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Clinical alert issued for drug-eluting stents and late thrombosis

The US-based Society for Cardiovascular Angiography and Interventions (SCAI) has released a clinical alert advising physicians to manage the risk of a rare but serious complication associated with the use of drug-eluting stents

The US-based Society for Cardiovascular Angiography and Interventions (SCAI) has released a clinical alert advising physicians to manage the risk of a rare but serious complication associated with the use of drug-eluting stents.

The document was released after hearings held by the FDA's Circulatory Systems Device Panel regarding the use of these devices. The panel supported the continued use of these devices, but suggested that more research was needed to determine whether the devices contribute to an increased risk of myocardial infarction and death in complex heart disease patients who are fitted with such stents.

Drug-eluting stents are mesh tubes that prop open narrowed arteries in the heart while slowly releasing a medication that prevents the build-up of scar tissue inside the stent. These tiny devices have been very successful in preventing renarrowing, or restenosis, of the coronary arteries, reducing the rate of this complication by 40ñ60 per cent, compared with their bare metal counterparts.

Several recent analyses that tracked patient outcomes for four to five years after stent placement showed that blood clots were slightly more likely to form inside a drug-eluting stent than inside a bare metal stent. It remains unclear, however, how large the difference in risk is. Data suggest, however, that in the types of lesions treated in the original controlled trials clotting was about 0.2% in excess (compared with bare metal stents) per year after year one. When this occurs, the patient may suffer myocardial infarction or death.

Published in SCAI's official journal, the paper, entitled Catheterisation and Cardiovascular Interventions, focuses on the importance of careful patient selection, stent implantation and consistent use of medications to prevent the delayed formation of blood clots blocking blood supply to the heart, a condition known as late stent thrombosis. Several large multicentre trials are underway to better define the risk of late stent thrombosis and assess strategies to prevent such complications.

The only two drug-eluting stents available on the US and EU market are Cordis' CYPHER sirolimus-eluting stent and Boston Scientific's TAXUS paclitaxel-eluting stent system. A number of new second and third generation stent technologies are in research, clinical trial phases, or have achieved marketing approval outside the US.

US-based drug delivery firm Conor MedSystems' new stent design was approved in Europe in February 2006. The CoStar stent uses a bioresorbable polymer to deliver the anti-restenosis drug, so that after a few months of drug elution, it becomes a bare metal stent, which may eliminate the risk of late stent thrombosis present in permanent polymer stents.

Elsewhere, US pharmaceutical company, Abbott, and Germany-based Biotronik are testing a completely bioabsorable stent which disappears after the drug has been eluted. Hong-Kong-based OrbusNeich received CE mark approval in 2005 for its Genous stent, which, rather than using drugs to suppress excess tissue growth, employs a bio-engineered coating to attract a thin endothelial layer within hours. A number of other companies, such as Biosensors and Xtent, are working on other drug/ polymer/ stent combinations.

In its most recent quarterly filing, Boston Scientific, estimated that the coronary stent market for 2006 was roughly USD 6 billion worldwide, with 90 per cent of revenues generated from drug-eluting stents.

24th January 2007

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