Effect of medium on the permeation of drugs through polymeric membranes: Competition between swelling and partition

In the present work, the effect of medium on the drug permeation rate through polymeric membranes was investigated, The medium used in this work was ethanol-water solution of which the property can be adjusted by varying the ethanol composition. The membrane used was the polyurethane membrane and the model drug was nitroglycerin. The results indicate that an increase in the ethanol concentration in medium can have two effects: it can increase the nitroglycerin solubility in the donor and thus decrease the partition coefficient, and it can increase the degree of swelling of the polyurethane membrane and thus result in higher nitroglycerin diffusivity. When the ethanol concentration is lower than 65 wt%, the effect of partition dominates and increasing ethanol concentration results in decreasing nitroglycerin permeability. On the other hand, when the ethanol concentration is higher than 65 wt%, the effect of swelling on diffusivity dominates and increasing ethanol concentration results in increasing nitroglycerin permeability. Due to the competition between these two effects, a minimum nitroglycerin permeability occurs when the ethanol concentration is around 65 wt%.