Practical Considerations in Determining Adversity and the No-Observed-Adverse-Effect-Level (NOAEL) in Nonclinical Safety Studies: Challenges, Perspectives and Case Studies

Determining the adverse nature of findings from nonclinical safety studies often poses a challenge for the key stakeholders responsible for interpreting the results of definitive toxicity studies in support of pharmaceutical product development. Although there are instances in which responses to treatment clearly indicate intolerability or tissue injury associated with dysfunction; in practice, more often there is uncertainty in characterizing an effect of drug treatment as adverse or not. This is due to the inherent variability in responses of biological test systems to toxicological insults, leaving the ultimate analyses of adversity to individual interpretation and subjectivity. This article is a follow-up to the workshop entitled, "Adverse or Not Adverse?: Thinking process behind adversity determination during nonclinical drug development," conducted at the 58th Annual Meeting of the Society of Toxicology, March 2019 in Baltimore, MD. In this paper, we further discuss and incorporate the perspectives of authors representing different roles, such as Study Director, Study Pathologist, Pharmacology/Toxicology Reviewer (U.S. Food and Drug Administration), and Sponsor in the determination and use of adversity. We also present a practical stepwise approach as an aid in this assessment, and further apply these principles to discuss 10 case studies with different therapeutic modalities and unique challenges.