[Characteristics of poloxamer thermosensitive in situ gel of dexamethasone sodium phosphate].

Thermosensitive in situ gel is a novel drug delivery system which can form gel in situ after injection of the polymer solution into the body and releases the drug in a controlled manner, thus provides a promising strategy for localized drug delivery. The aim of the present work is to investigate the characteristics including gelation temperature, sol-gel transition temperature (T(s-g)), gel strength, stable viscosity, erosion and drug release behavior of the thermosensitive in situ gel which are composed of different concentrations of poloxamer Pluronic F127 and F68. The gelation temperature was determined by tube-reverse method. Rheological measurements were carried out to evaluate T(s-g), stable viscosity and gel strength. Erosion of the gels and release of dexamethasone sodium phosphate (DSP) from the gels were investigated by membrane-free method and HPLC. Increased F127 concentration in gel decreased the gelation temperature, T(s-g) as well as erosion of the gel and drug release rate, while viscosity and gel strength rose accordingly. However, increased F68 in gel could lead to the opposite result. The poloxamer solution below T(s-g) is Newtonian fluid with comparatively low viscosity, but shows the characteristics of the pseudoplastic fluid when temperature rises near to T(s-g). Drug release was controlled by the erosion of the gel matrix, and both of them followed the zero-order kinetics. An optimized formation containing 22.5% F127 and 2.5% F68 showed more desirable characteristics which meet the clinical requirements and is of potential in future clinical therapy.