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# Pfizer Petitions FDA on Premarin Bioequivalence
- URL: https://www.fdaweb.com/pfizer-petitions-fda-on-premarin-bioequivalence/
- Published: 2018-08-31T12:00:00.000Z
- Updated: 2026-09-15T00:29:22.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5142243

Pfizer has petitioned FDA to tighten bioequivalence requirements for any ANDA submitter seeking to gain approval for generic copies of its Premarin (conjugated estrogens) tablets. The [petition](https://www.regulations.gov/contentStreamer?documentId=FDA-2018-P-3325-0001&attachmentNumber=1&contentType=pdf&ref=fdaweb.com) seeks to revise a 12/2014 draft guidance on methods for establishing active pharmaceutical ingredient sameness and bioequivalence for conjugated estrogens. Pfizer had earlier submitted comments on the “fundamentally flawed” guidance, but when FDA did not act on its recommendations, the company decided to submit the petition.

  
The petition urges FDA to require demonstrating sameness for conjugated estrogens using a publicly available liquid-chromatography/mass-spectrometry method that Pfizer developed. The company says the method was developed with input from FDA. “The Pfizer method permits a determination of sameness between a proposed generic product and Premarin based upon the mixture as a whole, and allows for a comparison across each of the different categories of components that make up the API,” the petition says.