| Popis: |
The major criticism of the human bioassay currently employed for corticosteroid activity is that it requires the use of experienced assessors subjectively to determine and rank the degree of skin pallor (blanching) induced in the skin by the topical application of a formulated product. 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 blanching activity. The aim of the present study was to evaluate further the possibility of employing the Chromameter routinely in the bioassay of topical corticosteroids. In one study, employing ten volunteers, the effects of pressure of the measuring device on the skin and the influence of site of application were determined, prior to the application of any active agent. Blanching profiles were determined for clobetasol propionate (0.05%) and betamethasone 0.1% (as valerate) creams under occluded and unoccluded conditions (in a further two studies, each comprising 10 volunteers) using both visual assessment and instrumental measurement. It was established that: (1) application of pressure to the skin induces a measurable change in skin colour and must be avoided 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 diurnal variation in skin colour is subtracted from the readings obtained as a result of corticosteroid-induced blanching, then a good correlation exists between the visual and Chromameter techniques both for very potent and potent corticosteroids. On the basis of these results, it is 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. |
