Alternative methods for developmental toxicity testing: features, status and future directions

The developmental stage begins with implantation of a fertilized egg, followed by continuous cell division and differentiation to produce a complete organism. Developmental toxicity involves adverse effects that may be irreversible or undetectable until significant damage occurs, especially during early development, and must be assessed for drug and chemical safety. Animal tests face limitations such as cost, ethics, and species differences, prompting demand for alternatives. This review examines current alternative methods, institutional efforts, and future directions.

Recent advances have led to the use of various new approach methodologies to replace or complement animal testing. The embryoid body test now allows for faster and more reproducible assessment of early developmental toxicity, while organoids are being applied to evaluate organ-specific toxicities, such as neurodevelopmental and cardiac effects. Zebrafish offer validated endpoints for morphological and behavioral evaluation, enhancing their regulatory relevance. Predictive models, including those based on machine learning, are being integrated with in vitro data to strengthen mechanism-based analysis. These observations reflect a shift toward more human-relevant and efficient approaches in toxicity testing, which aligns with the central focus of this review. Regulatory bodies such as the Organisation for Economic Co-operation and Development are also actively promoting the acceptance and implementation of these methods.

Alternative methods provide ethical and rational approaches to developmental toxicity assessment. When integrated into regulatory science, they can contribute to early safety decisions in clinical development and public health. Coordinated efforts by stakeholders in technology advancement, implementation support, and guideline revision are essential for broader adoption.