Update on Sirolimus Drug-Eluting Stents

Nicholas      Kipshidze; Martin   B.   Leon; Mykola      Tsapenko; Robert      Falotico; Gregory   A.   Kopia; Jeffrey      Moses

Abstract

Percutaneous transluminal coronary angioplasty (PTCA) has become the main method of coronary revascularization. However, despite technical advancement, restenosis with incidence rate of 30 to 50% remains a major limitation to the long-term success of PTCA. The introduction of stents has significantly improved capability of interventional cardiology in treatment and prevention of restenosis. Recent experimental studies in animals, clinical studies in humans and multi-center randomized clinical trials with Sirolimus-eluting stents, have demonstrated a significant reduction in vasculoproliferative response with no intimal tissue growth. Moreover, no significant adverse clinical events have been reported at long-term follow-up and first studies that explored the potential of this technology for the treatment of in-stent restenosis demonstrated safety and efficacy. Although the first clinical experiences with drug-eluting stents have produced stunning results, there are a number of theoretical limitations to these devices, including: 1) limitations of drug loading capacity and 2) ability to control drug elution that could result in unfavorable pharmacokinetics. There are also questions about the durability of the polymer coatings (deformation under mechanical stress, gaps between metal and arterial wall, etc). The thickness of some coatings makes them unsuitable for very small vessels. Finally most biodegradable coatings are prone to chronic inflammation. Since only a polymer-coated bare metal stent remains following the drugs release, the potential for long term polymer biocompatibility problems remains a concern. The potential for some drugs to produce radiation-like effects such as “black holes”, malapposed and naked struts and wall thinning are potentially the dark side of this technology and may contribute to late thrombosis, aneurysms or delayed restenosis. Long term clinical follow-up is necessary to assess the long term safety of this technology. There is a legitimate question as to whether drug-eluting stents will produce similar results across all patient subsets encountered in “real-life” interventional practice (e.g. long lesions, small diameter vessels, vein grafts, chronic total occlusions, bifurcated and ostial lesions). Cost-benefit issues also need to be addressed, especially because multivessel stenting and multistent usage is likely to increase.

Keywords: Sirolimus, pharmacokinetics, aneurysms, biocompatibility