Changes in drug price reduction trends during Japan's transition to an annualized revision environment: a comparative analysis using open data from the national claims database.

OBJECTIVE

To address the lack of evidence on the effects of Japan's transition to an annualized revision environment, this study quantified the net change in drug price reduction rates between the biennial and annualized revision periods, encompassing the introduction of off-year revisions and policy measures, and examined structural heterogeneity across drug types, dosage forms, and therapeutic categories.

METHODS

Longitudinal analysis was conducted using the National Database of Health Insurance Claims and Specific Health Checkups (NDB) Open Data. The study period was divided into Pre-period (2016-2019) and Post-period (2020-2023). Linear mixed-effects models (LMMs) were employed to estimate price change rates, adjusting for drug type, dosage form, therapeutic sub-categories, and log-transformed baseline price and prescription volume, with unique drug identifiers included as a random intercept.

RESULTS

The analysis included 4,448 drugs from 85 therapeutic sub-categories. Overall, the mean drug price reduction rate significantly accelerated in the Post-period, declining by an additional 4.46 percentage points (pp) compared with the Pre-period (p < 0.001). After covariate adjustment, the primary LMM estimate indicated a net acceleration of -6.65 pp (95% CI: -7.24 to -6.06; p < 0.001). The model also revealed pronounced bipolarization: oral drugs showed substantial acceleration in price reduction, with least squares (LS) means decreasing from -6.5% to -17.0% for brand-name drugs and from -15.6% to -27.3% for generics (p < 0.001 for both). Injection products showed divergent trajectories in the primary analysis. Severe price erosion occurred in antitumor agents (-13.3 pp), whereas high price resilience persisted in categories such as anticoagulants and hemodialysis solutions.

CONCLUSIONS

Japan's annualized revision environment (2020-2023) was associated with an acceleration in pharmaceutical cost containment, but also with bipolarization across product segments. Marked price erosion in oral drugs, together with pronounced therapeutic heterogeneity, suggests that uniform reductions should be reconsidered to safeguard access and continuity of care.