THE HUMAN SKIN BLANCHING ASSAY FOR IN-VIVO TOPICAL CORTICOSTEROID ASSESSMENT .2. SUBJECT-DEPENDENT AND OBSERVER-DEPENDENT VARIATION IN BLANCHING RESPONSES

The human skin blanching (vasoconstriction) assay for the assessment o f topical corticosteroids uses the skin pallor induced at the site of application as an indicator of the potency of the drug or efficacy of the delivery vehicle. Usually several volunteers and several visual ob servers are used in the bioassay to counteract the subjectiveness of t he methodology. Given the inherent biological variability of the popul ation, the minimum number of volunteers and observers required to give valid results in this assay has not been firmly established. This inv estigation consisted of three identical trials performed at 8 week int ervals, utilising the same 18 volunteers and the same three observers in an attempt to address the question of intra- and inter-volunteer an d observer reproducibility of the-results from three replicate experim ents. The results indicate that for any assay utilising this methodolo gy, the number of application sites for a topical corticosteroid formu lation should be at least 48, the number of volunteers (of either sex) should be not less than nine and the number of observers not less tha n two. (C) 1997 Elsevier Science B.V.