Percutaneous absorption of dexamethasone estimated by a plasma radioimmunoassay

Precutaneous absorption of dexamethasone and its effect on the pituitary adrenal axis were measured in vivo in normal human subjects after application to skin. Specific plasma dexamethasone and cortisol radioimmunoassays were used. Following application of 1% dexamethasone on 500 cm2 of normal skin, the plasma dexamethasone concentration was maximal at 2 hr, and the average absorption was 0.25% over 8 hr; significant cortisol suppression occurred at 2, 4, and 8 hr. This technique: (1) provides an accurate assessment of the in vivo absorption of dexamethasone applied to human skin, (2) avoids exposure of the subjects to radioactive steroids, (3)permits estimation of the quantity of unmetabolized steroids absorbed, and (4) serves as a possible model for the development of similar assays for other topical steroids.