Biodegradable microspheres in drug delivery.

General aspects of biodegradable microspheres prepared from natural and synthesized polymers used in drug delivery systems are reviewed first from various viewpoints: characteristics of biodegradable polymers (physicochemical properties, bioerosion mechanism, biocompatibility), preparation method for the microspheres, drug release from parenteral products and briefly nonparenteral products. The relationship between release pattern and pharmacological activity of therapeutic peptides and proteins and rational controlled release design are also discussed. In the latter half, successful sustained release depot formulations of peptides, leuprorelin acetate, and thyrotropin-releasing hormone (TRH), utilizing poly(lactic acid) (PLA) and poly(lactic/glycolic acid) (PLGA) microspheres are reviewed with respect to preparation, drug release, biocompatibility, pharmacological effects, and results of clinical studies. Thereafter, studies on antitumor therapy by chemoembolization using PLGA microspheres containing an angiogenesis inhibitor (TNP-470) are described as an example of targeted drug delivery with biodegradable microspheres.