title: Microemulsion microstructure influences the skin delivery of an hydrophilic drug.
abstract: OBJECTIVE
  We aimed to investigate the influence of microemulsion nanoscale organization as either oil-in-water droplets, water-in-oil droplets, or bicontinuous structures on skin delivery of drugs assisted by microemulsions.
  
  
  METHODS
  Three microemulsions of different microstructure, o/w, w/o, and bicontinuous at the skin temperature (32°C), having the same oil and water contents and containing the same ingredients were selected using the Kahlweit fish phase diagrams method. The microemulsions are quaternary mixtures of the Polysorbate 21 (Tween®21) and Sorbitan monolaurate (Span®20) surfactants, isononyl isononanoate oil and water. The microemulsion nanostructure was characterized by electrical conductivity, Pulsed Field Gradient Spin-Echo NMR and Small-Angle Neutron Scattering measurements. The Franz cell method was used to monitor skin absorption of caffeine loaded in microemulsions over 24 h exposure to excised pig skin.
  
  
  RESULTS
  Three microemulsions with the three structures were selected, keeping the same composition but the Tween®21/Span®20 ratio. The transdermal flux of caffeine was in the order aqueous solution ≈ w/o < bicontinuous < o/w microemulsion. The o/w microemulsion allows the permeation of 50% of the applied dose within 24 h.
  
  
  CONCLUSIONS
  The structure of microemulsions is of relevance for skin absorption. The water-continuous structures allow faster transport of hydrophilic drugs.
authors: Université de Lyon Laboratoire d'Automatique et de Génie des Procédés (LAGEP) UMR CNRS 5007, Institut des Sciences Pharmaceutiques et Biologiques Laboratoire de Dermopharmacie et Cosmétologie, Université Lyon 1, Villeurbanne, France.
authors: Wafa
authors: W
authors: Naoui
authors: Marie-Alexandrine
authors: MA
authors: Bolzinger
authors: Bernard
authors: B
authors: Fenet
authors: Jocelyne
authors: J
authors: Pelletier
authors: Jean-Pierre
authors: JP
authors: Valour
authors: Rafik
authors: R
authors: Kalfat
authors: Yves
authors: Y
authors: Chevalier
mesh_terms: D000279:Administration, Cutaneous; D000818:Animals; D002110:Caffeine / Q000737:chemistry / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid; D016503:Drug Delivery Systems; D004655:Emulsions / Q000737:chemistry / Q000493:pharmacokinetics; D057927:Hydrophobic and Hydrophilic Interactions; D009682:Magnetic Resonance Spectroscopy; D008832:Microchemistry; D009821:Oils / Q000737:chemistry; D012867:Skin / Q000737:chemistry*; D013552:Swine; D014867:Water / Q000737:chemistry
chemical_list: D004655:Emulsions; D009821:Oils; D014867:Water; D002110:Caffeine