In vitro study of release mechanisms of paclitaxel and rapamycin from drug-incorporated biodegradable stent matrices.

We have studied the in vitro release kinetics of two important antirestenosis drugs from biodegradable stent matrices. A helical stent incorporating drugs was exposed to buffer, and both degradation-controlled and diffusion-controlled drug releases were observed. New methods for in vitro drug release for both paclitaxel and rapamycin have been developed. The release profile shows a slow diffusion-controlled phase, followed by a more rapid degradation-controlled region. In the early part of the drug release, no burst effect is observed for either drug. This might be significant for paclitaxel administration, where cardiotoxicity has been sometimes of concern. By suitable polymer/drug formulations, it is possible to develop controlled release stent matrices that can exhibit a variety of release profiles. These release profiles may have relevance to antirestenotic effects and to local or systemic toxic effects.