This invention relates to kits for the preparation of a composition, which comprises a carrier phase that forms an implant or particles in the body, on the body or under physiological conditions. The carrier phase comprises at least one solid carrier material and a solvent, wherein the carrier material and the solvent are stored separately in the kit. The kit can also include an additional liquid phase to aid in forming the particles. An active compound included in the carrier phase is generally released in an extended manner. This invention also relates to compositions prepared from this kit and to methods for the preparation of the kits and the composition.