Phase I clinical study is the first stage of clinical trials in which an investigational drug, biologic, or gene therapy is administered to a small group of human subjects — typically 20 to 100 healthy volunteers or patients — to evaluate its safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD), and to determine the maximum tolerated dose (MTD). Phase I studies are primarily designed to identify dose-limiting toxicities, establish a safe dose range, and inform the design of subsequent Phase II trials, and must be conducted in compliance with Good Clinical Practice (GCP) guidelines and under an approved Investigational New Drug (IND) or Clinical Trial Authorization (CTA)
