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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.

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Methodology has been devised for the testing and evaluation of the mechanistic release of drug or markers from thermosoftening materials, as represented by the Gelucire class of excipients, which could be predictive. Release of a drug (anhydrous theophylline) and a marker (D&C yellow No. 10) was determined using a calibrated stationary disc/rotating fluid system. Of the fourteen commercially available Gelucire excipients, six were investigated in detail (G46/07, G48/09, G50/02, G50/13, G53/10, G62/05) and found to have biphasic release profiles. Lipid soluble materials demonstrated predominantly diffusion-controlled release, while water-dispersible materials absorbed water and showed signs of swelling which led to erosion as an additional component of the release characteristics.