Keywords: 
• total flavonoids from Oxytropis falcata Bunge /
• physicochemical properties /
• solubility /
• the apparent oil-water partition coefficient /
• percutaneous permeability

Abstract: Objective To investigate the physicochemical constants such as the solubility and the apparent oil-water partition coefficient of total flavonoids from Oxytropis falcata Bunge and study the in vitro percutaneous permeability for providing the reference for the design and preparation of transdermal drug formulations. Methods The solubility of total flavonoids from Oxytropis falcata Bunge in water and different solvents were determined by ultraviolet spectrophotometry. The apparent oil-water partition coefficient of n-octanol/water buffer solution was also determined. Percutaneous penetration of total flavonoids from Oxytropis falcata Bunge was investigated by a double-chamber osmotic diffusion device with rat isolated skin as a model. Results The total flavonoids from Oxytropis falcata Bunge had good solubility in methanol, ethanol and phosphate buffer at pH 5.0-7.4. The apparent oil-water partition coefficient(P) of total flavonoids from Oxytropis falcata Bunge had a certain relationship with the pH of the solution. At 2.5-7.4, the lgP value of total flavonoids decreased with increasing pH value and the lgP value is between 0.38 and 1.34. The cumulative amount of drug in 24 hours is 155.44 μg/cm² and the time lag was (11.52±0.95) h. Conclusion The total flavonoids from Oxytropis falcata Bunge had poor water solubility, but were more soluble in ethanol, methanol and phosphate buffer at pH 5.0-7.4. The skin permeability was not high, and the cumulative transmittances was low with a time lag. The above characteristics should be considered comprehensively in the design of transdermal drug dosage forms.