Final answer:
The starting dose in Phase I clinical trials of cytotoxic drugs is based on pharmacokinetic and toxicological studies, aiming to establish a safe and tolerated dosing range while considering properties like bioavailability and elimination half-life.
Step-by-step explanation:
The starting dose of a Phase I study of cytotoxic drugs is usually determined through a process that considers data obtained from pharmacokinetic and toxicological studies. These studies are essential to evaluate various drug parameters such as absorption, distribution, metabolism, elimination half-life, and bioavailability. The starting dose is often a single sub-therapeutic dose that has shown to be safe in animal models. The dose is then gradually escalated in human subjects while closely monitoring safety, efficacy, and pharmacokinetic profiles to define the safe dosing range. If a drug candidate reveals undesirable pharmacokinetic properties, such as poor bioavailability or inappropriate elimination half-life, it may be dropped from development.