The present invention relates to preparation of biodegradable microparticles formed from polylactide-polyglycolide copolymers (PLGA) polymer and how to achieve sigmoidal release of active pharmaceutical compound from the microparticles. In particular, the present invention relates to emulsification of an inner/oil phase to an outer/water phase followed by quenching and a single drying step for the preparation of microparticles having a preferred release profile of, preferably basic/nucleophilic compounds such as risperidone. Alternatively the present invention is also suitable for hydrophobic compounds that have poor water-solubility and a high drug loading of >；20%w/w is required. The release profile can be controlled by adjusting the degree of saturation of the outer/water phase with the organic solvent used in the inner/oil phase, the polymer concentration of the inner/oil phase and the temperature at the quenching step. In particular, an initial lag phase and a substantially sigmoidal release profile are achieved by using an outer aqueous phase over saturated with the solvent used in the inner phase at emulsification step, in combination with a low temperature during quenching.
