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# Changes Suggested for PBPK Guidance
- URL: https://www.fdaweb.com/changes-suggested-for-pbpk-guidance/
- Published: 2017-01-31T12:00:00.000Z
- Updated: 2026-09-14T22:03:44.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5137870

Merck says that the scope of a draft FDA guidance on the format and content of physiologically based pharmacokinetic (PBPK) analyses should be expanded since such modeling supports sNDAs and sBLAs as well as INDs, NDAs, BLAs, and ANDAs. Also, the letter [says](https://www.regulations.gov/document?D=FDA-2016-D-3969-0011&ref=fdaweb.com), FDA acknowledges that the depth and breadth of PBPK analyses at each stage may vary due to the availability or quantity of data and thus the guidance should allow for more flexibility when such data are not available. It further calls for adding a section on “Equations Describing the PBPK Model,” with an explanation for which each model element was selected.

The Critical Path Institute [asks](https://www.regulations.gov/document?D=FDA-2016-D-3969-0012&ref=fdaweb.com) if there are specific format requirements such as minimum font size, line spacing, or file format that the agency want to specify and also asks for clarification of whether a table of contents is needed.

Line-by-line specific comments were provided by the [International Consortium for Innovation and Quality in Pharmaceutical Development](https://www.regulations.gov/document?D=FDA-2016-D-3969-0005&ref=fdaweb.com) on behalf of 23 companies participating in a consortium work group, and [Sanofi](https://www.regulations.gov/document?D=FDA-2016-D-3969-0013&ref=fdaweb.com).