An improved topical formulation for urea

The solubility of urea in different polar solvents was studied by means of determination of their dielectric constants. The most appropriate solvents turned out to be water and a water/propylene glycol (1:1 in volume) mixture. The best solvents were then used in the study of different semisolid vehicles for topical use (cetylic excipient, Beeler's base and Carbopol gel), which show different physicochemical characteristics. The final formulation contained a 40% (w/w) concentration in urea, since this value is most often used in Dermatology and, at the same time, it is the most problematic from a technological point of view. The stability of the different preparations was investigated by conductimetric and rheological determinations. The results are discussed in terms of both the solubility and stability of the active principles and the organoleptic and rheological characteristics of the final preparations.