ASSESSMENT OF CORTICOSTEROID-INDUCED SKIN BLANCHING - EVALUATION OF THE MINOLTA CHROMAMETER CR200

The major criticism of the human bioassay currently employed for corti costeroid activity is that it requires the use of experienced assessor s subjectively to determine and rank the degree of skin pallor (blanch ing) induced in the skin by the topical application of a formulated pr oduct. Recently a number of studies have suggested that the use of tri -stimulus colorimetry (using the Minolta Chromameter CR 200) provides an instrumental and hence objective means of assessing such topical bl anching activity. The aim of the present study was to evaluate further the possibility of employing the Chromameter routinely in the bioassa y of topical corticosteroids. In one study, employing ten volunteers, the effects of pressure of the measuring device on the skin and the in fluence of site of application were determined, prior to the applicati on of any active agent. Blanching profiles were determined for clobeta sol propionate (0.05%) and betamethasone 0.1% (as valerate) creams und er occluded and unoccluded conditions (in a further two studies, each comprising 10 volunteers) using both visual assessment and instrumenta l measurement. It was established that: (1) application of pressure to the skin induces a measurable change in skin colour and must be avoid ed to prevent error in instrumental readings, (2) there is a variation in natural skin colour from elbow to wrist, (3) there is a marked but reproducible diurnal variation in skin colour, (4) providing the diur nal variation in skin colour is subtracted from the readings obtained as a result of corticosteroid-induced blanching, then a good correlati on exists between the visual and chromameter techniques both for very potent and potent corticosteroids. On the basis of these results, it i s recommended that the use of the Chromameter in skin-blanching assays still requires careful development and more validation before its use can be recommended in a bioassay intended to replace the traditional visual assessment method.