A study on distribution and stability of drugs at the interface of a scutellarin-loaded emulsion

This work mainly studies the interfacial behaviors of scutellarin on a newly developed emulsion and establishes a three-phase distribution model. The results showed that the concentration of scutellarin could decrease the interfacial tension and the gel-liquid crystal phase transition temperature of phospholipids. By observing the micromorphology of the emulsion, it is inferred that the drug exists on the emulsion interface. The distribution of drugs in three phases at different pH was calculated. The results showed that when pH was in the range of 3.0-8.0, the content of scutellarin in the oil phase was less than 0.25%; when pH < 7.4, more than 88% of the drugs were on the interface; when pH > 7.4, the drugs were mainly distributed in the aqueous phase. Therefore, the behavior of emulsions (pH 6.0) in vitro and in vivo is mainly composed of the behavior of drugs on the interface. The study above can explain some properties of the emulsions after loading scutellarin. Including the decrease of particle size and stability constant Ke, the increase of zeta potential, and the decreased chemical stability after the pH value went higher.