Determination of the rheological optimum oral gels

Oral gels are a promising dosage form, especially in pediatric and geriatric practice. They provide higher stability, dosage accuracy and dosage convenience compared with liquid dosage forms. The aim of the study was to determine the rheological optimums for 3 oral gels registered in the Russian Federation (Phosphalugel®, Pepsan-R®, Transulose®), based on the analysis of structural and mechanical parameters. Rheological parameters were measured on the coaxial rotation viscometer LamyRheologyRM 200 at a temperature of 20 °C with shear rates from 0 to 300 s-1. Approximation of the obtained results was carried out according to the Casson rheological model, as the most suitable for viscous-plastic systems with non-Newtonian flow type and yield strength. It was shown that the rheological characteristics of the studied samples lie in a wide range (yield strength from 7.42 to 70.5 Pa; plastic viscosity from 0.080 to 0.528 Pa*s), the lowest values of plastic viscosity and yield strength are possessed by the Phosphalugel® (0.080 Pa s and 7.42 Pa respectively), the largest - by the Transulose® (0.528 Pa s and 70.5 Pa). All drugs in the form of oral gels were highly thixotropic, had a pseudoplastic non-Newtonian type of flow. Basing on the obtained viscosity curves, a rheological optimum of oral gels was built. At a temperature of 20 °C, the optimal values of the dynamic viscosity of oral gels at a shear rate of 30 s-1 lie in the range from 0.56 to 4.94 Pa s, and at a shear rate of 300 s-1 - from 0.20 to 1.53 Pa s. Applicability of the obtained optimums was proven to be effective in designing oral gels based on mono- or polycomponent matrices. It is expected, that the following rheological approach to designing semisolid oral dosage forms will allow to produce dosage forms with optimal biopharmaceutical characteristics.

oral gels, jelly, rheology, rheological optimum, plastic viscosity, yield strength, Casson fluid model