Final answer:
Phase I clinical trials focus on evaluating the safety, tolerability, and pharmacokinetic properties of a new drug in humans. They start with sub-therapeutic doses, which are escalated, and the trials determine a safe dosing range for future studies.
Step-by-step explanation:
The main characteristics of Phase I clinical trials include the initial administration of a drug to humans to assess safety and tolerability. The goal is to investigate the drug's pharmacokinetic properties such as its absorption, bioavailability, and elimination half-life. These trials typically begin with a single sub-therapeutic dose, which is gradually escalated, followed by multiple dose studies. If the drug proves to be not well tolerated, its development is halted. The trials are heavily monitored, allowing researchers to define a safe dosing range and decide if the compound should proceed to subsequent phases.