No Advantage with Biodegradable-Polymer Stents: Meta-Analysis

November 08, 2013

NEW YORK, NY – New stents with a biodegradable polymer are superior to first-generation drug-eluting stents (DES) when it comes to reducing target vessel revascularization (TVR) but are not better than newer-generation stents with a durable polymer, according to the results of a new meta-analysis [1].

In fact, among the stents compared, newer-generation stents with durable polymer, such as the zotarolimus-eluting stent (Resolute, Medtronic), cobalt-chromium everolimus-eluting stent (Xience, Abbott Vascular), and platinum-chromium everolimus-eluting stent (Promus, Boston Scientific), had the lowest rates of TVR, whereas the cobalt-chromium everolimus-eluting stent was shown to be the safest.

"I would say that not all polymers are the same," Dr Sripal Bangalore (New York University School of Medicine) told heartwire . "We previously believed the polymers were bad, but it's not true. There are data—plenty of ex vivo and animal model data—suggesting that the fluoropolymer, which is actually seen on the cobalt-chromium everolimus-eluting stent, is less thrombogenic and inflammatory, even when compared with a bare-metal stent."

The net result is that the new-generation durable-polymer stents, particularly the cobalt-chromium everolimus-eluting stent, have a significant advantage over biodegradable-polymer drug-eluting stents and provide a superior combination of efficacy and safety, report the investigators.

The results were published online November 8, 2013 in BMJ.

Conversion to a Bare-Metal Stent

At present, several companies make stents with a biodegradable polymer, and some are available in Europe, where they have CE Mark approval, but they are not yet available in the US.

To heartwire, Bangalore said the reason that the biodegradable stents were developed in the first place was to exploit the safety of a bare-metal stent and efficacy of a durable-polymer DES. First-generation DES were associated with very late stent thrombosis and the late catch-up phenomenon—an increase in restenosis rates with the Cypher (Cordis/Johnson & Johnson) and Taxus (Boston Scientific) stents after one year. The risk of stent thrombosis and restenosis were attributed to some of the characteristics of the polymer that led to inflammation and malapposition.

"Biodegradable polymers were developed to have the early efficacy of the DES," said Bangalore, "and then the polymer is absorbed and converts the stent into a bare-metal stent, so that you have the late safety associated with a bare-metal stent."

Although the bioabsorbable polymer-based stent was developed because it was considered superior to a bare-metal stent, Bangalore said that they have published data in the past 18 months showing the that cobalt-chromium everolimus-eluting stent is actually safer than traditional bare-metal stents. "If that is true, then the whole hypothesis behind the bioabsorbable polymer is questionable," he told heartwire .

The meta-analysis included 126 randomized trials and 258 544 patient–years of follow-up. Regarding efficacy, biodegradable-polymer DES were superior to first-generation paclitaxel- and zotarolimus-eluting stents in the reduction of TVR. However, there was no difference in the rate of TVR between biodegradable-polymer DES and newer-generation DES with durable polymers.

Regarding the long-term safety, the biodegradable-polymer DES reduced the rate of stent thrombosis compared with paclitaxel- and sirolimus-eluting stents but were inferior to the cobalt-chromium everolimus-eluting stent. Compared with the cobalt-chromium everolimus-eluting stent, however, the biodegradable-polymer DES were associated with a 48% increased risk of death, according to a one-year landmark analysis.

In addition, the meta-analysis showed the cobalt-chromium stent to be the safest, with a 65% reduction in definite stent thrombosis, a 35% reduction in MI risk, and a 38% reduction in risk of death compared with bare-metal stents.

Need to Show Some Advantage

The new results, said Bangalore, confirm two things. One, the bioabsorbable-polymer stent hypothesis is true, but only when compared with bare-metal stents and first-generation DES. "When [bioabsorbable-polymer stents] are compared with newer-generation drug-eluting stents, there was actually low superiority in the outcomes we examined."

The present trials of stents with bioabsorbable polymers are noninferiority studies, noted Bangalore, and have not shown superiority over the new-generation durable-polymer DES, even with regard to use of dual antiplatelet therapy. At present, there does not appear to be any advantage to the bioabsorbable-polymer stents with regard to safety or efficacy, he added.

"We need more data to show that biodegradable polymer stents offer some advantage," said Bangalore. "Most of the benefit has been assumed to be late, when the stent converts to a bare-metal stent. We need trials that are powered to show superiority of these [biodegradable polymer stents] over new-generation drug-eluting stents [with a durable polymer], especially the cobalt-chromium everolimus stent. At the very least, we need trials showing that there are other advantages, such as reduced dual antiplatelet therapy requirements."

Bangalore reports participating on advisory boards and/or consulting for Boehringer Ingelheim, Daiichi Sankyo, Pfizer, Gilead, Abbott, and Abbott Vascular. The present analysis was not funded by any specific grants from the public, commercial, or not-for-profit sectors.

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