Drug and excipient diffusion and solubility in acrylate adhesives measured by infrared-attenuated total reflectance (IR-ATR) spectroscopy

Abstract

Infrared-attenuated total reflectance (IR-ATR) was used to measure drug and excipient diffusion in acrylate pressure-sensitive adhesives. The first part describes diffusion of drug and excipient from one adhesive layer to another. The IR-ATR spectrometer is used to continuously monitor the rate at which drug and excipient diffuse into the ‘receptor’ adhesive layer. In this way, the ability of the drug and/or excipient to leave an adhesive can be determined without any influence of receptor fluids or skin membranes. Data is reported here for terpineol and testosterone diffusion in isooctyl acrylate (IOA) and IOA–acrylic acid (AA) adhesives. It is shown that the diffusion rate is much higher in IOA adhesive than in IOA–AA adhesive. The second part describes the use of IR-ATR to measure the solubility of liquids in adhesives. In this method, a liquid excipient is placed in direct contact with an adhesive layer containing no excipient. The IR-ATR spectrometer is used to continuously monitor the rate at which excipient diffuses into the ‘receptor’ adhesive layer. At equilibrium, the IR spectrum can be compared to both the pure adhesive spectrum and the pure excipient spectrum to determine the solubility of the excipient in the adhesive. Data are reported here for terpineol in an IOA adhesive and for several liquids in an IOA–vinyl acetate adhesive.