Sci Rep. 2025 Aug 7;15(1):28853. doi: 10.1038/s41598-025-14816-0.ABSTRACTWe aimed to determine the use/prescription rates of biosimilars (BSs) among patients being treated with biologic or targeted synthetic disease-modifying antirheumatic drugs (b/tsDMARDs). This retrospective study included 647 patients with axial spondyloarthritis (axSpA) and rheumatoid arthritis (RA). Patients' manual and electronic file records were reviewed and demographic, clinical, laboratory, and treatment-related data were collected. Details of the last prescribed and previously used b/tsDMARDs were noted. The data obtained were compared between groups according to disease type or BSs use. Logistic regression analysis was used to identify potential predictors associated with prescribing BSs. The mean age of all the patients was 48.1 ± 12.6 years, and 66% of the patients were women. The rate of BS use was 21.2% in all patients, and there was no significant difference in the rate of BS use between the axSpA and RA groups (22.2% vs. 19%; p = 0.337). The total duration of all b/tsDMARDs use was 4.3 (1-8.3) years in all patients. Although there was no difference between the patients with axSpA and RA in terms of total treatment duration with the last b/tsDMARD (p = 0.655), the total duration of all b/tsDMARDs use was significantly higher in patients with RA than in patients with axSpA (p = 0.001). The use of BSs increased with the number of treatment switches and prescription order(s) of b/tsDMARDs. The BSs prescription rate (39.7%) was highest in drugs prescribed as fifth order or later in patients with prior use of five or more distinct b/tsDMARDs. Female sex, disease duration, and the order of current b/tsDMARD were the most important predictors of preference for BSs over reference drugs. Approximately one in five patients were prescribed BSs among the patients being treated with b/tsDMARDs. The use/prescription rates of BSs were independent of disease type. In patients receiving two or more different b/tsDMARDs, the prescription rates for BSs tended to rise with later treatment line(s) relative to first-line b/tsDMARDs.PMID:40770051 | DOI:10.1038/s41598-025-14816-0