Polyoxyl 15 hydroxystearate (Solutol HS 15; poly-oxyethylene esters of 12-hydroxystearic acid) is a novel non-ionic surfactant and emulsifier used as a solubilizer in formulation of compounds with low water solubility. Essentially, it is used to enhance the water/aqueous solubility of Class 2 and 4 [Biopharmaceutical Classification System (BCS)] lipophilic molecules. It can also increase the permeability of medium
sized biological molecules/drugs across epithelia.