Determination of entrapment efficiency and drug phase distribution of submicron emulsions loaded silybin.

This paper compared the performance of ultrafiltration (UF), ultracentrifugation (UC) and microdialysis (MD) for determining the entrapment efficiency (EE) of submicron emulsions (SE) loaded with a model drug, silybin (SB). Also, a novel way was created to evaluate the drug phase distribution of SE. The EE of SEI, SEII and SEIII with a range of particle sizes (109.8, 171.7 and 213.2 nm) and the drug phase distribution of SEII and SEIII were separately determined by the three methods. The EEs of SEI were 99.8%, 91.1%, 84.4% determined by MD, UF, UC, respectively, and the EEs of SEII and SEIII were 99.5%, 86.4%, 72.1% and 99.4%, 84.3%, 66.3%, separately. The accuracy of MD to determine EE of SE is much less than that of UF. Although UC is the fastest and most simple to use, its results are the least reliable. The sequence of the amount of drug in SE is as follows: O/W interface, aqueous phase and oil phase. Over 80% of SB was in the O/W interface of SEII and SEIII individually. The method created is reliable for quantifying the phase distribution of drug in submicron emulsions.