title: A rheological method to evaluate the physical stability of highly viscous pharmaceutical oil-in-water emulsions.
abstract: OBJECTIVE
  The aim of this study was to develop a rheological method to evaluate the stability of highly viscous pharmaceutical emulsions. Thereby, the time devoted to the storage tests could be reduced and manufacturers could save time in optimizing their formulations and manufacturing techniques for topical pharmaceutical forms. The influence of the type of oil and the type of emulsifier on the microstructure of the emulsions was also studied.
  
  
  METHODS
  The samples were stored at 25 and at 50 degrees C for 6 months and analysed every month using rheological as well as microscopic techniques. The size and the organization of the droplets within the emulsion were determined by freeze-fracture electron microscopy and optical contrast phase microscopy.
  
  
  RESULTS
  A decrease in the rheological parameters was observed for the OC emulsions ("Tween/Span" emulsions made with olive oil) and the "Montanov" emulsions. The rheological measurements showed that the structure of the OC emulsions and that of the emulsions made with the Montanov 82 emulsifier become more brittle when submitted to a shear force. The micrographs obtained by freeze-fracture electron microscopy showed that for OC only the oil droplets arrange in a network structure. Storage tests at 50 degrees C confirmed the rheological assumptions on the stability of emulsions.
  
  
  CONCLUSIONS
  The study of the effect of shearing on the emulsions allowed quick discrimination between the emulsions according to their stabilities. The rheological tool gave information on the structure of the emulsions and on the aging process.
authors.affiliation: Lab. GOAE, CNRS UMR 6171, service 451, Université Paul Cézanne Aix-Marseille III, Avenue Escadrille Normandie Niemen 13397, Marseille cedex 20, France. houdamas@yahoo.fr
authors.forename: Houda
authors.initials: H
authors.lastname: Masmoudi
authors.forename: Philippe
authors.initials: P
authors.lastname: Piccerelle
authors.forename: Yveline
authors.initials: Y
authors.lastname: Le Dréau
authors.forename: Jacky
authors.initials: J
authors.lastname: Kister
mesh_terms: D000287:Administration, Topical; D000465:Algorithms; D004355:Drug Stability; D004356:Drug Storage; D004655:Emulsions / Q000737:chemistry*; D005079:Excipients / Q000737:chemistry; D005614:Freeze Fracturing; D006863:Hydrogen-Ion Concentration; D008854:Microscopy, Electron; D008858:Microscopy, Phase-Contrast; D009821:Oils; D010316:Particle Size; D011136:Polysorbates / Q000737:chemistry; D012212:Rheology / Q000379:methods*; D013501:Surface-Active Agents / Q000737:chemistry; D014783:Viscosity; D014867:Water
chemical_list: D004655:Emulsions; D005079:Excipients; D009821:Oils; D011136:Polysorbates; D013501:Surface-Active Agents; D014867:Water