Maximum tolerated dose (MTD) is the highest dose of a drug that doesn't cause unacceptable side effects or overt toxicity in a specific time period.
Determining the MTD during preclinical development is crucial for two main reasons: to ensure patient safety in future clinical trials and to guide the design of those trials.

Pharmacokinetics (PK) in rodents is the quantitative study of the time course of drug disposition. It describes the fate of a xenobiotic compound within a living organism. This involves determining the concentration of the drug in systemic circulation and at its site of action over a given period, providing a foundation for understanding the relationship between drug dose, exposure, and effect.