Effect of pH on drug release between sodium salicylate-Eudragit compound and gastric liquid: modelling of the process

The effect of the pH of synthetic gastric liquid on drug release has been studied by soaking sheets made of sodium salicylate previously dispersed in a polymer matrix. Eudragit RS plays the role of polymer and binder. The liquid enters the polymer and dissolves the drug, and then the drug is released into the liquid. Both these transfers are controlled by diffusion under transient conditions, and diffusivity is concentration-dependent. The value of the pH of the synthetic gastric liquid was found to be of great importance for the diffusivities and the amount of matter transferred at equilibrium. The model described was used verify the rate of matter transferred for various values of pH ranging from 1.2 to 7. A law accurately described variation of diffusivity with the pH of the liquid. Profiles of concentration of drug and liquid were calculated for various pH values.