Variability and correlation of chromameter and tape-stripping methods with the visual skin blanching assay in the quantitative assessment of topical 0.05% betamethasone dipropionate bioavailability in humans

Abstract

Bioavailability between five commercial 0.05% betamethasone diproprionate formulations in human skin is demonstrated with three methods; visual skin blanching, tape-stripping and a chromameter. Reproducibility of each method is evaluated for both intra- and inter-subject variability. The variability (coefficient of variation) in the intra-subject studies is consistently less than that in the inter-subject studies for all methods evaluated. The variability in the subjective visual skin blanching assay increases as a function of time. Variability in the tape-stripping technique performed at one time point only ranges from 7 to 30% in the intra-subject study to greater than 70% in the inter-subject study. Variability in the a scale on the chromamater is consistent over time (approx. 24%). The b scale on the chromameter demonstrates an inter-subject variation of about 15%, while the luminosity scale demonstrates a variability of approx. 6%. The rank order of 0.05% betamethasone diproprionate formulation potency is similar between the visual skin blanching assay, tape-stripping and the a scale on the chromameter. Further, the rank correlation between tape-stripping and the a scale on the chromameter with the subjective visual skin blanching assay is moderate to excellent ( r=0.6, and −0.9, respectively). Thus, tape-stripping and the chromameter offer the investigator two objective, standardized and noninvasive methods with which to compare bioequivalence of topical corticosteroids.