Composition for the sustained release of a biologically active agent in vivo. The composition comprises microcarriers containing a first solid-phase biocompatible material and a biologically active agent, wherein said microcarriers sustain in vivo release of the biologically active agent. The composition also contains particles of a second biocompatible solid-phase material wherein the second solid-phase material further sustains the in vivo release of the biologically active agent. The invention also relates to a method for sustaining effective serum levels of a biologically active agent in a subject, including forming an injectable dose containing an effective amount of a biologically active agent, wherein the agent is contained in a microcarrier, with a release-period sustaining amount of a solid-phase material. The method further includes administering the injectable dose to the subject.
