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A spectrophotofluorometric method for the quantitative determination of hydrocortisone absorption in the skin from dermatological medications MacKenzie, Helen May

Abstract

The assessment of drug activity in skin is hampered by the lack of adequate methods for quantitative measurement of drug penetration in skin. Therefore, a new method was developed with the following features. The drug, hydrocortisone, chosen for its clinical and pharmaceutical importance, was applied under occlusive dressing for varying time intervals. Small skin samples, which ranged from 0.5 to 20 mg in size, were removed, in vivo, from humans or animals by a new dermatome serial slicing technique. The amount of hydrocortisone absorbed into the epidermis and/or dermis was determined by a new spectrophotofluorometric procedure, based on an older technique described for blood. The tissue levels were then correlated with simultaneously determined skin function measurements. The assay was done at 470 mμ and 525 mμ excitation and emission wavelengths, respectively. Hydrocortisone was extracted from homogenized tissue with dichloromethane. Fluorescence was developed with 85:15 w/w sulphuric acid - ethyl alcohol solution. Hydrocortisone was found in epidermis, but not in dermis. These results confirm current theories on hydrocortisone depot formation in the epidermis. Among the 14 patients examined, the concentration of hydrocortisone in epidermis varied greatly from 20 μg to 358 μg per Gm wet weight of tissue. Exploratory correlations between skin respiration rates, vasoconstriction, and the amount of hydrocortisone in epidermis have been done. The analytical reliability has been discussed.

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