Correlation between the drug penetration and the blanching effect of topically applied hydrocortisone creams in human beings

Two topical formulations of 2.5% hydrocortisone were tested to investigate the possible correlation between the blanching response of topically applied hydrocortisone and its release from the formulation after its penetration into the stratum corneum. After application of the cream, the stratum corneum was removed at different intervals and the hydrocortisone content was measured by radioimmunoassay. The blanching responses (expressed as mean score vs time) showed a 1.5-fold difference (significant at p = 0.0026) between the two creams at the maximum effect, which was reached for both creams after 16 hours. The amounts of hydrocortisone present in the stratum corneum after every application period showed a twofold difference (p = 0.0001) between the two creams. However, in contrast to the blanching, these quantities remained constant from 4 to 24 hours. This steady state characteristic may be partially due to the use of occlusion and to the excess formulation remaining at the surface. Although there is no parallelism with time between the results of the two methods, both give clear evidence of a difference in stratum corneum penetration and pharmacologic activity of the two formulations. Drug penetrations and pharmacodynamic activities of the two creams can be correlated with in vitro release characteristics.