How many patients are switching to biosimilars? – Healthcare Economist

This is a key question if biologic drug prices are going to fall in the long term. We can decompose this question into 3 subquestions:

• What proportion of patients who initiate therapy start with a biosimilar?
• What proportion of patients already using a biological product switch to a biosimilar?
• Do patient or physician factors drive biosimilar prescribing patterns?

an article of Roberts et al. (2024) aims to answer these questions using the drug infliximab as a case study. Infliximab is indicated for a variety of autoimmune diseases. (e.g., rheumatoid arthritis, Crohn’s disease, psoriatic arthritis).

Methods

The authors use data from the American College of Rheumatology’s Rheumatology Informatics System to determine its effectiveness (RAISE) record. RISE is drawn from electronic medical record data from more than 1,000 US rheumatologists. The authors run a multilevel logistic regression model grouping patients by practice to examine the proportion of biosimilar prescribing that depends on patient versus physician practice factors.

Results

• Initiation of biosimilars: The authors found that for patients who initiated therapy, 21.6% received an infliximab biosimilar between 2017 and 2022. However, while <10% of patients initiated a biosimilar in 2017, by 2022 37% of Medicare patients, 51% of commercially insured, and 55% of Medicaid patients initiated a biosimilar version of infliximab. Patients in the lowest socioeconomic level (measured by Area deprivation index) were more likely to initiate a biosimilar (RR = 1.29, 95% CI: 1.01–1.66).
• Switching biosimilars. Although there was an increasing trend to initiate more biosimilar treatments, switching from biologic to biosimilar was less common. “86.4% of users who received at least two doses of infliximab remained with the formulation they were initially prescribed.” The majority of switchers switched from biologic to biosimilar (11.5%), with 1% switching from biosimilar to biologic and <1% switching between biosimilar versions of infliximab.
• Impacts at the practice level. The author’s multilevel model revealed that 34% of the variation in change is explained by variation between practices (measured by the intraclass correlation coefficient [ICC]). “The median new beginnings in a biosimilar was 16% (IQR: 6%–27%) across all practices. Nineteen practices had >40% new starts with a biosimilar…The mean percentage of patients changed from biocreator to biosimilar was 11% (IQR = 5-20%), but 14 practices changed >40% of their patients.”

Overall, we see a trend toward increased prescribing of biosimilars, but there is still significant variability depending on patient socioeconomic status and insurance type, with large variability in the use of biosimilars in rheumatology practices.