Drug Allergies

Abstract

Adverse drug reactions (ADRs) are an important public health problem. An ADR is defined by the World Health Organization as an unintended, noxious response to a drug that occurs at a dose usually tolerated by normal subjects. The classification of ADRs by Rawlins and Thompson divides ADRs into two major subtypes: (1) type A reactions, which are dose dependent and predictable, and (2) type B reactions, which are uncommon and unpredictable. The majority of ADRs are type A reactions, which include four subtypes: overdosage or toxicity, side effects, secondary effects, and interactions. Type B reactions constitute approximately 10 to 15% of all ADRs and include four subtypes: drug intolerance, idiosyncratic reactions, pseudoallergic reactions, and drug hypersensitivity reactions. This chapter reviews the epidemiology of ADRs, risk factors for drug hypersensitivity reactions, the classification of drug reactions, diagnostic tests, reactions to specific drugs, and management of the patient with drug allergy. Figures illustrate drugs as haptens and prohaptens, the Gell and Coombs system, the four basic immunologic mechanisms for drug reactions, the chemical structure of different β-lactam antibiotics, penicillin skin testing, sulfonamide metabolism and haptenation, nonsteroidal antiinflammatory drug effects, and patient management. Tables outline the classification of ADRs, drugs frequently implicated in allergic drug reactions, and reagents and concentrations recommended for prick and intradermal skin testing. This review contains 8 figures, 7 tables, and 60 references. Key Words: Adverse drug reactions, drug hypersensitivity reactions, overdosage, toxicity, Type A reactions, Type B reactions, human leukocyte antigen, pruritus, angioedema, urticarial, bronchospasm, laryngeal edema, rhinoconjunctivitis