Supplementary Material for: Antibiotic Prescribing Practices Differ between Patients with Penicillin Intolerance and Penicillin Allergy Labels

Introduction: Penicillin allergy labels are common. However, many penicillin allergy labels have been applied incorrectly and in fact represent penicillin intolerance. Patients with penicillin intolerance can receive penicillin antibiotics. The effect of penicillin intolerance labels on prescribing practices is uncertain. Methods: This multicenter retrospective cohort study included consecutive general medicine patients admitted to two tertiary hospitals over a 12-month period. Electronic medical records were reviewed for allergy and prescribing practices. Instances of penicillin prescription to patients with previously labeled penicillin allergies underwent case note review. Results: There were 12,134 individual hospital admissions included in the study. The number of admissions with a previous penicillin allergy label was 1,312 (10.8%) and with a penicillin intolerance label was 60 (0.5%). Penicillin allergy labels were associated with increased likelihood of being prescribed vancomycin (odds ratio 1.42, 95% confidence interval 1.16–1.75, p = 0.001) and moxifloxacin (odds ratio 20.0, 95% confidence interval 13.4–29.9, p < 0.001). Penicillin intolerance was not associated with increased likelihood of receiving these antibiotics. There were 75 admissions during which an individual with a penicillin allergy label was prescribed one of the specified penicillins and only one adverse reaction in this group. These cases included eight deliberate challenges and 15 cases in which allergy history clarification was sufficient to delabel the allergy. Conclusions: This study supports that prescribing practices differ between patients with penicillin allergy labels and intolerance labels. Penicillin challenges may be undertaken safely in the inpatient setting. Further studies are required to investigate how best to interrogate penicillin allergy labels in this cohort.