Disproportionate drug allergy labelling among middle-aged patients and barriers to excipient allergy testing from the Hong Kong Comprehensive Excipient and Drug Allergy Registry (CEDAR)

Background: Longitudinal whole-population studies can explore new dimensions in drug allergy research. Excipient allergy testing remains a barrier to allergy evaluation in countries without legislations mandating ingredient disclosure in registered drugs. The Comprehensive Excipient and Drug Allergy Registry (CEDAR) was established to investigate Hong Kong’s drug allergy landscape and potential role of excipient registries. Methods: Drug allergy data from over 7,337,778 individuals between 2016-2021 was analyzed. Excipient lists were gathered from all formulations of the top 50 reported drug allergies and checked for the presence of polyethylene glycol (PEG). Results: The absolute-prevalence and -incidence of reported drug allergy was 5.61% and 277/100,000 population in 2021, respectively. Annual incidence of newly reported drug allergy was stable between 2016-2019, until a significant drop in 2020 (-16.3%, p=0.037). The most common implicated drugs were anti-infectives (245,832 [44.5%]), NSAIDs (106,843 [19.3%]), and nervous system drugs (45,802 [8.3%]). There was significant higher incidence among individuals aged >40, contributing to the majority of newly reported allergies (377,004, 68.2%). Beta-lactams and nervous system drugs were the most common reported culprits of anaphylaxis and Stevens-Johnson syndrome. CEDAR was unable to confirm presence or absence of PEG in any of the top reported culprits due to insufficient excipient information. Conclusion: We report the detailed drug allergy landscape of the Hong Kong population. Excipient registries are ineffective in countries without mandatory excipient listings . Contrary to traditional doagma, we identified a disproportionately higher incident drug allergy among middle-aged and older patients. Findings need to be confirmed by region-specific big data studies.