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Systemic therapies for psoriasis and psoriatic arthritis (PsA) have the potential to cause serious adverse events (SAEs), particularly among older adults (Garcia-Doval et al, 2012; Lavan and Gallagher, 2016). A network meta-analysis of clinical trials comparing the risk of SAEs with different systemic therapies for psoriasis did not find meaningful differences between medication classes (Sbidian et al, 2025). That analysis was mostly limited to short-term trials with low SAE rates, and clinical trials for psoriasis largely exclude older adults and include a low proportion of people with PsA (Sbidian et al, 2025; Schaap et al, 2020). Data are lacking on the relative rates (RRs) of overall SAEs among older adults with psoriatic disease.

The objective of this study was to estimate the association of different systemic treatment classes for psoriasis and PsA and the rate of all-cause SAEs among older adults. We hypothesized that biologics would be associated with relatively low rates of SAEs.

We utilized a previously described population-based cohort of new users of systemic therapy for psoriasis and PsA in Ontario; characteristics of the population at index were published previously (Drucker et al, 2025). Population-based datasets were linked using unique encoded identifiers and analyzed at ICES (Supplementary Materials and Methods). The use of data in this study is authorized under section 45 of Ontario’s Personal Health Information Protection Act and approved by the ICES Privacy and Legal Office, so it did not require review by a research ethics board or individual participant consent.

We included people with psoriasis or PsA, defined using a validated administrative algorithm (Eder et al, 2019), who were aged ≥66 years and dispensed their first systemic medication between April 2002 and December 2020. Medication exposure, derived from the Ontario Drug Benefit database, was classified into 6 categories: methotrexate, other older systemic medications, anti-TNF biologics, anti–IL-12 and -23 biologics, anti–IL-17 biologics, and tofacitinib. We combined biologics into those categories, despite some differences in individual mechanisms, because they target shared pathways. Apremilast was not assessed because it is not covered under Ontario Drug Benefit. Each medication class was operationalized as its own time-varying variable. Person-time accrued starting from their index medication dispensation until their death or end of follow-up (March 31, 2021). People in the cohort contributed person-time on and off the different medication classes as time progressed. For oral medications, we considered a medication to be discontinued if no subsequent dispensation was observed within 1.5 times the days supplied on their last prescription. For subcutaneous medications, we considered a medication discontinued at 1.5 times the number of units dispensed of a standard dose multiplied by the typical maintenance dosing interval (Supplementary Materials and Methods). For infliximab, we defined discontinuation as the longest of either 1.5 times the days’ supply or 1.5 times the standard dosing interval (8 weeks).

The main outcome was SAEs, defined as a composite of all-cause emergency department (ED) visits and hospitalizations, a proxy for all-cause SAEs as reported in clinical trials. ED visits were identified using the Canadian Institute for Health Information National Ambulatory Care Reporting System, and hospitalizations were identified using the Canadian Institute for Health Information Discharge Abstract Database.