Prolonged Gel Delivery to Oral Cavity from a Silicone Tube: In Vivo Assessment

<b>Objectives</b>: This study evaluated the comfort of using silicone tubes installed in the oral cavity as a reservoir for a hydrogel that allows for a slow delivery of the active substance acting locally or systemically. <b>Methods</b>: Perforated silicone tubes 8 cm long with two internal diameters were used: T1 (1.5 mm) and T2 (2.4 mm). The reservoirs were filled with hydrogel placebo formulations: carbomer 1.5% (C), hydroxyethylcellulose 4% (HEC), or hydroxypropylmethylcellulose (hypromellose) 3% (HPMC). Physical parameters of the gel were determined with a viscometer and a texture analyzer. During 4 h of application, the volunteers reported sensory perceptions, and the rate of gel erosion was evaluated. The results were correlated with the viscosity, rheology, and dissolution rate of the gels measured in vitro. <b>Results</b>: Volunteers reported only mild discomfort wearing the device, preferring smaller-sized tubes. The tubes were easy to apply and generally comfortable, with no reports of significant discomfort. Despite similar viscosity and rheology, the polymer type had a significant impact on erosion rate, both in vitro and in vivo. After 4 h of application in vivo, more than 90% of the carbomer gel remained in the tube, while in the case of less cohesive HPMC or HEC gels, this was about 50%. A statistically significant correlation was observed between the in vitro and in vivo mean erosion percentages for the HEC and HPMC gels. <b>Conclusions</b>: This study supports the use of silicone tubes as effective reservoir devices for prolonging the residence time of drug formulations in the oral cavity.