A Note on the Solubility of Progesterone in Aqueous Polyethylene Glycol 400

Abstract

The solubility curve of progesterone in aqueous polyethylene glycol (PEG) 400 at ambient room temperature (～25°C) is bimodal, a break occurring at approximately 60% w/w PEG.

It is speculated that the presence of unbound water in the PEG 400/water system depresses the solubility of progesterone in PEG 400 disproportionately.