title: Two- and three-layer tablet drug delivery systems for oral sustained release of soluble and poorly soluble drugs.
abstract: BACKGROUND
  Multilayer tablets are gaining importance in oral sustained drug delivery. They consist of an active matrix core and one or more layers applied during tableting which may act as barriers and regulate drug release.
  
  
  OBJECTIVE
  To examine the release performance of two model drugs, diclofenac sodium and furosemide, from two- and three-layer drug delivery systems using as carriers hydrophilic swellable polymers, namely, Metolose, Polyox, Xantham gum, and an erodible material Gantrez.
  
  
  CONCLUSIONS
  All prepared formulations demonstrated sustained release profiles. They also indicated that the carrier characteristics (particularly swelling-expansion, erosion-dissolution) and drug solubility in combination with tablet structure considerably influenced the performance of examined formulations as well as their mode and mechanisms of release. In general our findings show that the differences in drug release between the two- and three-layer tablets are small as it appears that two-layer tablets exhibit a slightly higher release. Because of its greater erosion Gantrez formulations displayed faster release relative to Xantham gum, as did Metolose formulations compared to Polyox formulations. A faster release rate was also noted with diclofenac formulations compared to those of furosemide because of diclofenac's higher solubility mainly seen at early time period.
  
  
  CONCLUSIONS
  All three-layer Gantrez tablets containing either diclofenac or furosemide and the two-layer furosemide formulation demonstrated a biphasic release. The above indicate that both structures may be used successfully for sustained release drug delivery. In addition the use of multilayer tablets, consisting of materials with suitable properties, may result in modulation of drug release.
authors.affiliation: Faculty of Pharmacy, Department of Pharmaceutical Technology, University of Athens, Athens, Greece. efentakis@pharm.uoa.gr
authors.forename: M
authors.initials: M
authors.lastname: Efentakis
authors.forename: H
authors.initials: H
authors.lastname: Naseef
authors.forename: M
authors.initials: M
authors.lastname: Vlachou
mesh_terms: D000284:Administration, Oral; D003692:Delayed-Action Preparations / Q000008:administration & dosage / Q000032:analysis / Q000737:chemistry; D004008:Diclofenac / Q000008:administration & dosage* / Q000032:analysis / Q000737:chemistry*; D004058:Diffusion; D004337:Drug Carriers / Q000008:administration & dosage* / Q000032:analysis / Q000737:chemistry*; D004339:Drug Compounding / Q000379:methods; D016503:Drug Delivery Systems; D005665:Furosemide / Q000008:administration & dosage* / Q000032:analysis / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D011108:Polymers / Q000737:chemistry; D012995:Solubility; D013607:Tablets; D014867:Water / Q000032:analysis
chemical_list: D003692:Delayed-Action Preparations; D004337:Drug Carriers; D011108:Polymers; D013607:Tablets; D014867:Water; D004008:Diclofenac; D005665:Furosemide