Microparticulate systems such as microspheres, microcapsules, or any particle in a micrometer scale (usually of 1–1000 µm) are widely used as drug delivery systems, owing to their higher therapeutic and diagnostic performance compared to conventional drug delivery forms.
These systems can be manufactured with many raw materials, especially polymers, most of which have been effective in improving the physicochemical and biological properties of the active compounds.
Structurally, microparticles are divided into two large groups, that is,
- microspheres, in which the active compound and the raw material are dispersed or dissolved homogeneously, and
- microcapsules, in which there is a membrane enclosure delimiting and encompassing the nucleus—solid, liquid or gaseous—where the active principle is deposited.
Other variants of microparticles can be manufactured with different multilayers, nuclei, or irregular shapes.
There are several manufacturing techniques like phase separation, double emulsion, spray-drying and cryogenic spray-drying and the selection of a particular technique is dependent on the physicochemical properties of the active drug, polymer, and the intended use of the drug product.
Microspheres are typically manufactured by an aseptic process because terminal sterilization (heat sterilization and gamma irradiation) results in degradation of the microspheres, loss of polymer molecular weight, and hence, performance.
The in-vitro release is a key quality attribute to evaluate and demonstrate acceptable product performance besides the size, shape and surface morphology in the drug product.
Thus, it requires careful development of test methods and acceptance criteria for the specifications.
Description of scope and application:
The focus of this General Chapter is to describe critical quality attributes and performance characteristics like universal tests, specific tests, performance tests and intended to provide guidance on acceptance limits wherever applicable that are generally necessary for Microsphere preparations as well as selected specific requirements for Microspheres not mentioned by other General Chapters.
USP is requesting early input from stakeholders on this proposal for a new General Chapter, <1156> Product Quality and Performance Tests for Microspheres, which is planned to be published for comment in the Pharmacopeial Forum.
Anticipated implementation timing: Routine (six months after USP-NF publication).
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