| Quercetin (3,3',4',5,7-pentahydroxyflavone) is a naturally occurring flavonoid found in all aerial plants. In recent years, it was found to posses a variety of biological activities, such as antitumor, antiviral, antioxidation, degrade blood pressure, anti-inflammatory, etc. Meanwhile, few side effects have been published. With poor solubility in water, quercetin can be absorbed little by the gastrointestinal tract, and its relative bioavailability is very low.We investigated the solubility of quercetin in various vehicles and the interaction between oils, surfactants, and cosurfactants.The basic components of the formulation were determined. Through drawing the pseudoternary phase diagram of microemulsion (ME) , the ME area had been found. Selecting the solubility of quercetin and average particle as the response variables to optimize the ME formulation, the final formulation (containing Tween-80 48%, PEG400 45%, ethyl oleate 7%) had been found.By comparing the solubility of quercetin ME and surfactants micelle solution, we validated that the ME could improve the solubility of the drug evidently. The ME could form oil-in-water ME when diluted with water. The ME presented as small spherical drops under electron microscopy, with the average diameter of 38.9 nm. Its basic character parameters such as refraction, electric conductivity, Zeta potential, viscosity were 1.3360±0.0003, 98.6±3.8μs·cm-1, -6.75±0.54 mV, 2.13±0.05mm2s·-1 respectively. The test of influencing factors and primary stability indicated that the quercetin ME could keep stable at room temperature and no-light conditions for 6 months.Because of the biotransformation of quercetin in its absorbing course, the drug concentration in plasma was very low. It was difficult to determine the absorption of quercetin by the drug concentration in blood because there were several kinds of transformed products in blood.After given to mouse, the drug both not absorbed in...
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