Therapeutic applications of prolonged controlled release parenteral microcapsule systems using biodegradable polymer were discussed. The microcapsule system has advantages as follows : the system can be easily injected with a suspending vehicle and a conventional syringe ; it is not necessary to take the system out of the injection site after the release of all the drug, permitting this system to be injected into the same site chronically ; in many cases, smaller doses than those required in the cases of injecting aqueous solutions are expected to be sufficient with increased pharmacological effects when its system is used. Recently, applications for a highly potent LHRH agonist were reported. The system consisted of a biodegradable polymer, copoly (lactic/glycolic) acid (PLGA), containing a highly potent LHRH agonist termed leuprolide acetate released the drug for one month at a pseudo zero order kinetics. The microcapsules were applied clinically for treatment of prostate cancer, resulting remarkably that the microcapsules effectively reduced the dose of the drug required to up to one-fourth of that needed when an aqueous solution is injected daily. This system provides an ideal delivery of water soluble peptide hormone. Further, limits of this system to apply a drug are discussed.
