title: Importance of single or blended polymer types for controlled in vitro release and plasma levels of a somatostatin analogue entrapped in PLA/PLGA microspheres.
abstract: The aim of the work was to develop biodegradable microspheres for controlled delivery of the somatostatin analogue vapreotide and maintenance of sustained plasma levels over 2-4 weeks after a single injection in rats. Vapreotide was microencapsulated into end-group capped and uncapped low molecular weight poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA) by spray-drying and coacervation. Microspheres were prepared from single and blended (1:1) polymer types. The microparticles were characterized for peptide loading, in vitro release and pharmocokinetics in rats. Spray-drying and coacervation produced microspheres in the size range of 1-15 and 10-70 microm, respectively, and with encapsulation efficiencies varying between 46% and 87%. In vitro release of vapreotide followed a regular pattern and lasted more than 4 weeks, time at which 40-80% of the total dose were released. Microspheres made of 14-kDa end-group uncapped PLGA50:50 or 1:1 blends of this polymer with 35 kDa end-group uncapped PLGA50:50 gave the best release profiles and yielded the most sustained plasma levels above a pre-defined 1 ng/ml over approximately 14 days. In vitro/in vivo correlation analyses showed for several microsphere formulations a linear correlation between the mean residence time in vivo and the mean dissolution time (r=0.958) and also between the amount released between 6 h and 14 days and the AUC(6h-14d) (r=0.932). For several other parameters or time periods, no in vitro/in vivo correlation was found. This study demonstrates that controlled release of the vapreotide is possible in vivo for a duration of a least 2 weeks when administered i.m. to rats. These results constitute a step forward towards a twice-a-month or once-a-month microsphere-formulation for the treatment of acromegaly and neuroendocrine tumors.
authors.affiliation: Servicio de Farmacología Clínica, Clínica Universitaria, 31080 Pamplona, Spain. mjblanco@unav.es
authors.forename: María J
authors.initials: MJ
authors.lastname: Blanco-Príeto
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Campanero
authors.forename: Kamel
authors.initials: K
authors.lastname: Besseghir
authors.forename: F
authors.initials: F
authors.lastname: Heimgatner
authors.forename: Bruno
authors.initials: B
authors.lastname: Gander
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000737:chemistry / Q000493:pharmacokinetics; D019540:Area Under Curve; D001672:Biocompatible Materials; D003692:Delayed-Action Preparations; D004339:Drug Compounding; D005079:Excipients; D019344:Lactic Acid; D008297:Male; D008863:Microspheres; D010316:Particle Size; D011091:Polyesters; D011100:Polyglycolic Acid; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012995:Solubility; D012997:Solvents; D013004:Somatostatin / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics*
chemical_list: D000970:Antineoplastic Agents; D001672:Biocompatible Materials; D003692:Delayed-Action Preparations; D005079:Excipients; D011091:Polyesters; D011108:Polymers; D012997:Solvents; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; C051458:vapreotide; D019344:Lactic Acid; C033616:poly(lactide); D013004:Somatostatin