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Cutaneous reactions to drugs 

Cutaneous reactions to drugs

Cutaneous reactions to drugs

Peter S. Friedmann

, and Eugene Healy



Pathophysiology—discussion of HLA associations for generation of drug hypersensitivity reactions.

Clinical manifestations—new section on systemic hypersensitivity reactions: drug reaction with eosinophilia and systemic symptoms (DRESS).

Updated on 28 Nov 2013. The previous version of this content can be found here.
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date: 23 April 2017

Adverse drug reactions (ADR) are responsible for about 5% of all hospital admissions, and 10 to 20% of hospital inpatients develop ADRs, many of which involve the skin. ADRs are classified into five groups: (1) type A (augmented)—the most common form of drug reaction, and predictable from the normal pharmacological effects of the drug or its metablite; (2) type B (bizarre)—are not predictable and reflect patient individuality; most cutaneous drug reactions, including hypersensitivity reactions, are of this type; (3) type C (chemical)—can often be predicted from the structure of the drug or its metabolites; some cutaneous reactions are of this type; (4) type D (delayed)—e.g. teratogenicity; (5) type E (end of dose)—withdrawal reactions.

Drugs can induce a very wide variety of skin lesions, ranging from maculopapular eruption/toxic erythma (the most common drug-induced rash, often due to antibiotics) through to the spectrum of erythema multiforme (characterized by target lesions), Stevens–Johnson syndrome (when mucosal surfaces are affected), and toxic epidermal necrolysis (when the blisters become confluent and affect >30% of the skin).

The key to identifying which drug may be responsible for a suspected drug reaction is a thorough clinical assessment in the form of a careful drug history and precise description of the clinical features. Immune mediated reactions require previous exposure or at least a week of ongoing exposure to induce allergic sensitization. In vivo or in vitro tests are of limited use because, for most drugs, the antigenic molecule, hapten or metabolite is not known or available.

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