Defining Acceptable Impurity Levels For Drug Substances In GLP Toxicology Studies

GLP toxicology studies play a pivotal role in setting safe starting doses for first‑in‑human trials, yet clear regulatory guidance on impurity limits for preclinical drug substance is limited. A common assumption is that toxicology material should be as pure as possible, but excessive purification can undermine the relevance of safety data. A more effective strategy focuses on producing toxicology batches with impurity profiles that closely resemble those expected for clinical material. This alignment enables impurities to be toxicologically qualified early and strengthens confidence that nonclinical findings will translate to the clinic. Using representative synthetic routes, purification methods, and manufacturing scale helps ensure consistency across development stages. Well‑characterized non‑GMP batches can also support additional activities such as stability studies, reference standard preparation, and early formulation work. By prioritizing impurity relevance over maximum purity, development teams can generate more meaningful toxicology data, streamline progression into clinical phases, and reduce the risk of unexpected findings later in development.