Microparticle preparations, also named microparticle drug delivery system (MDDS), refer to solid, liquid, or gaseous drug preparations which consist of particles made from drugs or/and appropriate carriers (commonly biodegradable materials) in a certain particle size (micron scale or nanoscale) using certain dispersion and embedding techniques. They can cover up the drugs’ unpleasant odor and taste, solidify liquid drugs, reduce the change to drug formation, improve solubility of drugs that are difficult to dissolve, improve drug bioavailability/stability, reduce drug adverse reactions, delay drug release, increase targeted delivery, etc.
According to the classification principle of pharmaceutical dispersion system, the dispersion systems with unit diameters ranged from 10-4m to 10-9m are classified as particle dispersion systems. Among them, the dispersion with unit diameters from 1 um to 500 um are MDDS of thick (micron) dispersion systems, including microcapsules, microspheres, and sub-microemulsions, etc. Dispersion systems with unit diameters less than 1,000 nm are MDDS of nano-dispersion systems, including liposomes, nano-emulsions, nanoparticles, and polymeric micelles, sub-microemulsions, etc. Microcapsules, microspheres, sub-microemulsions, liposomes, nano-emulsions, nanoparticles, and polymeric micelles can be used as drug carriers.
With the development of modern preparation techniques, preparations of microparticle carriers are increasingly used in clinics. The drug administration routes include external use, oral dosing and injection. Microparticle preparations for external use or oral dosing generally increase drug permeability across biomembranes, such as skin, mucosa, etc. Microparticle preparations for injections generally possess delayed, controlled or targeted-release characteristics. Drug preparations with targeted characteristics are usually named targeted preparations.
Targeted preparations refer to a category of new preparations that use carriers to concentrate the drug from circulatory system in or near the targeted organs, tissues, cells and intracellular structures. They can enhance the therapeutic effects and significantly decrease the adverse drug reaction on other tissues, organs and the whole body. Targeted preparations can be divided into three types:
① Targeted preparations of the first class are those which deliver the drug in the capillary vessel bed of the targeted organs;
② Targeted preparations of the second class are those which deliver the drug in specific cells (e. g., tumor cells) of the targeted area without influence on normal cells;
③ Targeted preparations of the third class are those which act on a certain area in the cells.