Background
Population-based studies have demonstrated the potential of use of ‘big data’ in clinical and drug allergy research.1-4 The availability of longitudinal datasets can explore new dimensions of drug allergy research which would not have been possible with only traditional single-centre or cross-sectional studies. For example, we previously reported one of the largest drug allergy epidemiological studies by taking advantage of Hong Kong’s unified electronic healthcare record system with data from more than 95% (7.1 million) of the population.1 Based on population-wide data, we were able to accurately report the near-absolute prevalence and annual incidence of reported drug and beta-lactam allergies. However, at the time, we were only able to provide a condensed one-year snapshot on the landscape of drug/beta-lactam allergy and did not further analyse the granularity of individual patient data; such as specific-drug allergy culprits, individual patients’ age of reported drug allergy or duration of reported drug allergy. More detailed analyses are also important to identify country- or population-specific characteristics, which may vastly differ from Western cohorts, to further inform future drug allergy interventions and research.5,6
Another important limitation to drug allergy evaluation and research is the ability to accurately identify specific culprit allergens. For example, it is well established that up to 90% of all reported penicillin ‘allergy’ are incorrect after allergy evaluation, likely due to initial misdiagnoses or loss of sensitisation over time.7-10Alternatively, mislabelled drug allergy can also be due to the possibility of missing hidden allergens found within drugs or vaccines such as in the case of excipient allergies.11,12Although an uncommon cause of drug allergy, excipient allergy can almost never be excluded in countries lacking in pharmaceutical legislations to mandate complete ingredient disclosure in registered medications. This can and has led to cases of missed- and mis-diagnoses with potentially lethal consequences.13-15 The devastating impact of such failures in pharmaceutical legislations have been exemplified during global COVID-19 vaccination campaigns. Despite genuine vaccine or excipient allergy being exceedingly rare, the indirect consequences from the fear of potential excipient allergy and inability to identify potential excipients among culprit drug formulations greatly impeded vaccine uptake and fuelled vaccine hesistancy.16-18
To overcome these issues, the Comprehensive Excipient and Drug Allergy Registry (CEDAR) was established in Hong Kong – allowing the use of big data to investigate reported drug allergies in detail, and to help establish an excipient registry to facilitate comprehensive drug allergy evaluations. Utilising CEDAR, we investigated the 5-year trend of detailed drug allergy epidemiology and the potential role of an excipient registry to aid drug allergy evaluation. In particular, we selected polyethylene glycol (PEG), one of the most widely implicated excipients since the launch of mRNA COVID-19 vaccines, as an example for the potential use of excipient registries.