Quantitative vasoconstrictor assay for topical corticosteroids: the puzzling case of fluocinolone acetonide.
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.
Guin
J D
JD
Department of Dermatology, University of Arkansas for Medical Sciences, Little Rock.
Wallis
M S
MS
Walls
R
R
Lehman
P A
PA
Franz
T J
TJ
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*
D016568:Drugs, Generic; D005446:Fluocinolone Acetonide; C035394:fluocinolone