Background The marketing approval of the etanercept biosimilar SB4 was based on phase III studies on patients with rheumatoid arthritis, but extended to all etanercept indications. Currently, no randomized controlled trials have compared etanercept originator (ETN) with SB4 in patients with spondyloarthritis (SpA). However, the uptake of etanercept biosimilars in the treatment of SpA has been exponential in the Nordic countries, with marked differences across the countries [1].

Objectives To compare the one-year treatment retention in bio-naïve patients with SpA treated with ETN versus SB4. Furthermore, to explore baseline characteristics in the two patient groups.

Methods Observational cohort study. Patients with SpA (ankylosing spondylitis (AS), non-radiographic axial SpA (nrax-SpA) or uSpA)), starting etanercept as their first ever TNFi Jan 2014 through Jun 2017 were identified in biologics registers in the five Nordic countries. Baseline characteristics were retrieved from each biological register and comorbidity data through linkage to national registers. The country-specific data were then pooled for further analysis. Comparisons of treatment retention between ETN and SB4 were assessed through survival probability curves and one-year retention rates.

Results In total, 1015 patients were included, whereof 49% started ETN and 51% SB4. Baseline characteristics were similar in the two patient groups (Table?1).

One-year survival probability curves were similar for ETN compared to SB4 (Figure 1), and the proportions of patients remaining on drug after one year were comparable: ETN 66% (95%CI: 61-70%) and SB4 73% (95%CI: 68-78%). Further confounder-adjusted analyses are planned and will be presented at the conference.

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Conclusion In this observational study of 1015 patients with SpA from five Nordic countries, biologics-naïve patients starting treatment with originator versus biosimilar etanercept had similar baseline characteristics and similar one-year treatment retention rates, suggesting similar effectiveness and tolerability of the two drugs.

Reference [1] Glintborg, et al. Biological treatment in ankylosing spondylitis in the Nordic countries during 2010-2016: a collaboration between five biological registries. Scand J Rheumatol. 2018;47:465-74.

Acknowledgement This study received funding from NordForsk and from FOREUM.

Disclosure of Interests Bente Glintborg Grant/research support from: Biogen, Pfizer, AbbVie, Ulf Lindström: None declared, Daniela Di Giuseppe: None declared, Johan Askling Grant/research support from: Karolinska Institutet (JA) has or has had research agreements with the following pharmaceutical companies, mainly in the context of the ATRIS national safety monitoring programme for rheumatology biologicals: Abbvie, BMS, MSD, Eli Lilly, Pfizer, Roche, Samsung Bioepis, and UCB., Consultant for: Karolinska Institutet has received remuneration for JA participating in ad boards arranged by Lilly, Novartis, and Pfizer., Dan Nordström Grant/research support from: MSD, Pfizer, Consultant for: AbbVie, BMS, MSD, Novartis, Roche, Pfizer, UCB, Speakers bureau: Novartis, UCB, Sella Aarrestad Provan Consultant for: Novartis, Speakers bureau: Lilly, Björn Gudbjornsson: None declared, Merete L. Hetland Grant/research support from: BMS, MSD, AbbVie, Roche, Novartis, Biogen, Pfizer, Consultant for: Eli Lilly, Speakers bureau: Orion Pharma, Biogen, Pfizer, CellTrion, Merck, Samsung Bioepis, Kalle Aaltonen: None declared, Arni Jon Geirsson: None declared, Niels Steen Krogh: None declared, Lennart T.H. Jacobsson Consultant for: LJ has received lecture and consulting fees from Pfizer, Abbvie, Novartis, Eli-Lily and Janssen