PERCUTANEOUS ABSORPTION OF ADRENAL STEROIDS 147 It is the purpose of this paper to review the studies which have been carried out to date on the subject of the percutaneous absorption of adrenal steroids, and then to outline briefly some further pathways for future investigation. HISTORICAL ACCOUNT Or STUDIES ON THE ABSORPTION OF ADRENAL STEROIDS BY THE SKIN HYDROCORTISONE The earliest attempts to demonstrate the percutaneous absorption of hydrocortisone were based either on the search for physiological effects known to be produced by systemic administration of the hormone or on the possible demonstration of an increase in hydrocortisone metabolites in plasma or urine. Castor and Baker (9) observed that daily topical applications of an alcoholic solution of hydrocortisone to the skin of rats induced profound atrophic changes. After two to three months marked thinning of the epidermis and dermis and a decrease in the size of sebaceous glands were found histologically. Complete inhibition of hair growth in the treated areas was also noted. Since previous investigations had shown that parenteral ACTH produced analogous changes in the skin of rats (10), it was presumed that the findings following topical application of hydro- cordsone were the result of direct tissue effects from the absorbed hor- mone. Smith (11) performed circulating eosinophile counts on eight normal adults and seven patients with generalized skin disease four hours after a single ten-minute inunction of an ointment containing 150 mgm. of hydro- cordsone acetate. For both the volunteer subjects and the patients no consistent alterations in the eosinophile counts were found after the inunction of hydrocortisone ointment as compared with baseline counts recorded prior to application. Witten, et al. (12) working with six normal adult volunteers and nine patients with generalized dermai:oses, applied a total of 750 mgm. of hydrocortisone acetate in an ointment vehicle to large areas of the skin surface of each individual over a three-day period. Using the colorimetric method of Silber and Porter (13) these workers found no significant altera- tion in pre-inunction and post-inunction levels of 17, 2!-dihydroxy-20 ketosteroids in the blood or urine of any of the subjects tested. In another study reported by Fitzpatrick, et al. (14) 17.5 gins. of hydro- cordsone acetate in a lotion vehicle were applied to the skin of each of two patients with generalized atopic dermatitis over a se•en-day period. In neither subject could an increase in urinary excretion of hydrocortisone be demonstrated. With the completion of these studies it became evident that for humans

148 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS there was little danger from the absorption and consequent systemic effects of topical hydrocortisone in the usual concentrations (1 to 2.5 per cent), even when the steroid was applied to large areas of altered skin over long periods of time. Consequently, the chief point of interest now shifted to a consideration of methods capable of demonstrating the percutaneous ab- sorption of minute quantities of the hormone. Indirect evidence for the percutaneous absorption of hydrocortisone in human subjects was provided by the observation of Lerner and Takahashi (14) that topical administration of the hormone suppressed excessive uri- nary excretion of melanocyte stimulating hormone (MSH). This reduc- tion in urinary levels was presumed to follow pituitary inhibition by hydro- cortisone. Two patients with high urinary output of MSH applied 30.0 cc. of 2.5 per cent hydrocortisone acetate lotion to normal skin sites on the arms each day. After one week urinary MSH excretion fell to normal levels. Output of urinary MSH increased again when the lotion applica- tions were discontinued. By ascertaining the amount of orally adminis- tered hydrocortisone required to reduce urinary MSH excretion to normal levels in these subjects Lerner and Takahashi estimated that at least 3 per cent of the locally applied hydrocortisone was absorbed from the skin. The first direct demonstration of hydrocortisone absorption through human skin was carried out when hydrocortisone-4-O 4 free alcohol became available for investigative use. After Hellman and his co-workers (15) showed that 70-80 per cent of hydrocortisone-4-C •4 given intravenously to human subjects appeared in the urine within the first twenty-four hours, we tested the percutaneous absorption of hydrocortisone by applying the same labeled steroid to normal human skin and examining the 17-keto- steroid fraction of the urine for radioactivity (t6). The labeled steroid, with an added amount of nonradioactive "carrier" hydrocortisone, was incorporated into an ointment base which was then applied to normal skin sites on the forearm of two adult volunteers. These test sites were pro- tected throughout by perforated aluminum eye patches taped firmly to the skin. Twenty-four-hour urine specimens were collected daily over a six-day period and the 17-ketosteroid fraction was isolated by the tech- nique of acid hydrolysis. Significant radioactivity was detected in this urine fraction within twenty-four hours after application. The peak excretion of hydrocortisone occurred during the second twenty-four hours, but lower levels of radioactivity persisted throughout the six-day experi- mental period. Tetrahydro-hydrocortisone, the chief urinary metab- olite of hydrocortisone, was isolated from urine subjected to enzy- matic hydrolysis with •-glucuronidase. Although the method used was not suitable for precise quantitative estimations, the results of this study indicated that less than 1 per cent of the hydrocortisone applied to the skin was absorbed.