21 CFR Part 320 · Bioavailability and Bioequivalence Requirements

21 CFR 320.31

Applicability of requirements regarding an “Investigational New Drug Application.”

21 CFR 320.31 is the regulation titled “Applicability of requirements regarding an ‘Investigational New Drug Application.’” in 21 CFR Part 320, Bioavailability and Bioequivalence Requirements. Since 2021, 4 FDA warning letters have cited it.

Letters citing it
4 since 2021
Jan 1 to Oct 30, 2026
3 against 0 on the same dates in 2025
Most often cited with
21 CFR 312.60, in 4 letters
Closed out
0% of these letters have a published close-out
See the 4 letters citing 21 CFR 320.31 →

Letters citing it, by year issued

All are drug letters. 2026 runs to Oct 30, 2026. Pick a year to see its letters.

  1. 02021
  2. 02022
  3. 02023
  4. 02024
  5. 12025
  6. 32026

The regulation

Read the text of 21 CFR 320.31 (eCFR, as of Sep 1, 2026)

(a) Any person planning to conduct an in vivo bioavailability or bioequivalence study in humans shall submit an “Investigational New Drug Application” (IND) if:

(1) The test product contains a new chemical entity as defined in § 314.108(a) of this chapter; or

(2) The study involves a radioactively labeled drug product; or

(3) The study involves a cytotoxic drug product.

(b) Any person planning to conduct a bioavailability or bioequivalence study in humans using a drug product that contains an already approved, non-new chemical entity shall submit an IND if the study is one of the following:

(1) A single-dose study in normal subjects or patients where either the maximum single or total daily dose exceeds that specified in the labeling of the drug product that is the subject of an approved new drug application or abbreviated new drug application.

(2) A multiple-dose study in normal subjects or patients where either the single or total daily dose exceeds that specified in the labeling of the drug product that is the subject of an approved new drug application or abbreviated new drug application.

(3) A multiple-dose study on an extended release product on which no single-dose study has been completed.

(c) The provisions of parts 50, 56, and 312 of this chapter are applicable to any bioavailability or bioequivalence study in humans conducted under an IND.

(d) A bioavailability or bioequivalence study in humans other than one described in paragraphs (a) through (c) of this section is exempt from the requirements of part 312 of this chapter if the following conditions are satisfied:

(1) If the study is one described under § 320.38(b) or § 320.63, the person conducting the study, including any contract research organization, must retain reserve samples of any test article and reference standard used in the study and release the reserve samples to FDA upon request, in accordance with, and for the period specified in, § 320.38;

(2) An in vivo bioavailability or bioequivalence study in humans must be conducted in compliance with the requirements for institutional review set forth in part 56 of this chapter, and informed consent set forth in part 50 of this chapter; and

(3) The person conducting the study, including any contract research organization, must notify FDA and all participating investigators of any serious adverse event, as defined in § 312.32(a), observed during the conduct of the study as soon as possible but in no case later than 15 calendar days after becoming aware of its occurrence. Each report must be submitted on FDA Form 3500A or in an electronic format that FDA can process, review, and archive. FDA will periodically issue guidance on how to provide the electronic submission (e.g., method of transmission, media, file formats, preparation and organization of files). Each report must bear prominent identification of its contents, i.e., “bioavailability/bioequivalence safety report.” The person conducting the study, including any contract research organization, must also notify FDA of any fatal or life-threatening adverse event from the study as soon as possible but in no case later than 7 calendar days after becoming aware of its occurrence. Each notification under this paragraph must be submitted to the Director, Office of Generic Drugs in the Center for Drug Evaluation and Research at FDA. Relevant followup information to a bioavailability/bioequivalence safety report must be submitted as soon as the information is available and must be identified as such, i.e., “Followup bioavailability/bioequivalence safety report.” Upon request from FDA, the person conducting the study, including any contract research organization, must submit to FDA any additional data or information that the agency deems necessary, as soon as possible, but in no case later than 15 calendar days after receiving the request.

[57 FR 18000, Apr. 28, 1992, as amended at 58 FR 25927, Apr. 28, 1993; 67 FR 77674, Dec. 19, 2002; 75 FR 59963, Sept. 29, 2010]

Text from eCFR as of Sep 1, 2026.

Cited alongside it

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Latest letters citing it

The 3 letters citing 21 CFR 320.31 that FDA posted most recently.

See the 4 letters citing 21 CFR 320.31 →
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