title: Polymer blends used for the coating of multiparticulates: comparison of aqueous and organic coating techniques.
abstract: OBJECTIVE
  The purpose of this study was to use polymer blends for the coating of pellets and to study the effects of the type of coating technique (aqueous vs. organic) on drug release.
  
  
  METHODS
  Propranolol HCl-loaded pellets were coated with blends of a water-insoluble and an enteric polymer (ethyl cellulose and Eudragit L). Drug release from the pellets as well as the mechanical properties, water uptake, and dry weight loss behavior of thin polymeric films were determined in 0.1 M HCI and phosphate buffer, pH 7.4.
  
  
  RESULTS
  Drug release strongly depended on the type of coating technique. Interestingly, not only the slope, but also the shape of the release curves was affected, indicating changes in the underlying drug release mechanisms. The observed effects could be explained by the higher mobility of the macromolecules in organic solutions compared to aqueous dispersions, resulting in higher degrees of polymer-polymer interpenetration and, thus, tougher and less permeable film coatings. The physicochemical properties of the latter were of major importance for the control of drug release, which was governed by diffusion through the intact polymeric films and/or water-filled cracks.
  
  
  CONCLUSIONS
  The type of coating technique strongly affects the film microstructure and, thus, the release mechanism and rate from pellets coated with polymer blends.
authors.affiliation: College of Pharmacy, Freie Universitaet Berlin, 12169 Berlin, Germany.
authors.forename: Florence
authors.initials: F
authors.lastname: Lecomte
authors.forename: Juergen
authors.initials: J
authors.lastname: Siepmann
authors.forename: Mathias
authors.initials: M
authors.lastname: Walther
authors.forename: Ross J
authors.initials: RJ
authors.lastname: MacRae
authors.forename: Roland
authors.initials: R
authors.lastname: Bodmeier
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage; D002482:Cellulose / Q000031:analogs & derivatives*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004339:Drug Compounding; D005079:Excipients; D006244:Hardness; D007700:Kinetics; D009930:Organic Chemicals; D019999:Pharmaceutical Solutions; D011108:Polymers; D011109:Polymethacrylic Acids; D011433:Propranolol / Q000008:administration & dosage; D012995:Solubility; D013608:Tablets, Enteric-Coated / Q000737:chemistry*; D014867:Water
chemical_list: D000319:Adrenergic beta-Antagonists; D005079:Excipients; D009930:Organic Chemicals; D019999:Pharmaceutical Solutions; D011108:Polymers; D011109:Polymethacrylic Acids; D013608:Tablets, Enteric-Coated; D014867:Water; C038300:methylmethacrylate-methacrylic acid copolymer; C013517:ethyl cellulose; D002482:Cellulose; D011433:Propranolol