A hydrophilic biocompatible sustained-release material is disclosed. The material comprises amounts of Pluronic F-127, PEG-400, HPMC and water, effective to produce a composition of sufficiently low viscosity at room temperature to be injectable into an internal body cavity via a tube inserted within a urinary catheter. At body temperature, the material exhibits a much higher viscosity and will stably adhere to the internal surface of a body cavity. As the material dissolves, a therapeutic agent incorporated therein is slowly released to the body cavity, while the material itself is excreted from the body.