Interaction of a lecithin microemulsion gel with human stratum corneum and its effect on transdermal transport

A soybean lecithin microemulsion gel has been studied as a possible matrix for transdermal drug delivery. This gel is transparent and viscous, and it is composed of soybean phosphatidylcholine (lecithin), isopropyl palmitate and a small amount of water. In vitro percutaneous penetration studies of two anti-inflammatory drugs, indomethacin and diclofenac, dissolved in the gel-system resulted in steady state fluxes of about 1 mu g h(-1) cm(-2). In order to estimate the function of the gel as a potential transdermal penetration enhancing system, interaction studies with isolated human stratum corneum were performed using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) as well as low-temperature scanning electron microscopy. These studies indicated that the lecithin gel, in particular isopropyl palmitate, affects the stratum corneum lipid organization even after 1-day incubation (FTIR, DSC), whereas recent in vivo human skin irritation tests showed no significant irritancy.