Utilizing vehicle imbibition by a microporous membrane and vehicle viscosity to control release rate of salbutamol.

The possibility to control the release rate of salbutamol through the hydrophobic Celgard 2500 polypropylene membrane by varying the composition and the viscosity of hydrophilic drug vehicles was investigated. The use of the polypropylene membrane as a control membrane for reservoir-type drug delivery systems was envisaged and water, glycerol, isopropyl alcohol and ethanol, pure or as binary mixtures were studied as vehicles. With varying composition of the vehicle, a sharp change of its imbibition by the membrane from practically none to a complete filling of the membrane pores occurred, which coincided with a steep rise of the drug permeability for the membrane. From this was inferred that the vehicle-filled pores were the dominant permeation pathway, while when no vehicle was imbibed, transport took place by way of the polymer domain of the membrane. In case of imbibition, the permeation rate could be modulated in a predictable fashion by adjusting the viscosity of the vehicle. This demonstrated that drug release could be controlled by utilizing the in situ interaction of the vehicles with this membrane, leading to imbibition and establishment of a permeation pathway with pre-determined viscosity in the pores of the membrane.