Effects of Aqueous Medium, Tween-20 and Flow on the Stability of Sirolimus

Abstract

Sirolimus-eluting stents have been widely used in the treatment of coronary artery disease. Prior to the clinical application, the in vitro drug release test is a mandatory requirement for the quality control of sirolimus-eluting stents. How to maintain the stability of sirolimus in the release medium is an important issue throughout the drug release research. In this study, the stability tests of sirolimus in three aqueous media (ultrapure water (UPW), normal saline (NS) and phosphate-buffered saline (PBS, pH 7.4)) were carried out. It was found that the half-lives of sirolimus in UPW, NS and PBS (pH 7.4) were, respectively, 111.8, 43.6 and 11.5[Formula: see text]h. Tween-20 was then added to the above-mentioned three aqueous media and was shown to improve the solubility and stability of sirolimus in aqueous solutions. Under static conditions, the half-life value for sirolimus was significantly increased in the presence of Tween-20 (UPW, 3.5-fold; NS, 2.0-fold; PBS (pH 7.4), 2.7-fold). The effect of solution flow on the stability of sirolimus was also investigated in a flow loop apparatus to mimic vessel-like flow conditions. There was a significant decrease in the stability of sirolimus in aqueous media with the increase of flow rate. The results suggest that aqueous solution supplemented with Tween-20 could be used as the release medium for sirolimus-eluting stents, and that the circulation of the release medium should be controlled at low flow rate.

The Effect of Fluid Shear Stress on the In Vitro Release Kinetics of Sirolimus from PLGA Films

“…Sirolimus is very unstable in various aqueous solutions and has poor water solubility [ 58 , 59 , 60 , 61 ]. According to our previous work, the aqueous solution was supplemented by Tween-20 (4 g/L) to increase the stability and solubility of sirolimus, thereby attaining a favorable sink condition for the sirolimus release experiments [ 62 ]. However, the Tween-20 aqueous solution in this research could not really simulate the blood components.…”