Multinuclear NMR characterisation and dermal delivery of fluorinated drugs in soybean-microemulsion systems

The present study evaluated the effect of different commercially available soybean lecithins in microemulsion systems in terms of microstructure transformation, physicochemical properties and transport of selected entrapped fluorinated drugs through skin. Physicochemical characterisations by particle size and polydispersity index (PDI) measurements were performed and a direct correlation with NMR self-diffusion coefficients of the individual components was found. An increase of lysophosphatidylcholine (LPC), phosphatidylethanolamine (PE) and lysophosphatidylethanolamine (LPE) in the phospholipid mixtures increased the mean particle sizes and PDI. Bicontinous microemulsion structures were proven by 1H and 31P NMR in the placebo microemulsions. Reasonable permeation of the lipophilic drugs of all microemulsions systems was confirmed in standard diffusion studies using porcine skin. This could be due to the incorporation of the drugs in the surfactant structure of the lecithin based bicontinous micro textures, as proven by 19F NMR self-diffusion studies.