Change Premarin Prescribing Info to Include Equilin: Petition

Diamond Research Foundation founder Beth Rosenshein is petitioning FDA to update the Indications and Usage section of the labeling for Pfizer’s Premarin (conjugated estrogens tablets) “to include pertinent information about the estrogen hormone equilin.” The petition says equilin is a major component of Premarin, comprising 22%-30% of its ingredients.

It says the estrone in Premarin can convert to estradiol via the enzyme 17β-hydroxysteroid dehydrogenase type 1. It cites a 1999 journal article stating that equilin blocks that enzyme in vitro, and it is thus likely that it would block the enzyme in vivo.

“Since there is a possibility that the equilin in Premarin could block estrone converting to estradiol in vivo,” the petition says, “it is important to include this information in the full prescribing information for Premarin tablets.”