Implementation of reduction and refinement-related parameters in repeated dose toxicity studies

Area of Science:

• Toxicology
• Chemical Safety Assessment
• Regulatory Science

Background:

• The Organisation for Economic Co-operation and Development (OECD) Test Guideline (TG) programme establishes standardized methods for chemical safety testing.
• These guidelines aim to harmonize testing and support the replacement, reduction, and refinement (3Rs) of animal use in regulatory testing.
• TG 407 (28-day repeated dose toxicity study) and TG 408 (90-day repeated dose toxicity study) are key guidelines for chemical safety assessment.

Purpose of the Study:

• To assess the implementation of reduction and refinement strategies within the OECD Test Guidelines 407 and 408.
• To evaluate the adherence to specific parameters related to animal use and testing design in repeated dose toxicity studies.
• To identify opportunities for enhancing the 3Rs principles within current OECD guidelines.

Main Methods:

• A review of 300 reports from repeated dose toxicity studies using rats (conducted for chemical safety purposes) was performed.
• The uptake of reduction- and refinement-related parameters in OECD TGs 407 and 408 was analyzed.
• Adherence to specific parameters such as group size, number of dose groups, maximum dose level, dose volume, limit tests, housing, and study duration was evaluated.

Main Results:

• Strong adherence was observed for minimum group size, number of dose groups, maximum dose level, and dose volume.
• However, the uptake of the limit test as a reduction method was very low in both TG 407 and TG 408.
• Evidence suggests continued use of individual housing and larger than minimum group sizes in TG 407 studies.

Conclusions:

• Current application of OECD TGs 407 and 408 shows high compliance with certain parameters but limited adoption of key reduction and refinement strategies.
• Opportunities exist to improve the guidelines to better align with the 3Rs principles.
• A systematic review by the OECD Test Guideline programme is recommended to ensure guidelines effectively support animal testing alternatives.