Monoacyl-phospatidylcholine based drug delivery systems for lipophilic drugs: Nanostructured lipid carriers vs. nano-sized emulsions

Monoacyl-phosphatidylcholine (MAPL) offers beneficial properties as surfactant for production of nanostructured lipid carriers (NLC). A MAPL-based NLC system was modified to evaluate the effect of different formulation parameters on the skin permeation and penetration of the incorporated lipophilic model drugs flufenamic acid and fludrocortisone acetate. Increased viscosity and increased MAPL content were investigated regarding their effect on formulation properties, physico-chemical long-term stability and skin permeation. In addition, a MAPL-based oil-in-water nano-sized emulsion was developed for the first time and investigated for comparison. Results showed high storage stability of both NLC and emulsions based on surfactant mixtures with 65% w/w of MAPL; mean particle sizes and zeta potential values remained stable over 16 weeks. Diffusion cell and in vitro tape stripping studies on porcine skin showed that these NLC systems were superior to the corresponding nano-sized emulsions in terms of skin permeation. Neither increased viscosity nor higher MAPL content proved to be an additional benefit for skin permeation of the model drugs. In conclusion, MAPL-based NLC are an interesting carrier system for lipophilic drugs irrespective of the system's viscosity and superior to corresponding nanoemulsions.