Abstract: 【Objective】 This experiment was to develop a composite nanoemulsion of Eucalyptus oil and peppermint oil to lay a foundation for clinical application.【Method】 The nanoemulsion was prepared by phase transition method.The formulation and process were optimized by single factor test and pseudo-ternary phase diagram method.The type was determined by staining method.The morphology and particle size distribution were determined by transmission electron microscopy and particle size analyzer.The content of the main components was determined by high performance liquid chromatography.Stability test was carried out under different temperature and humidity conditions.In vitro antibacterial test was carried out by double dilution method and micro chessboard dilution method.【Result】 The optimal formula of nanoemulsion was:Polyoxyethylene castor oil EL 28.54%,1,2-propylene glycol 9.51%,Eucalyptus oil and peppermint oil mixed solution with 1,8-cineole and menthol in a ratio of 10∶1 9.51%,and distilled water 52.43%.The prepared nanoemulsion was oil-in-water type with dilution stability.The morphology was uniformly distributed spherical,with Zeta potential of －3.16 mV,average particle size of 14.6 nm,and polydispersity index (PDI) of 0.211.The content of Eucalyptus oil and peppermint oil in the composite nanoemulsion were 55.98 and 5.61 mg/mL，respectively.In the accelerated test,the solution remained clear and transparent,and the contents of 1,8-cineole and menthol changed to 53.85 and 5.32 mg/mL,respectively.In the long-term test,the solution was stable,and the contents of 1,8-cineole and menthol changed to 53.50 and 5.33 mg/mL,respectively,and the changes of solution content were in accordance with the requirements.In vitro antibacterial tests showed that,for Salmonella,the MIC and MBC values of the composite nanoemulsions were 1/2 and 1/4 of those of the Eucalyptus oil nanoemulsions and 1/32 of those of the peppermint oil nanoemulsions,respectively.For Escherichia coli,the MIC and MBC values of the composite nanoemulsions were 1/4 and 1/2 of those of the Eucalyptus oil nanoemulsions and 1/128 and 1/32 of those of the peppermint oil nanoemulsions,respectively.For Staphylococcus aureus,the MIC and MBC values were 1/2 and 1/8 of those of Eucalyptus oil nanoemulsion and 1/32 of those of peppermint oil nanoemulsion,respectively.Therefore,the composite nanoemulsion had good antibacterial properties,and the combination of the two drugs showed an additive effect on Salmonella and Escherichia coli,and a synergistic effect on Staphylococcus aureus,without antagonistic effect.【Conclusion】 The composite nanoemulsion preparation was prepared by phase transition method and pseudo-ternary phase diagram method.The process was simple,met the quality requirements of nanoemulsion,and provided ideas and methods for the preparation of aqueous solvents for poorly soluble drugs.

Key words: Eucalyptus oil; peppermint oil; composite preparations; nanoemulsion; antibacterial activity