Abstract

Microcapsules particularly those less than 300 microns in size are provided which are adapted for injection by conventional means to afford controlled release of the encapsulated drug material, such as a narcotic antagonist, an antibiotic or the like, over a prolonged period. The microcapsules are characterized by a solid core material of a solid, injectable drug material and a wall material engulfing the core material and composed of a polymer material such as a bioabsorbable polymer material. The microcapsules are made by providing a system containing a mixture of particles of a solid, injectable drug material and a solution of a bioabsorbable polymer material in a solvent in which the drug material is substantially insoluble. The system is treated to induce phase separation of the bioabsorbable polymer material from the solution by the addition to the system of a phase separation agent at a temperature at least as low as -30° C. Phase separation may also be carried out at room temperature, but in either event, isolation of the microcapsules formed during the phase separation should be carried out at a temperature at least as low as -30° C. The system is maintained in an agitated condition until the walls of the microcapsules constituted by the bioabsorbable polymer are substantially solidified in order to avoid aggregation or agglomeration of the microcapsules into larger capsules. The microcapsules are ready for injection, for example by being suspended in an aqueous suspending medium, upon being isolated from the system.