Use of a surface recovery technique to evaluate percutaneous absorption of 5-methoxypsoralen in humans

Abstract

In vivo percutaneous absorption experiments in humans are much more difficult to perform than either experiments in animal models or in vitro penetration studies. The majority of human in vivo percutaneous absorption experiments have used indirect radiochemical methods [2] or skin punch biopsy methods [11], which pose technical and ethical problems. However, some authors [7, 10] have described more acceptable techniques such as a surface recovery technique, which is completely non-invasive but hard to perform because it is difficult to remove 100% of the compounds from the skin immediately after their application. A surface disappearance technique has also been reported which uses very low radioactive doses, permitting residual radioactivity assessment on the skin [41. In this paper, a simple modified surface recovery technique is described to quantify 5-methoxypsoralen (5MOP) percutaneous absorption in humans after the application of a suntan product. This method involves applying accurately known quantities of a compound (in this study, 5-MOP in an emulsion) to several skin areas. Then, using petroleum ether, the unabsorbed product is completely removed at different times, and the difference between the applied and the recovered quantities corresponds to the quantity absorbed. High performance liquid chromatography (HPLC) was used to determine the quantities of unabsorbed 5-MOP on the skin surface. 5-MOP is derived from the essential oil of bergamot. It was formulated at a level of 29 rig/rag as a water-in-oil emulsion with the following composition: water 60%, petroleum jelly 7.5%, isopropyl myristate 6%, fatty acid ester i 0%, sun screens 5 %, glycerin 3 %, propylene glycol 1%, groundnut oil 3% and essential oil of bergamot, vitamin A, vitamin E and preservative to 100%.