An Assessment of In Vitro Permeation Testing Finite Dose Methodology

Pharmaceutical emulsifiers used in topical products are either non-ionic surfactants or anionic surfactants. Non-ionic emulsifiers are preferred because they minimally extract epidermal lipids from the stratum corneum (SC) and are well tolerated when applied topically. During topical vehicle development, the Franz diffusion cell allows investigators to determine the amount of drug delivered across the SC after topical application. In this study, we characterized extraction and permeation of 10 naturally occurring SC lipids in excised human skin loaded on a Franz cell 24 h after treatment with 4% sodium lauryl sulfate (SLS) aqueous solution versus neat water. Dermatomed human skin was loaded onto vertical Franz cells and chambers were filled with 0.9% NaCl solution. A 7.5-µL dose of water or 4% SLS aqueous solution was added to each Franz cell. Samples were tape stripped, collected, combined, and extracted with 2.0 mL of 1-hexanol/isopropanol/isopropyl myristate/N-methyl-2-pyrrolidone (15/25/20/40 by volume) overnight at 32°C on an orbit shaker. All 10 lipids were recovered from skin in sufficient amounts to be quantitated by liquid chromatography tandem mass spectrometry. Similar amounts of epidermal lipids were extracted from dermis, epidermis, and SC 24 h after dosing with water or 4% SLS, despite varying demographics of the three donors. For the 10 SC lipids characterized in this study, only ceramides showed lag times for appearing in receptor solution of the Franz cells. This study showed that ceramide NP and NS are suitable markers for epidermal lipid extraction after in vitro permeation testing using finite dosing of dermatomed human skin.