# Temporal Trends in the Prescription of Biosimilars and the Status of Switching from Original Biologics to Biosimilars at Individual and Institutional Levels in Japan

## TL;DR

This study examines how biosimilars are prescribed in Japan over time and how often patients and institutions switch from original biologics to biosimilars.

## Contribution

The study provides new insights into biosimilar adoption trends and switching behaviors at both individual and institutional levels in Japan.

## Key findings

- Biosimilar prescriptions varied widely by drug, with 92.5% for filgrastim but only 13.6% for somatropin in May 2024.
- Only 1.2–14.0% of patients switched from original biologics to biosimilars, suggesting infrequent switching at the individual level.
- University-related hospitals were more likely to adopt biosimilars compared to clinics and other hospital types.

## Abstract

To describe the temporal trends in the prescription of biologics in Japan, with additional analysis focusing on switching from original biologics to biosimilars at the individual and institutional levels.

Using the JMDC claims database from January 2005 to May 2024, we identified patients who received at least one prescription for 17 biologics (original biologics or biosimilars). We elucidated the monthly trends in the proportions of original biologics and biosimilars. We also estimated the proportion of patients receiving original biologics only, those receiving biosimilars only, and those switching from original biologics to biosimilars (and vice versa) during the study period. Finally, we estimated the proportion of medical institutions that started prescribing biosimilars during the study period based on the type of medical institution.

Temporal trends in the proportions of original biologics and biosimilars varied widely. In May 2024, the proportion of biosimilar prescriptions was 13.6% for somatropin and 92.5% for filgrastim. At the individual level, the proportion of patients switching from original biologics to biosimilars was low (1.2–14.0%), indicating that switches do not often occur within the same patient, while more recent new users of biologics start biosimilars. At the institutional level, university-related hospitals and clinics were more and less likely, respectively to introduce biosimilars than public and other types of hospitals.

Temporal trends in the prescription of biosimilars and switching patterns varied widely by the type of biologics. The type of medical institution should be considered when assessing and promoting the use of biosimilars. Further research and strategies to increase the use of biosimilars in clinics may be needed.

The online version contains supplementary material available at 10.1007/s43441-025-00850-7.