Drug allergy labels and complications after surgery: a prospective multi-centre cohort study

Background One in four surgical patients carries a drug allergy label, of which an estimated 90% are incorrect. Avoidance of first-choice drug therapies may lead to worse postoperative outcomes. We sought to determine the nature and extent of any association between drug allergy labels and postoperative complications. Methods A multicentre observational study in 21 NHS hospitals. Eligible patients were 18 years or older, undergoing common surgical procedures: primary hip or knee replacement; internal fixation of closed long bone fracture; colorectal resection; trans-urethral resection of prostate or bladder tumour; caesarean section; hysterectomy. Exclusion criteria: use of antibiotics in the two weeks prior to surgery, previous participation in the study. Primary outcome was postoperative complications within 30 days following surgery, a composite outcome comprising: all postoperative infections, anastomotic leak, acute respiratory distress syndrome, myocardial infarction, postoperative bleed, pulmonary embolism, stroke, antimicrobial side effects, death. Results Among 13,646 patients, 3924 (29%) carried greater than or equal to1 drug allergy labels. Labelled patients were more likely to develop postoperative complications (989/3924 (25%) vs 1926/9722 (20%); OR 1.21 [1.10-1.34]; p<0.001). They were more likely to develop surgical site infections (337/3924 (9%) vs 760/9722 (8%); OR 1.19 [1.03 -1.38]; p<0.018), and any postoperative infection (750/3924 (19%) vs 1472/9722 (15%); OR 1.24 [1.11-1.38] p<0.001). Labelled patients experienced increased risk of allergic drug reactions (31/3924 (0.01%) vs 29/9722 (<0.01%); OR 3.00 [1.77-5.09]; p<0.001), but no increase in mortality. Conclusions Drug allergy labels are common, but often incorrect. Labelled patients experience worse postoperative outcomes, including infective and non-infective complications and increased risk of allergic drug reactions. Trial registration Registered with ISRCTN registry, ISRCTN15775657.