Drug Allergy

Abstract

Adverse drug reaction is a noxious and unintended response to a drug. Adverse drug reactions are separated into two major types: type A which is dose dependent and predictable and type B which is dose independent and usually unpredictable. The majority of adverse drug reactions are type A (e.g., bleeding secondary to warfarin). Type B reactions, which include hypersensitivity drug reaction, comprise of about 24 % of all adverse drug reactions. Drug allergy is considered a hypersensitivity reaction for which a definite immunologic mechanism, either IgE or T cell mediated, is demonstrated. An example is type I IgE-mediated allergic reaction to penicillin. True overall incidence of adverse drug reactions is unknown for the general population. The overall incidence of serious adverse drug reactions was 6.7 % of hospitalized patients and of fatal adverse drug reactions was 0.32 % of hospitalized patients. In 1994, fatal adverse drug reaction ranked the fifth leading cause of US deaths. In Singapore, a 2-year prospective study, using a network-based electronic notifications system for which each drug allergic case was verified by a trained allergist, detected the incidence of drug allergy was about 4.2 per 1000. Medication is the most common cause (58.8 %) of anaphylactic death in the USA from 1999 to 2010, and there was a significant increase in fatal drug-induced anaphylaxis from 0.27 per million in 1999–2001 to 0.51 per million in 2008–2010. Adverse drug reactions are encountered by physicians frequently. The reaction can be serious and fatal if not treated promptly and preventatively. Practitioners should be aware of therapeutic and preventive strategies for drug allergy.