[Distribution of acitretin in human skin]

Acitretin has recently been introduced for the systemic treatment of dermatologic diseases such as psoriasis and congenital disorders of keratinization. At present, only an oral form of this drug is available. However results from recent studies have shown that considerable drug concentrations can be delivered to the skin by topical administration of acitretin. Based on this data we addressed the question whether the topical administration of acitretin can produce in humans a drug concentration in the skin which exceeds the drug concentration that is found in the skin after multiple oral acitretin dosing and is reported to be clinical effective. Drug concentrations in the skin were investigated under conditions in which the maximum dose that can be administered in a therapeutic situation was applied. Additionally, three different skin sampling techniques, the punch biopsy, the shave biopsy and the suction blister technique were validated to quantitate acitretin in the skin. The drug concentrations in skin after systemic application in a steady state situation were comparable with the drug concentration reached after a single 24 hours topical application of a saturated acitretin/isopropylmyristate formulation. However, no unequivocal effects in psoriasis and disorders of keratinization were observed up to now by the topical administration of acitretin. The inverse drug concentration gradients which are present in the skin, depending on the route of administration, may explain differences in activity. The skin samples in our and other studies were homogenized or dissolved and thus much of the anatomical information is lost. The latter may be most important for the understanding of the local events.