Natural Gums As Viscosity-Enhancers in Pluronic^® F-127 Thermogelling Solutions

Pluronic^® F-127 (poloxamer 407) is a versatile pharmaceutical excipient, offering many opportunities for designing novel therapeutic systems. One of its applications is the formation of a thermosensitive solution as a base for concentrated suspensions or emulsions. When such uses are considered, the need for viscosity enhancement emerges, especially when a long-term stability of dispersion is expected. This study covers the evaluation of chosen natural gums (Acacia, Xanthan Gum, Tragacanth and Guar Gum) as viscosity and gelation enhancers for thermosensitive Pluronic F-127 solution. The major poloxamer concentration was 17 % (w/w), and the gum additions were in the range of 0.125 - 0.5 %. Solutions were evaluated by rotational rheometry at fixed temperatures (20, 25 and 37 °C), as well as with continuous temperature increase and decrease. These studies were also supplied by visual inspection during the Tube Inversion Method experiments. Xanthan Gum turned out to be the most effective viscosity enhancer, giving transparent and stable formulations, while Tragacanth gave lesser viscosity enhancement and left the formulations slightly turbid. Acacia significantly inhibited the gelation, and Guar Gum revealed a major incompatibility (precipitation) with poloxamer. Irreversible gelation was not observed in any case.