title: In vitro degradation study of polyester microspheres by a new HPLC method for monomer release determination.
abstract: Biodegradable polyesters have increasing importance as materials used for the preparation of microspheres. The knowledge of their degradation process is important to prepare microparticulate delivery systems with suitable drug release rates. In this work an in vitro degradation study of empty and drug loaded microspheres is described. Three different polyesters were used: two poly-d, l-lactides of different molecular weight and a poly-d, l-lactide-co-glycolide (50:50). Diazepam has been chosen as the model drug. Solvent evaporation and spray-drying were used as preparation methods. To study the polymer degradation process, a new HPLC method is proposed for the direct and (in the case of the copolymer) simultaneous determination of the monomer(s): lactic acid (LA) and glycolic acid (GA). SEM and particle size analysis highlight the different characteristics of the particles, depending on their preparation method: spray-dried spheres result to be always smaller with respect to particles obtained by solvent evaporation. The results obtained indicate in particular that: the preparation methods play an important role in determining the degradation behaviour of microspheres, as unloaded spray-dried particles are characterized by a higher monomer release rate with respect to microspheres obtained by solvent evaporation; PLGA spheres degrade faster than PDLLA microparticles, according to the higher hydrophilicity of the copolymer; the two monomers are released at a different rate in the case of PLGA (faster for GA, slower for LA); the presence of diazepam increases the polymer degradation rate, with respect to empty particles.
authors.affiliation: Dipartimento Chimica Farmaceutica, via Taramelli 12, Università di Pavia, Pavia, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Giunchedi
authors.forename: B
authors.initials: B
authors.lastname: Conti
authors.forename: S
authors.initials: S
authors.lastname: Scalia
authors.forename: U
authors.initials: U
authors.lastname: Conte
mesh_terms: D001672:Biocompatible Materials / Q000008:administration & dosage / Q000737:chemistry*; D002626:Chemistry, Pharmaceutical; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003692:Delayed-Action Preparations; D003975:Diazepam / Q000008:administration & dosage / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000737:chemistry*; D008863:Microspheres; D010316:Particle Size; D011091:Polyesters / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D003692:Delayed-Action Preparations; D011091:Polyesters; D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; C033616:poly(lactide); D003975:Diazepam