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# ICH Guide Seeks to Reduce Rat Studies
- URL: https://www.fdaweb.com/ich-guide-seeks-to-reduce-rat-studies/
- Published: 2021-05-14T12:00:00.000Z
- Updated: 2026-09-14T16:58:54.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5149330

The International Council for Harmonization is challenging the usefulness of two-year rat studies in a just-released *Addendum to the Guideline on Testing for Carcinogenicity of Pharmaceuticals S1B(R1)*. The [document](https://database.ich.org/sites/default/files/ICH%5FS1BR1%5FStep2%5FDraftGuideline%5F2021%5F0510.pdf?ref=fdaweb.com) expands the testing scheme for assessing human carcinogenic risk of small molecule pharmaceuticals by introducing an additional approach that is not described in the original S1B Guideline — a weight-of-evidence approach to determine whether or not a two-year rat study adds value in completing a human carcinogenicity risk assessment. “Application of this integrative approach would reduce the use of animals in accordance with the Rs (reduce/refine/replace) principles, and shift resources to focus onto generating more scientific mechanism-based carcinogenicity assessments, while promoting safe and ethical development of new small molecule pharmaceuticals,” the guide says.