chapter  9
Determining Allergic Versus Nonallergic Drug Reactions
ByGailen D. Marshall, Jr., and Phillip L. Lieberman
Pages 16

With the biochemical diversity and steadily increasing the number of commercially available pharmaceutical agents, the incidence of adverse drug reactions is also increasing. Even though allergists are most commonly consulted after a signi cant adverse drug reaction, due to type I [immunoglobulin (IgE)] hypersensitivity, other distinct immune reactions are possible (1). Additionally, many adverse drug reactions are nonimmunologic in origin. Such reactions may be categorized as predictable because they are dose-dependent, they derive from

they can occur in most people who take the drug. Predictable adverse drug reactions include toxic effects due to excess drug exposure (e.g., somnolence in opiate analgesics), drug interactions, or psychological effects prompted by anxiety over known or previously experienced side effects (such as mucosal irritation, gastrointestinal upset, skin rash, malaise, fatigue, etc.). Conversely, administration of a drug may produce unpredictable reactions, which are typically not dose-dependent and may be seen only in particularly susceptible patients. Unexpected adverse reactions may include idiosyncratic reactions or drug intolerance in which a standard dose produces extreme side effects not experienced at a reduced dose. Finally, initial immune-based drug reactions are unpredictable, but subsequent reactions may be predictable under appropriate conditions. Allergic and other immune-based drug reactions cause 6-10% of all observed adverse drug reactions, and the risk of an allergic reaction for most drugs is 1-3% (2).