Preparation of microparticles having a selected release profile

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Overview The present invention relates to microparticles having a selected release profile for release of the active agent from the microparticles, and to a method for the preparation of such microparticles.
The release profile refers to the quantity or amount of active agent that is released from the microparticles as a function of time.
Release profiles are typically illustrated as the cumulative release, expressed as a percentage of the total amount of active agent present in the microparticles, as a function of time.
Different clinical applications, and/or different active agents, may require different types of release profiles.
For example, one type of release profile includes an "initial burst," or release of a significant amount of active agent from the microparticles within the first 24 hour period.
The initial burst may then be followed by a substantially linear release profile after the initial burst.
Another type of release profile is a sigmoidal release profile.
As used herein, the term "sigmoidal" refers to a release profile that is substantially "S"-shaped.
As shown, for example, in FIG.
6, a sigmoidal release profile is characterized by an initial lag phase, a steep intermediate release phase, and a flat final release phase.
The inventors have unexpectedly discovered that the release profile of the microparticles can be controlled by adjusting the degree of drying that is performed on the microparticles during their preparation.
Particularly, if an intermediate drying step (between the quench/primary extraction step and the washing step as explained below) is eliminated or is incomplete, then the release profile of the microparticles includes an initial burst followed by a substantially linear release profile.
However, if a substantially complete intermediate drying step is performed on the microparticles, then the release profile will be substantially sigmoidal with an initial lag phase.
After the microparticles undergo the degree of intermediate drying needed for the selected release profile, the microparticles are preferably washed and subjected to a final drying step