, or predisposing genetic polymorphisms of drug detoxifying enzymes. As an example, skin and oral mucosa erosions can occur during metothrexate treatment in patients with low serum albumin, low renal clearance, or on concomitant use of nonsteroidal antiinfl ammatory drugs (NSAID). These predictable reactions, called type A, may represent up to 80% of CADR4 and are not the object of this chapter.