Evaluation of release from selected thermosoftening vehicles

Release of D&C Yellow No. 10 and anhydrous theophylline have been determined from a thermosoftening, hydrophilic matrix, Gelucire 50/13, incorporating a water-soluble additive, polyethylene glycol 4000. As additive level increased, release also increased. The effect of mixtures of Gelucire 50/13 (G50/13) and Gelucire 50/02 (G50/02) on release was also investigated as a function of temperature and pH. As the level of G50/02 increased, release decreased and became predominantly diffusional. As temperature was increased, release changed from diffusion to a mixed model of both diffusion and erosion. At basic pH, release from these composite systems became more erosional in character, possibly reflecting partial hydrolysis of the ester-linked matrices. Diffusion coefficients and apparent diffusion coefficients were calculated in G50/02 and G50/13 matrices, respectively, and were in agreement with published data.