Excipients are inactive ingredients that are added to drug formulations to improve their stability, solubility, and bioavailability. While these excipients are generally considered safe, they can have toxic effects at high concentrations or when combined with certain drugs.

The safety evaluation of excipients and formulations is an important part of preclinical studies, as it ensures that the excipients used in the formulation are safe and do not cause adverse effects in animals or humans. The evaluation of excipients and formulations typically involves several steps, including physicochemical characterization, in vitro studies, and in vivo studies.

Physicochemical characterization involves the analysis of the physical and chemical properties of the excipient, such as its solubility, stability, and particle size distribution. In vitro studies are used to evaluate the effects of the excipient on cells or tissues, using assays such as cytotoxicity, genotoxicity, and immunotoxicity. In vivo studies are used to evaluate the effects of the excipient on animals, using endpoints such as mortality, body weight, and organ toxicity.

The safety evaluation of excipients and formulations is typically conducted using a tiered approach, starting with low doses and escalating to higher doses as necessary. The selection of appropriate doses and endpoints is critical to ensure that the study provides meaningful data on the safety of the excipient.

Overall, the safety evaluation of excipients and formulations is a critical step in preclinical studies, as it ensures that the excipients used in the formulation are safe and do not cause adverse effects in animals or humans. The evaluation typically involves several steps, including physicochemical characterization, in vitro studies, and in vivo studies, and is conducted using a tiered approach to ensure the selection of appropriate doses and endpoints.