Process for producing microparticles

A process for producing parenterally administrable microparticles containing a biologically active substance, which process comprises:

• a) preparing an aqueous solution of the biologically active substance to be incorporated in the microparticles,
• b) concentrating the biologically active substance into a highly viscous solution thereof, which has the ability of forming droplets which can be handled at room temperature, or into a precipitation thereof in the form of solid particles, by a mixing of the solution obtained in step a) with an aqueous solution of polyethylene glycol (PEG),
• c) optionally washing the concentrated and/or solidified biologically active substance obtained in step b),
• d) mixing the concentrated and/or solidified biologically active substance obtained in step b) or c) with a solution of a biodegradable polymer in an organic solvent,
• e) mixing the composition obtained in step d) with an aqueous solution of a polymer having the ability of forming an emulsion, so as to form an emulsion of droplets of said biodegradable polymer, which contain the biologically active substance as the inner phase in an outer phase of said polymer solution,
• f) causing or allowing the droplets obtained in step e) to solidify into microparticles,
• g) drying the microparticles from step f), and
• h) optionally applying a release-controlling shell of a biocompatible and biodegradable polymer to the dried microparticles from step f).