Objective CVS Caremark changed their national commercial formularies in 2024 to prefer adalimumab‐adaz over originator. We assessed the formulary change's effect on biosimilar adalimumab prescribing in U.S. community rheumatology practices. Methods Data come from RISE, a registry of EHR data from participating community rheumatology practices nationwide. We used interrupted time series to analyze the effect of the CVS formulary change on the proportion of patients prescribed adalimumab‐adaz or other adalimumab biosimilars each month between January 2023 and September 2024 stratified by payor and among new users. Results We included 22,079 patients. Among commercially insured, prescriptions for ‐adaz went from nearly 0% to more than 25% following the CVS formulary change. In the next month, prescriptions for ‐adaz dropped 12.3%. Prescriptions for other biosimilars increased slowly and linearly over the study period. Among patients with Medicare, we observed a similarly timed, but much smaller, increase in prescribing for both ‐adaz and other biosimilar molecules without a large subsequent decrease. Among new users, prescriptions for ‐adaz increased from 0% to 24% but was followed by a nearly 14% decrease in prescriptions in the first month after the formulary change. Other biosimilar prescriptions increased 0.6% per month throughout the period. Conclusions While biosimilar adalimumab prescriptions rose sharply after a major national formulary change, the increase was not sustained. These findings highlight that persistent barriers, including the nocebo effect and the administrative burden of switching, may continue to limit biosimilar adoption and contribute to the loss of substantial cost savings in the US market.
Roberts et al. (Mon,) studied this question.