The human skin blanching assay for in vivo topical corticosteroid assessment: II. Subject- and observer-dependent variation in blanching responses

Abstract

The human skin blanching (vasoconstriction) assay for the assessment of 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 observers are used in the bioassay to counteract the subjectiveness of the methodology. Given the inherent biological variability of the population, the minimum number of volunteers and observers required to give valid results in this assay has not been firmly established. This investigation consisted of three identical trials performed at 8 week intervals, utilising the same 18 volunteers and the same three observers in an attempt to address the question of intra- and inter-volunteer and observer reproducibility of the results from three replicate experiments. The results indicate that for any assay utilising this methodology, the number of application sites for a topical corticosteroid formulation 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 than two.