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Nanostrucured lipid carriers (NLC) exhibit high skin targeting efficiency and good safety.They are promising vehicles for topical drug delivery.This study aims to compare the impact of particle size and drug loading on skin targeting efficiency of podophyllotoxin-loaded NLCs.Podophyllotoxin-loaded NLCs with small mean particle size (POD-NLC-Size) or high loading (POD-NLC-Loading) were prepared.Their skin targeting efficiencies were compared.To visualize skin distribution, POD was replaced with Nile red (NR).Skin distribution of NR-NLC-Size, NR-NLC-Loading was investigated using confocal laser scanning microscopy (CLSM).Skin irritation assessment of POD-NLC-Size was conducted.POD-NLC-Size and POD-NLC-Loading exhibit small particle size or high POD loading, respectively.Higher in vitro and in vivo rat skin deposits of POD (p< 0.01) were obtained by POD-NLC-Size, indicating that mean particle size affects NLC skin targeting efficiency more than drug loading.Examination of rat skin by CLSM shows that NR is primarily deposited in the epidermal layer by both NLCs.Rat skin treated with NR-NLC-Size clearly exhibits higher fluorescent intensity than that of NR-NLC-Loading, again indicating that mean particle size is a more important factor affecting skin targeting efficiency than drug loading.Skin irritation was not observed in intact or damaged rabbit skin treated with POD-NLC-Size, suggesting it is safe for topical use.Conclusion: NLC characteristics are consistent with good safety and high targeting specificity, when used topically.NLC skin targeting efficiency is affected more by mean particle size than drug loading.