Sex-based differences in penicillin allergy labeling among adults in a Canadian ambulatory urgent medicine clinic: a cross-sectional study

Abstract Background: Penicillin allergy labels (PALs) affect about 10% of people, are mostly low risk, and more common in females. Sex-based differences in prevalence and characteristics remain unclear. This study examined associations between sex, PAL, and relevant covariates, in an Ontario ambulatory hospital population. Methods: A cross-sectional study of adults ( ≥18 years) seen at the hospital’s Urgent Medicine Clinic from 2015–2024 was conducted. Descriptive statistics compared patients by PAL status. Unadjusted and multivariable logistic regression models evaluated associations between sex and PAL, adjusting for covariates. Results: Among 29,645 patients (59.7% female), 3,026 (10.2%) had a documented beta-lactam allergy, of which 2,777 (9.4%) were PALs, and most (91.7%) were low risk. Females were twice as likely to have a PAL (11.6% vs 6.0%; unadjusted OR 2.17, 95% CI 2.14–2.19) and more often reported multiple medication allergies (30% vs 16%; OR 2.25, P < .05). After adjusting for covariates, female sex (OR 1.47, 95% CI 1.34–1.62), atopic conditions (OR 1.46, 95% CI 1.29–1.66), age ( >80 years [vs <65 years]: OR 1.16, 95% CI 1.02–1.32), and number of other medication allergies (2: OR 10.44, 95% CI 9.28–11.74; ≥3: OR 13.33, 95% CI 11.72–15.16 vs 0 or 1) were associated with higher odds of PAL. Conclusion: Approximately 10% of patients had a PAL, mostly low risk and female predominant. Multivariable analysis identified female sex, atopy, older age, and multiple medication allergies as independent predictors; autoimmune and metabolic conditions were not. Longitudinal studies using validated allergy data and intersectionality can guide equitable evaluation.