Drug molecules as probes for studying the compatibility between gels and mucous tissue with dielectric spectroscopy.

In this interdisciplinary study low-frequency dielectric spectroscopy is used to assess the possibilities of intimate surface contact between a polymer gel and mucous tissue, which is generally considered to be the first step in the mucoadhesion process. The dielectric responses of six different gels, made from Carbopol 934 or Pluronic F-127 and containing 15 mM of a drug compound, either atenolol, alprenolol, or naproxen, were measured together with the responses of freshly excised porcine nasal mucosa and of systems made by combining the two. An analytical procedure is presented, which enables the dielectric response arising from the drug ions to be extracted. The drug ions are used as probes for measuring the ease, in terms of conductivity, with which they can pass the interface between the gel and the mucus layer. The results can be described by a compatibility factor that provides us with an assessment of the likelihood of intimate surface contact. The compatibility factors found in this study were generally higher for the Carbopol 934 gels than for the Pluronic F-127 gels, which is in agreement with the results of a previous study where sodium and chloride ions were used as probes for measuring the compatibility. Naproxen exhibited the largest difference in compatibility factor between the two gels; the highest compatibility factor of all systems was found for the Carbopol 934 gel whereas the gel based on Pluronic F-127 gave a value of approximately zero. This may partly be explained by interactions between the drug ions and the polymers.