An IND (Investigational New Drug) may be submitted for one or more phases of an investigation. The clinical investigation of a previously untested drug is generally divided into three phases. Although in general the phases are concluded sequentially, they may overlap. The three phases of an investigation are as follows:

Phase 1 includes the initial introduction of an investigational new drug into humans. These studies are usually conducted in healthy volunteers and are designed to determine the metabolic and pharmacological actions of the drug in humans, the side effects associated with increasing doses, and, if possible, to gain early evidence of efficacy. Phase 1 studies also evaluate drug metabolism, serum-activity relationships, and the mechanism of action in humans. The total number of patients included in Phase 1 studies is generally in the range of 20-80.

Phase 2 includes the early controlled clinical studies conducted to obtain some preliminary data on the efficacy of the drug for a particular indication or indications in patients with the disease or condition. This phase of testing also helps determine the common short-term side effects and risks associated with the drug. Phase 2 studies usually involve several hundred patients.

Phase 3 studies are intended to gather the additional information about efficacy and safety that is needed to evaluate the overall benefit-risk relationship of the drug. Phase 3studies also provide an adequate basis for extrapolating the results to the general population and transmitting that information to the drug label. Phase 3 studies usually include several hundred to several thousand patients.

Definitions

• Clinical investigation : any experiment in which a drug is administered or dispensed to one or more human subjects.
• Investigator : an individual under whose immediate direction the drug is administered or dispensed to a subject.
• Sponsor : a person who takes responsibility for and initiates a clinical investigation.
• Sponsor-Investigator : an individual who both initiates and conducts an investigation and under whose immediate direction the investigational drug is administered or dispensed. The term does not include any person other than an individual.
• For more definitions, see Drug Development and Review Definitions.