Under 21 CFR 312.21, Phase 1 requirements for a clinical investigation cover a first-in-human study of roughly 20 to 80 subjects, conducted under an active Investigational New Drug (IND) application, designed to characterize the drug’s metabolism and pharmacological actions, identify side effects associated with increasing doses, and, where possible, gather early evidence of effectiveness.1eCFR. 21 CFR 312.21 – Phases of an Investigation Safety is the dominant concern, but the regulation is broader than a pure safety exercise, and the operational obligations that attach to it, from IND filing through adverse event reporting, are where sponsors most often run into trouble.
The Four Objectives Phase 1 Must Meet
The regulation names four things a Phase 1 study is designed to accomplish. It must determine the drug’s metabolism and pharmacologic actions in humans, identify side effects associated with increasing doses, gather pharmacokinetic and pharmacological data sufficient to design well-controlled Phase 2 studies, and, if possible, gain early evidence on effectiveness.1eCFR. 21 CFR 312.21 – Phases of an Investigation
That last objective surprises people who think of Phase 1 as safety-only. The regulation uses the phrase “if possible, to gain early evidence on effectiveness,” which acknowledges that preliminary efficacy signals can shape the program even when they aren’t the point.
Phase 1 also covers a second category of study: investigations that use the drug as a research tool to explore biological processes or disease mechanisms, including drug metabolism studies and structure-activity relationship analyses.1eCFR. 21 CFR 312.21 – Phases of an Investigation These aren’t always aimed at commercialization but still fall under Phase 1 rules.
How Many Subjects and Who Qualifies
Phase 1 studies typically enroll 20 to 80 subjects. That range is a guideline rather than a ceiling, and actual enrollment depends on the drug.1eCFR. 21 CFR 312.21 – Phases of an Investigation
Sponsors may enroll either healthy volunteers or patients with the target disease. Healthy volunteers give researchers a clean baseline for measuring pharmacokinetics and side effects without the confounding effects of underlying illness. For drugs targeting cancer or other severe conditions, dosing healthy people would be unethical given the expected toxicity, so those trials recruit patients directly.2U.S. Food and Drug Administration. Step 3: Clinical Research
The IND Filing That Has to Come First
No Phase 1 dosing can happen without an IND in effect. The sponsor files the IND with FDA, and the application must include a cover sheet, a general investigational plan, an investigator’s brochure, the Phase 1 protocol, chemistry and manufacturing information showing the drug can be produced consistently, and preclinical pharmacology and toxicology data from animal studies supporting the reasonable safety of human testing.3eCFR. 21 CFR 312.23 – IND Content and Format
Once the IND is submitted, the sponsor must wait 30 days before dosing any human subject. During that window FDA reviews the submission and can impose a clinical hold. If 30 days pass without FDA objection, the IND takes effect and the trial may start. FDA may also authorize an earlier start.4eCFR. 21 CFR 312.40 – General Requirements for Use of an Investigational New Drug The 30-day wait is not a formality. Incomplete preclinical data or a weak protocol can produce a hold that delays a program for months.
Informed Consent for Every Participant
Every enrolled subject must give informed consent, and 21 CFR 50.25 lists what they must be told first. Required disclosures include that the study is research, how long participation will last, what procedures will be performed, foreseeable risks, potential benefits, alternative treatments, how confidentiality will be handled, and who to contact with questions or in case of injury.5eCFR. 21 CFR 50.25 – Elements of Informed Consent
Two elements matter in a particular way for Phase 1. For research involving more than minimal risk, the consent document must state whether compensation or medical treatment is available if a participant is injured. And the participant must be told they can withdraw at any time without penalty or loss of benefits.5eCFR. 21 CFR 50.25 – Elements of Informed Consent The withdrawal disclosure is not boilerplate. In patient populations with few treatment options, the pressure to remain enrolled can be significant, and the regulation makes sure subjects know they aren’t locked in.
