Evaluation of a combined polymer system for use in relieving the symptoms of xerostomia.
OBJECTIVE: The aim of this series of studies on rheological, sensory, and mucoadhesive properties was to evaluate the potential of using a combined polymer system to more closely represent the adaptive nature of saliva, while providing long lasting relief from the symptoms of xerostomia. METHODOLOGY: The rheological investigations were conducted on 1% polymer solutions 24 hours after preparation, during which time they were stored in sealed glass containers at room temperature. The rheometer was controlled via peltier to 35 degrees C +/- 0.1 degrees C, and a shear rate range of 0.1 to 300 s(-1) was applied; thirty measurements were taken during each run. Eight panelists were recruited from the in-house sensory panel at GlaxoSmithKline (GSK) Weybridge to take part in the sensory evaluation. A brief training session was conducted at the start of the study in order to standardize the panelists' responses to the sensory term "tacky." For each test, panelists were given 10 ml of the respective polymer solution and instructed to swirl this solution around their mouths for 20 seconds before expectorating. The panelists were then asked to evaluate the solution in terms of "tack," measured by tapping the tongue on the roof of the mouth. A new formulation, based upon the rheology and sensory testing, was evaluated versus other commercially available sprays for the relief of xerostomia. The new formulation, named OASIS, contains a combination of Xanthan gum, carboxymethyl cellulose and a polyvinyl pyrollidone backboned polymer. To evaluate mucoadhesion of this final product, a 16 mm diameter cylindrical aluminium probe was selected. The probe and the base platform were both coated with a thin layer of artificial polyurethane membrane to more closely mimic the oral mucosal surface. The probe was set to travel downward at 2.0 mm/sec until it made contact with the base platform with a force of 1000 g. The two surfaces were then left in contact for 30 seconds before the probe receded from the base platform at 0.5 mm/sec to a distance of 10 mm. A plot of force versus distance was obtained, and the area under the curve (defined as the Work of Adhesion, energy required to separate the two surfaces) was used as a measure of the mucoadhesion of the materials. RESULTS: For rheology, the Xanthan gum solution showed high initial viscosity of 32 Pa.s at 0.1 s(-1) with rapid shear thinning to 4.0 Pa.s. By 1.2 s(-1) the viscosity continued to drop with increasing shear rate to 0.05 Pa.s at 300 s(-1). For the sensory assessment, the CMC single solution was perceived to be significantly (p = 0.04) more tacky than the CMC + PVP solution. The Xanthan + PVP solution was perceived to be less tacky (slightly/moderately tacky) than the Xanthan solution (moderately tacky). The Xanthan + CMC + PVP solution was perceived to be less tacky (slightly tacky) than the Xanthan + CMC solution (moderately tacky). Overall, there was a significant difference in favor of the inclusion of PVP across the products (p = 0.038), which was also shown to be a consistent effect across the different polymer solutions. CONCLUSION: The sensory solution work indicates that the addition of a PVP backbone polymer within an anionic polymer solution (OASIS) enables higher concentrations of mucoadhesive polymer to be included within a dry mouth formulation, while at the same time giving improved mouth-feel due to reduced tack.