This study investigated whether systemic drug prescribing for psoriasis varies by season and other exacerbating factors. Eligible patients with psoriasis were assessed for each season for initiation, discontinuation, and switching of systemic drugs. A total of 360,787 patients were at risk of initiating any systemic drugs in 2016‒2019; 39,572 patients and 35,388 patients were at risk of drug discontinuation or switching to a biologic and a nonbiologic systemic drug, respectively. The initiation of biologic therapy in 2016‒2019 peaked in spring (1.28%), followed by summer (1.11%), fall (1.08%), and winter (1.01%). Nonbiologic systemic drugs followed a similar pattern. Those aged 30‒39 years, male, those with psoriatic arthritis, those who live in the South region, those who live in areas with lower altitudes, and those who live in areas with lower humidity had higher initiation with the same seasonality pattern. Discontinuation of biologic drugs peaked in summer, and switching of biologics was highest in spring. Season is associated with initiation, discontinuation, and switching, although seasonality pattern is less clear for nonbiologic systemic drugs. Approximately 14,280 more patients with psoriasis in the United States are estimated to initiate a biologic in spring than in other seasons, and over 840 more biologic users switched in spring than in winter. The findings may provide evidence for healthcare resource planning in psoriasis management.
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