Disclosed is a pharmaceutical composition which is suitable for ophthalmic use and which comprises one or more prostaglandin derivatives or salts such as bimatoprost, travoprost, latanoprost or unoprostone a stabilizing amount of a polyethylene glycol hydroxystearate (such as solutol HS 15) optionally an oil such as castor oil, and a pharmaceutically acceptable vehicle and wherein the pharmaceutically acceptable vehicle is free of quaternary ammonium compounds.