When applicable, additional disclosures cover unforeseeable risks, circumstances in which the investigator might end a subject’s participation without consent, extra costs to the participant, and a commitment to share significant new findings that could affect willingness to continue. For applicable clinical trials, the consent form must also include a standardized statement that trial information will be posted on ClinicalTrials.gov.5eCFR. 21 CFR 50.25 – Elements of Informed Consent
Safety Reporting Deadlines
Continuous safety monitoring runs throughout Phase 1, and the reporting clocks are strict.
The sponsor must notify FDA and all participating investigators of certain safety information no later than 15 calendar days after determining that the information qualifies for reporting.6eCFR. 21 CFR 312.32 – IND Safety Reporting That 15-day category includes serious and unexpected suspected adverse reactions, findings from other clinical or epidemiological studies that suggest a significant risk, animal or in vitro test results indicating human risk, and any clinically important increase in the rate of a serious suspected adverse reaction.
Fatal or life-threatening suspected adverse reactions carry a shorter clock: the sponsor must report them to FDA within 7 calendar days of first learning about them.6eCFR. 21 CFR 312.32 – IND Safety Reporting Missing either deadline can trigger regulatory action.
A “serious” adverse event means any outcome resulting in death, a life-threatening situation, inpatient hospitalization or prolongation of existing hospitalization, persistent or significant incapacity to conduct normal life functions, or a congenital anomaly or birth defect.7U.S. Food and Drug Administration. IND Application Reporting: Safety Reports The definition is broad on purpose. FDA wants sponsors erring toward reporting.
IRB Review Before and During the Study
Before any subject is enrolled, the protocol must be reviewed and approved by an Institutional Review Board. The IRB has authority to approve the study, require modifications, or reject it, and it evaluates whether risks are reasonable in relation to anticipated benefits, whether the consent process is adequate, and whether subject selection is equitable.8U.S. Food and Drug Administration. Institutional Review Boards Frequently Asked Questions
IRB oversight continues during the trial. The board conducts periodic reviews, and the investigator must submit proposed protocol changes for approval. In Phase 1 this matters, because the drug’s safety profile is largely unknown at the start and information from early cohorts can change the risk picture for those that follow.
When FDA Can Put a Phase 1 Trial on Hold
FDA can stop a Phase 1 study at any point through a clinical hold. Under 21 CFR 312.42, the primary grounds for holding a Phase 1 investigation are:
- Human subjects are or would be exposed to an unreasonable and significant risk of illness or injury.
- The clinical investigators named in the IND lack the scientific training and experience to conduct the study as described.
- The investigator brochure is misleading, erroneous, or materially incomplete.
- The IND does not contain sufficient information to assess the risks to subjects.
A separate ground applies to drugs intended for life-threatening diseases affecting both sexes: FDA can hold a study that excludes men or women of reproductive potential solely because of a risk or potential risk of reproductive or developmental toxicity, subject to certain exceptions.9eCFR. 21 CFR 312.42 – Clinical Holds and Requests for Modification
A hold stops all dosing. The sponsor cannot resume until it addresses the deficiencies and FDA notifies it that the hold has been lifted.
What Phase 1 Has to Produce to Reach Phase 2
Advancing to Phase 2 requires enough data to justify testing in a larger patient population. That means a documented maximum tolerated dose or biologically effective dose, the side-effect pattern across dose levels, and the pharmacokinetic parameters needed to design Phase 2 dosing regimens. The regulation itself states that Phase 1 should yield “sufficient information about the drug’s pharmacokinetics and pharmacological effects to permit the design of well-controlled, scientifically valid, Phase 2 studies.”1eCFR. 21 CFR 312.21 – Phases of an Investigation
Procedurally, the sponsor submits the new protocol as an amendment to the existing IND. A Phase 2 study may begin once the sponsor has submitted the protocol to FDA and an IRB has approved it; these two steps can occur in either order.10eCFR. 21 CFR 312.30 – Protocol Amendments There is no separate 30-day waiting period for a protocol amendment, but FDA keeps the authority to place a clinical hold if it finds problems with the new protocol.