Drug allergies in the surgical population

Many patients claim to have drug allergies. However, the signs and symptoms of “allergic reactions” are seldom documented and the drug allergies are rarely properly assessed. The goal of this study was to determine the incidence of claimed “drug allergies” in a surgical population. After obtaining institutional approval, the study was carried out at five hospitals affiliated with Dalhousie University. Patients were interviewed by the investigators during the preoperative anaesthetic evaluation over six months and all signs and symptoms of drug reactions were recorded. The validity of the claimed allergy was based on the history. The allergies were assigned to one of three groups: (1) High probability of an allergic reaction: one or more of the signs and symptoms typical of an immunological reaction, with or without a family history, or a history of atopy: (ii) Low probability of an allergic reaction: signs and symptoms of the reaction were predictable reactions or side effects of the drug, without the occurrence of reactions mentioned above; or (iii) Unknown status. no information concerning the reaction of history was available. Of 1818 adult and paediatric patients (914 female/904 male) interviewed, 511 (28.1%) claimed to have one or more drug allergies (a total of 671 allergies). More women than men claimed to have drug allergies (60.3% vs 39.7%) and there was a positive correlation between age, number of medications and reported drug allergies. Antibiotics (50%), opioids (27%), nonsteroidal antiinflammatory agents (10%), and sedatives (5%) accounted for 92% of all claimed drug allergies. Overall, 50% of claimed allergies had a high probability of true allergic reactions. The majority of antibiotics (75%) were associated with a high probability for true allergic reactions, but most of the other drug classes, such as opioids (83%), NSAIDs (64%) and sedatives (67%), were associated with a low probability for true allergic reactions. Our findings suggest a serious problem in the “labelling” of our patients as having drug allergies. Patients and health care personnel should be educated in the differentiation between predictable adverse drug reactions and true allergic drug reactions.