Aims: To estimate the cost impact of non-medical switching from originator to biosimilar etanercept in stable patients with rheumatoid arthritis (RA) in the UK. Materials and methods: A cohort-based decision tree model was developed with a 1-year time horizon. The model population included patients with stable RA (patients who responded to originator etanercept treatment with no treatment changes in the previous 6 months). Patients could undergo a non-medical switch to a biosimilar and then switch treatment again, if medically required, after 3-6 months. Data on the proportion of patients switching therapies, baseline healthcare resource use, and impact of switching on resource use were sourced from a survey of 150 rheumatologists from EU5 markets (France, Germany, Italy, Spain, UK). The average impact of switching was evaluated as mean values for change in resource utilization due to switching. Also, low- and high-impact scenarios (lower and upper values of the 95% confidence intervals for change in resource utilization due to switching) were modelled as sensitivity analyses. Cost data came from published UK sources. Results: The model assumed that 5,000 patients were treated with originator etanercept, with 1,259 (25.2%) switching to a biosimilar. Of those, 875 (69.5%) and 384 (30.5%) switched to SB4 and GP2015, respectively. After 3 months, 26.3% of patients who switched treatments did so again: 8.3% back to originator, 3.8% to the other biosimilar, and 14.2% to another biologic. Although originator etanercept was more expensive than the biosimilars, switching was more costly than continuous originator treatment across all impact scenarios. Switching treatment chains had higher overall annual per-patient costs than continuous originator treatment. Switching was associated with increased healthcare resource use. Limitations: Results from this analysis are not transferable to other (non-RA) etanercept indications. Conclusion: Non-medical switching can result in increased payer costs because of increased healthcare resource use following switching.

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