[Effect of urea on penetration kinetics of vitamin A acid in human skin].

It is well known that urea can considerably increase the release of drugs from ointment bases and that it is one of the most effective penetration promoters for topically applied drugs. In our present study, therefore, we investigated the influence of urea on the penetration kinetics of vitamin A acid (VAA) into the various layers of human skin. When a vehicle containing urea was applied to the skin, we found increased VAA concentrations depending on the penetration of urea. We discuss the significance of the synergistic properties of VAA and urea in the topical treatment of various skin disease.