Application of the Minolta Chromameter to the Assessment of Corticosteroid-lnduced Skin Blanching

Abstract

Technological advances in both analytical methodology and statistical analysis have refined the science of bioequivalence testing. In recent years, the design, performance, and evaluation of bioequivalence studies have received much attention from the industry, academia, and, more recently, from regulatory agencies. The drug delivery field that has possibly received the least attention in this regard is the bioequivalence assessment of topical formulations. Corticosteroids, especially, have been evaluated for several decades using a visual grading system for subjectively recording the intensity of the drug-induced vasoconstriction. As an alternative, a number of researchers (Pershing et al., 1992; Waring et al., 1993; Clarys et al., 1995) have used a Minolta chromameter to assess skin color following the application of cortico-steroid-containing formulations. Some years ago the Food and Drug Administration (FDA) proposed that a chromameter be used to measure blanching intensity when assessing topical corticosteroid activity for bioequivalence purposes (FDA, 1995). With this instrument it is theoretically possible to measure the intensity of skin-blanching as an absolute color, based on the tristimulus analysis of a reflected xenon light pulse. The result is expressed as a three-dimensional coordinate consisting of two color coordinates (the green-red or a-scale and the yellow-blue or b-scale) and a luminance coordinate (black-white or L-scale). These three coordinates (a, b,and L) should define the absolute color of a skin site at each Observation time as the vasoconstriction phenomenon varies