Physicochemical aspects of controlled release of substituted benzoic and naphthoic acids from Carbopol(R) gels

Drug release from a matrix consisting of a physical mixture of Carbopol and a weak acid is dependent on the influence of the physicochemical properties of the drug on gel formation in the matrix. Water hydrates the polymer in the matrix which results in swelling and the formation of a gel layer. The solubility and ionization properties of the dissolving drug influence the thickness and viscosity of the gel layer. In turn, the properties of the gel layer affect drug release rate by influencing drug diffusivity and the diffusional pathlength. Examination of the physicochemical properties of the drug is an important factor in elucidating the mechanism of release from Carbopol gels.