Phase 1 Trial
Definition
The first stage of clinical testing in humans, primarily designed to evaluate the safety, tolerability, and pharmacokinetics of a new drug, typically in a small number of healthy volunteers or patients.
Phase 1 Trial
A Phase 1 clinical trial is the earliest stage of testing a new drug in human subjects. These trials are primarily designed to evaluate safety, tolerability, and pharmacokinetics rather than therapeutic efficacy. Phase 1 studies typically enroll a small number of participants, often between 20 and 100, and may include healthy volunteers or patients with the target condition, depending on the drug’s risk profile and mechanism of action.
Phase 1 trials commonly employ single ascending dose (SAD) and multiple ascending dose (MAD) designs. In SAD studies, small groups of participants receive a single dose of the drug, starting at very low levels predicted from preclinical data, with each successive group receiving a higher dose. MAD studies follow a similar escalation pattern but involve repeated dosing to assess accumulation and steady-state pharmacokinetics. These designs allow researchers to identify the maximum tolerated dose and characterize dose-limiting toxicities.
For retatrutide, the Phase 1 first-in-human study established the drug’s safety profile at initial dose levels, characterized its pharmacokinetic parameters (including the approximately six-day half-life), and provided early signals of biological activity including glucose lowering and weight reduction. These data informed the dose selection for subsequent Phase 2 studies.