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The solution properties of aqueous ethanol donor solutions were characterized for the particular case of an increased flux nitroglycerin transdermal system. Permeation through porous and nonporous polymer membranes was investigated and modelled. While the permeation of ethanol through the porous membranes is adequately described by theory, clogging of pores occurs in the presence of lactose. Permeation through ethylene vinyl acetate membranes reflects interactions of the solute and solvent with the polymer.

The self-association of insulin monomers into oligomers and macromolecular aggregates leads to complications in the administration of insulin, both in conventional administration and in the development of long-term insulin delivery systems. These problems are aggravated by the tendency of insulin to adsorb onto the surface of solution containers and infusion devices. Furthermore, with insulin infusion devices, shear rates can be generated which can accelerate the self-association and surface adsorption processes. The effects of urea on shear-induced insulin self-association and surface adsorption were investigated. It was found that the addition of a certain concentration range of urea to insulin solutions greatly reduces both insulin self-association and surface adsorption. Circular dichroic studies established that these concentrations of urea also preserve insulin conformation under high shear rates, where conformations are altered without urea. Higher urea concentrations lead to insulin denaturation and accelerated self-association.

An optimal concentration range of aqueous ethanol produces 5-10-fold increases in nitroglycerin flux across skin and ethanol skin permeation that are far greater than reported previously. For aqueous ethanol solutions saturated with nitroglycerin with an ethanol volume fraction less than or equal to 0.7, the flux of nitroglycerin across skin is linear with the ethanol flux and is traced to a linear solubility relationship and a constant diffusion coefficient.