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# FDA Denies Most of Salix Xifaxin Petition
- URL: https://www.fdaweb.com/fda-denies-most-of-salix-xifaxin-petition/
- Published: 2022-09-06T12:00:00.000Z
- Updated: 2026-09-14T17:58:25.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5152672

FDA has denied all but two requests in a 2/15/21 petition submitted by Salix Pharmaceuticals asking that the agency not approve any 505(j) ANDA referencing any strength of Xifaxin (rifaximin) tablets as the reference-listed drug unless one of five specified bioequivalence and pharmaceutical equivalence criteria is satisfied. The petition listed these potential studies: studies ensuring equivalent *in vivo* bioavailabilty at sites of drug action; *in vitro* dissolution testing for bioequivalence; clinical endpoint bioequivalence studies; systemic safety; and biowaivers. The petition also asked that FDA incorporate the five criteria in a revised draft guidance on rifaximin.

The FDA [response](https://downloads.regulations.gov/FDA-2021-P-0096-0035/attachment%5F2.pdf?ref=fdaweb.com) explains the agency’s rationale for denying most of the requests. For the request that FDA not permit waivers of the pharmacokinetics and clinical endpoint bioequivalence studies, FDA granted the request to the extent that it plans to make such changes to the draft guidance. The letter also grants the request for revision of the draft-specific rifaximim guidance to the extent that the agency plans to remove the biowaiver options in the guidance.