Abstract
Microencapsulation techniques, phase separation and solvent evaporation, have been developed for preparation of drug-containing monolithic microcapsules for prolonged release using poly(lactide-co-gtycolide) and copoly(lactic/glycolic) acid. A new technique encapsulating highly water-soluble drugs has been established by modifying the solvent evaporation method using a w/o/w emulsion. The method can completely entrap the highly water-soluble drugs into the microcapsules and can easily prepare the microcapsules in a large scale. The drug releases in a pseudozero order kinetics for several weeks with degradation of the polymers after an initial burst release. Many prolonged release-microcapsules containing water-soluble peptides and proteins were prepared by this method. It is difficult to avoid the initial burst release from the microcapsules containing a water-soluble drug, and a technique to avoid the burst has not been found yet. But an insulin-microcapsule system without the initial burst release has just been presented in the DDS meeting in Japan in this summer. The initial burst problem will be solved in near future.
