In the field of dermal drug delivery, determining the penetration depth of actives is a standard procedure for the development of novel formulations. Regarding the vehicle components, respective penetration studies are rather scarce due to their often challenging analytics. However, an understanding of the interactions between drugs and additives during skin penetrating could help to develop promising drug delivery systems. Thus, the objective of the present study was to simultaneously monitor the skin penetration of the incorporated model drug diclofenac sodium and the semifluorinated oil perfluorohexyloctane (F6H8) from newly developed nanoemulsions. In vitro tape stripping studies were conducted and the tapes were analysed for their content of drug and additive in parallel by HPLC and 19F NMR. The penetration depth and total recovered amount of both substances of interest were successfully determined on each tape strip. The vehicle oil compound F6H8 itself showed a very small skin penetration, while the penetration of diclofenac sodium was consistently about 9- to 10-fold higher. Higher amounts of the oil content led to higher skin penetration of diclofenac sodium and slightly increased oil penetration; this effect might be explained by the increasing occlusion effect caused by increasing amounts of fluorinated oil.
Keywords: (19)F NMR; Diclofenac sodium; Nanoemulsion; Semifluorinated alkane; Skin penetration; Tape stripping.
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