Sustained-release microspheres are spherical entities with particle size distribution between 5 and 250 μm formed by dissolving or dispersing the drug in a polymeric matrix. Among the many existing extended release formulations, microspheres have unique advantages such as gradual release of the drug by degradation of the microspheres after administration, avoidance of blood concentration peaks and valleys, reduction of the dose during the therapeutic cycle, and improvement of the bioavailability of the drug and patient compliance.
Fig. 1 SEM image of microspheres. (Wu et al., 2019)
Advantages of Microspheres
- Delayed release of microspheres can be up to half a year, greatly improving patient compliance by reducing the frequency of administration.
- Microspheres are slowly released at the site of administration to maintain effective blood concentration, reduce blood concentration fluctuations, and reduce toxic side effects.
- Microspheres have special affinity with certain cells and tissues, and can be endocytosed by the reticuloendothelial system of tissues and organs to achieve targeting.
- Microspheres are mainly used for peptide drugs. Compared with the mature chemical drugs, peptide drugs have more room for development and more market potential.
- The route of administration of microspheres is injection, bypassing the first-pass effect, improving bioavailability and reducing the dose of drug delivery.