Brand-to-brand nonmedical switching among interleukin-17 inhibitors or other biologics: Implications of a formulary change

In 2021, a large pharmacy benefit management organization (PBM) changed preferred agents on its national formulary from one branded interleukin (IL)-17 inhibitor (TxA) to another (TxB), prompting a nonmedical switch (NMS) for patients using TxA. To evaluate the impact of this formulary change on treatment patterns among patients with psoriasis, psoriatic arthritis, or ankylosing spondylitis. Patients receiving TxA for at least 84 days and no other biologic from July 2020 to December 2020 were identified using PBM-specific data from the Symphony Health Analytics database. Two comparator groups were established: patients affected (PBM-1) and not affected (PBM-2) by the formulary change. Outcomes were (1) changes in monthly fills of TxA/TxB (July 2020 to June 2021; PBM-1 group only), (2) proportion of TxA-treated patients experiencing any medication discontinuation or switching (PBM-1 and PBM-2 groups), and (3) medication-taking behaviors (adherence, discontinuation, switching) among patients continuing TxA vs those that NMS to TxB (PBM-1 group only). Demographics were similar for patients in PBM-1 (N = 1,703) and PBM-2 (N = 462). After the formulary change (January 2021 to June 2021), TxA prescription fills decreased 7% while TxB fills increased 8% in the PBM-1 group. Compared with patients not affected by the formulary change (PBM-2 group), significantly more patients in the PBM-1 group completely discontinued treatment (27% vs 14%). The PBM-1 vs PBM-2 group had significantly higher (P < 0.001) rates of switching to TxB (19% vs 1%) or another biologic (8% vs 2%). Following NMS from TxA to TxB, patients in the PBM-1 group had significantly (P < 0.05) lower adherence rates (46% vs 63%) and higher rates of subsequent switching (14% vs 6%) or absolute discontinuation (20% vs 14%) than those continuing TxA. Following the formulary change, more than 25% of patients exposed to the change experienced treatment discontinuation, nearly double the rate than those not exposed. This unfavorable finding, along with higher rates of nonadherence and subsequent switching, warrants careful monitoring of similar policy changes.