Soluplus solutions as thermothickening materials for topical drug delivery.

Soluplus is a pharmaceutical excipient used primarily in the manufacture of solid dispersions. The polymer also exhibits interesting rheology in aqueous solution, increasing in viscosity as the solution is warmed. This material could have application topical drug delivery to sites including the skin, vagina, rectum or nasal mucosa, where the increase in viscosity allows for improved retention. However, there exists very little information surrounding this “thermothickening” phenomenon and the effect of solution composition on temperature-dependent rheology. In this study, the effect of soluplus concentration, salt inclusion, ethanol addition, and pH on temperature-dependent rheology was measured. The rheology of the solutions was unaffected by pH over the range tolerated by the skin (pH 4–7), but the inclusion of ethanol rapidly negated the thermothickening effect. “Salting out” of the solutions resulted in a depression of gelation temperatures, and an increase in both storage and loss moduli of the solutions. 30% (w/v) soluplus in 1 M NaCl or KCl was identified as a potential thermothickening agent for topical drug delivery.