Patient out-of-pocket costs and rheumatology biosimilar competition

Despite demonstrated savings from biosimilars, evidence examining savings experienced by patients is mixed, especially in the commercially insured population. Reference product prices typically decrease after biosimilars enter the market, so documented savings from existing studies cannot causally conclude that biosimilar competition itself has led to overall patient out-of-pocket (OOP) savings for both reference products and biosimilars as prices come down.

To assess the impact of biosimilar competition on patient OOP costs for rheumatology biologics.

We used claims from the Merative MarketScan Commercial Database from January 1, 2011, through December 31, 2023, to conduct a Callaway and Sant'Anna difference-in-differences analysis of patient OOP costs before and after biosimilar competition. Patients were included if they had at least 2 drug claims for a single qualifying drug in each year of inclusion and had continuous enrollment for the whole year. We included infliximab, rituximab, and adalimumab as the drug groups of interest, as they are rheumatology biologics with biosimilars available. The control group consisted of drugs with similar mechanisms of action and place in therapy based on US Food and Drug Administration-approved indications and clinical guidelines to the drugs of interest that did not have biosimilars available during the study period. The exposure in the analysis was biosimilar competition (availability of biosimilars), and the outcome was biologic-related OOP costs.

We observed significant patient OOP savings because of biosimilar competition, with an average annual OOP difference of -$1,133.90 (95% CI -$1,200.35 to -$1,067.45) in the infliximab group, -$1,437.63 (95% CI -$1,549.98 to -$1,325.28) in the rituximab group, and -$375.01 (95% CI -$539.57 to -$210.45) in the adalimumab group compared with the control group during the study period (January 1, 2011, through December 31, 2023). In the adalimumab group, there were no patient savings in a scenario analysis that omitted the year before biosimilar entry to account for anticipatory price increases, and the results in that group are preliminary because there was only 1 year of data in the postperiod. When assessing treatment effect by duration of exposure, we observed increasing savings over time the longer biosimilars were available for infliximab and rituximab.

Biosimilar competition resulted in decreased OOP costs in patients using infliximab and rituximab biologics, using similar biologics without biosimilars available as a control group. Preliminary results for adalimumab are inconclusive. The results indicate that the availability of infliximab and rituximab biosimilars has led to significant savings for patients, with savings increasing the longer biosimilars remain on the market. Because of these demonstrated savings, it is important that policies incentivize development of biosimilars and support the long-term availability of biosimilars to preserve and increase savings for patients.