title: Quantitative vasoconstrictor assay for topical corticosteroids: the puzzling case of fluocinolone acetonide.
abstract: BACKGROUND
  The validity of the vasoconstrictor test has been questioned because of the apparent nonequivalence of some generic corticosteroid products.
  
  
  OBJECTIVE
  Our purpose was to determine the vasoconstrictor activity of a generic 0.025% fluocinolone acetonide ointment by two different methods, dilution by volume and dilution by area of application.
  
  
  METHODS
  Vasoconstrictor activity on a visual 4-point scale was measured in 20 volunteers. Topical fluocinolone acetonide ointment (0.025%) was tested by comparing dilution by volume (1:1, 1:3, and 1:7) in petrolatum and dilution by area of application. Fluocinolone release from the diluted ointments was also measured with an in vitro method.
  
  
  RESULTS
  Dilution by area gave the expected results, a decreasing average vasoconstrictor score; but dilution by volume did not. Both the 1:1 and 1:3 dilutions inexplicably showed greater activity than the full-strength product; this finding was similarly reflected in the in vitro studies that showed a greater rate of drug release from the 1:1 and 1:3 dilutions.
  
  
  CONCLUSIONS
  Dilution by area provides a useful quantitative assay for comparative vasoconstrictor activity.
authors.affiliation: Department of Dermatology, University of Arkansas for Medical Sciences, Little Rock.
authors.forename: J D
authors.initials: JD
authors.lastname: Guin
authors.forename: M S
authors.initials: MS
authors.lastname: Wallis
authors.forename: R
authors.initials: R
authors.lastname: Walls
authors.forename: P A
authors.initials: PA
authors.lastname: Lehman
authors.forename: T J
authors.initials: TJ
authors.lastname: Franz
mesh_terms: D000328:Adult; D001415:Back; D002626:Chemistry, Pharmaceutical; D002851:Chromatography, High Pressure Liquid; D016568:Drugs, Generic / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D005260:Female; D005446:Fluocinolone Acetonide / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology; D005542:Forearm; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D013810:Therapeutic Equivalency; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D016568:Drugs, Generic; D005446:Fluocinolone Acetonide; C035394:fluocinolone