title: Characterization and stability study of a water-in-oil microemulsion incorporating quercetin.
abstract: BACKGROUND
  The effectiveness of a water/oil (w/o) microemulsion containing quercetin against ultraviolet B radiation (UVB) induced damage was recently demonstrated by our group. However, during the development of new pharmaceutical products, the evaluation of percutaneous absorption and in vivo effectiveness should be accompanied by evaluation of stability parameters as an integral part of the process.
  
  
  OBJECTIVE
  The aim was to investigate the stability of the final microemulsion formulation considering the temperature ranges of storage and application.
  
  
  METHODS
  The physical, chemical, and functional stability of this formulation under different conditions of storage during 12 months and the photostability of quercetin incorporated into this system over UVB exposure for 7 days were evaluated.
  
  
  RESULTS
  Although the results indicated a notable physical stability of the w/o microemulsions during the experimental period under all employed conditions, in both, the chemical and functional studies, a significant loss of quercetin content and antioxidant activity was found after 6 months of storage at 30°C/70% relative humidity and after 2 months at 40°C/70% relative humidity. The photostability study results demonstrated that the incorporation of quercetin into the w/o microemulsion maintained the previously demonstrated photostability of this flavonoid under forced exposure to UVB irradiation.
  
  
  CONCLUSIONS
  Thus, this work demonstrates that special storage conditions (at 4 ± 2°C) are necessary to maintain the functionality of the w/o microemulsion containing quercetin and mainly emphasizes the importance of studying physical, chemical, and functional parameters at the same time during stability evaluation of active principles.
authors.affiliation: Department of Pharmaceutical Science, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Fabiana T M C
authors.initials: FT
authors.lastname: Vicentini
authors.forename: Mirela M O L L
authors.initials: MM
authors.lastname: Vaz
authors.forename: Yris M
authors.initials: YM
authors.lastname: Fonseca
authors.forename: M Vitória L B
authors.initials: MV
authors.lastname: Bentley
authors.forename: Maria J V
authors.initials: MJ
authors.lastname: Fonseca
mesh_terms: D000975:Antioxidants / Q000737:chemistry* / Q000494:pharmacology; D002626:Chemistry, Pharmaceutical; D004304:Dosage Forms; D004355:Drug Stability; D004356:Drug Storage; D004655:Emulsions / Q000737:chemistry / Q000528:radiation effects; D006813:Humidity; D009821:Oils / Q000737:chemistry*; D010316:Particle Size; D011794:Quercetin / Q000737:chemistry* / Q000494:pharmacology; D013696:Temperature; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D004304:Dosage Forms; D004655:Emulsions; D009821:Oils; D014867:Water; D011794:Quercetin