Investigation of plaunoi-loaded micro/nanoemulsions for the treatment of dermatitis: formulation, évaluation and skin irritation studies

The main objective of this work was to formulate microemulsions and nanoemulsions as delivery vehicles for plaunoi extract (Croton stellatopilosus Ohba) to treat dermatitis. Plaunotol, a constituent of plaunoi, has been shown to possess antimicrobial activity. In this work, 2 % w/w plaunoi-loaded formulations were prepared and investigated for their physical property (size and viscosity), efficacy and safety. The plaunoiloaded microemulsions (ME1-P (w/o), ME2-P (o/w)) and nanoemulsion (NE-P (o/w)) had different average sizes and apparent viscosities. Using modified Franz diffusion cell and a synthetic membrane, the release rate of plaunotol from NE-P was found to be the highest. With regard to the in vitro skin penetration, only o/w microemulsion (ME2-P) could deliver plaunotol through the newborn pig skin into the receptor fluid. Unlike ME1-P, the accumulation of plaunotol within the excised newborn pig skin was observed in ME2-P and NE-P. The antimicrobial property of the formulations was further investigated using a cylinder- plate method. Staphylococcus aureus, Staphylococcus epidermidis and Propionibacterium acnes were the tested gram microorganisms. It was found that the plaunoi-loaded formulations exhibited somewhat improved antibacterial activity for S. aureus and S. epidermidis when compared with the blank formulations. The skin irritation was not observed in all treated rabbits for the nanoemulsion NE-P. Both ME1-P and ME2-P showed slight erythema. These results suggest a potential use of nanoemulsions for topical delivery of plaunoi extract.