Safety assessment of drug impurities for patient safety: A comprehensive review

Drug impurities are undesirable but unavoidable chemicals which can occur throughout the drug life cycle. The safety implications of drug impurities can be significant given that they can impact safety, quality, and efficacy of drug products and that certain drug impurities are mutagenic, carcinogenic, or teratogenic. The characteristics of drug impurities could be specific to drug modalities (e.g., small molecules vs. biologics). The commonly encountered drug impurities include elemental impurity, residual solvent, organic impurity, host cell protein and DNA, residual viral vector, extractable and leachable, and particle. They can cause various adverse effects such as immunogenicity, infection, genotoxicity, and carcinogenicity upon significant exposure. Therefore, the effective control of these drug impurities is central for patient safety. Regulations and guidelines are available for drug developers to manage them. Their qualification is obtained based on authoritative qualification thresholds or safety assessment following the classic toxicological risk assessment. The current review focuses on the safety assessment science and methodology used for diverse types of drug impurities. Due to the different nature of diverse drug impurities, their safety assessment represents a significant challenge for drug developers.