Effect of the composition of emulsifiers and the dispersion medium on the properties of bases for semi-solid preparations

The aim. To study the effect of cetostearyl alcohol (CSA) on the rheological properties of bases with different dispersion media, the release of propylene glycol (PG) from them, and the ability of these bases to absorb water. Materials and methods. Micelles of a non-ionic surfactant and its aggregates with CSA in a mixed solvent where the structure of water prevails, mixed solvent PG – macrogol 400 (M400) and hydrophilic bases-vehicles with different dispersion media were studied. The research was carried out by the spin probe method using a probe simulating a cationic surfactant and by rotational viscometry. The microstructure of the bases was studied by optical microscopy. The in vitro release test to study the release of PG and M400 from solutions and bases was performed using vertical diffusion chambers. The content of PG and M400 in the dialysate was determined by gas chromatography according to the validated analytical procedures. The absorption of water by solutions and bases was determined by dialysis through the membrane. Results. CSA, which was the part of the bases together with surfactants in certain ratios, was a significant factor in increasing their rheological parameters, reducing the parameters of PG release during in vitro release tests, as well as reducing water absorption. The mechanisms of such influence are different for bases with different structures of the dispersion medium. In the bases, where the structure of water prevailed, lateral phase separation occurred in the supramolecular structures of surfactant and CSA with the formation of liquid domains of surfactant and solid domains of CSA, which contributed to the formation of coagulation structures. In the mixed non-aqueous solvent PG – M400, surfactant micelles and mixed aggregates of surfactant and CSA molecules were not formed; at 25 oC, surfactants and CSA became separate dispersed phases of suspensions, which contributed to the formation of gels. When CSA was added into an aqueous solution of poloxamer 338, PG, M400 and cationic surfactant, the flow behaviour changed, and the rheological parameters increased, which led to a decrease in the release rate and extended for PG and M400 as well as in the ability to absorb water. The rate and extent of PG release from the solution were greater compared to the M400 release. Conclusions. The addition of CSA in combination with surfactants into the bases for semi-solid preparations is a significant factor for modifying their rheological parameters, the kinetics of PG release from them, and water absorption during experiments in vitro. The mechanisms of such an effect are different and depend on the composition and structure of the dispersion medium of the base