In Japan, prescription drug labeling has transitioned to a new structured format aimed at improving clarity and consistency, with full implementation in March 2024. Abnormal kidney function, a critical determinant of drug safety, necessitates clear and consistent contraindication labeling. However, current labeling practices have not been comprehensively evaluated.

To systematically assess how kidney-related contraindications are described in Japanese package inserts under the new labeling format.

We reviewed all electronically available prescription drug package inserts as of October 1, 2024. Using 20 kidney-related keywords, we extracted and analyzed statements in Sect. 2 (“Contraindications”), categorizing them into four domains: type of impairment, severity, disease progression, and quantitative criteria. Additionally, a network diagram of co-occurring terms was developed to illustrate the consistency and diversity of terminology.

A total of 233 kidney-related contraindication statements were identified across 182 pharmaceutical ingredients. Type of impairment was mentioned in 81.5%, severity in 54.9%, and quantitative criteria in 38.2%. However, the terminology and threshold values used were inconsistent. Terms such as “severe abnormal kidney function” were used without standardized definitions, and quantitative parameters (e.g., creatinine clearance, estimated glomerular filtration rate) varied across products.

Despite regulatory efforts to enhance labeling structure, kidney-related contraindication descriptions in Japan remain variable and lack standardization. These inconsistencies may hinder safe prescribing practices and the integration of labeling into clinical decision support systems. Adoption of internationally harmonized terminology, such as KDIGO staging, and clearer regulatory guidance may improve the clinical utility of drug labeling.