Biodegradable Stent Successful in Human Trial

By Ed Edelson
HealthDay Reporter

THURSDAY, May 31 (HealthDay News) -- A stent that biodegrades and vanishes from an artery in a matter of months has successfully passed a major test in humans, German researchers report.

The device, made of magnesium, is one of many different biodegradable stents that together represent the future of these artery-opening devices, said Dr. Raimund Erbel, professor of medicine at the West German Heart Center in Essen, and lead author of a report on the trial in the June 2 issue of The Lancet.

Stents are tiny, implanted mesh tubes that prop open failing arteries.

"In the long run, a biodegradable stent is best for those who need a coronary stent," Erbel said. "When such a stent has done its job, you don't need it any more. In the long run, its presence can cause problems."

A number of cardiologists and companies in countries across the world are working to develop stents that are broken down by the body once they have succeeded in keeping blood flowing through an artery. Most of this work is going on outside the United States, with reports on early trials coming from China, Japan, Finland, Germany, and elsewhere.

For example, at a heart meeting earlier this year, a group at Erasmus University in Amsterdam reported on a biodegradable stent they placed in 30 cardiac patients. The devices behaved very much like standard metal stents over the relatively brief period of a month, the researchers reported. The patients are still being followed to determine exactly when and how the stents disappear.

In this new trial, Erbel and his colleagues implanted 71 magnesium stents in 63 patients.

They reported that the safety record of the devices remained good after 12 months, with not a single case of clotting noted within the stent and no incidents of heart attack or death among patients. The diameter of the treated arteries increased slightly as the magnesium was absorbed by the body, being replaced by natural calcium and phosphorus.

As a bonus, the patients did not require treatment with clot-dissolving drugs such as Plavix and aspirin -- medicines that are typically needed with today's permanent metal stents.

The magnesium devices were far from perfect, however. Re-blockage of an artery occurred in 47.5 percent of patients, with 27 percent of them requiring artery-opening procedures.

One unexpected benefit of the magnesium stents was that it allowed the cardiologists to see what was happening inside the devices by using either MRI or CT scans. "Such views are hard to get with current devices, but we could get a wonderful visualization of an artery," Erbel said.

He views magnesium as a natural material for a degradable stent, because it is easily handled by the body. "After four months, everything is gone," Erbel said. "In fact, the degradation process was, in our opinion, too rapid, something we are researching," he said.

Joachim Kohn, director of the New Jersey Center for Biomaterials at Rutgers University, disagreed that biodegradable magnesium stents are the wave of the future.

"I'm familiar with this and don't think it will work very well, in spite of the early positive results," Kohn said. "We are going to see a number of complications in the end stages of the degradation of magnesium. It is a revolutionary and very innovative idea, but, in the end, we are better off with a body-like material than with a metal."

Kohn has developed a stent that uses just such a synthetic "biomaterial." It has been licensed to a small company, REVA Medical, with first human tests scheduled to begin this month.

Almost all the degradable stents now under development use such synthetic materials, which helps explain why so little is being done in the United States, Kohn said.

"Biomaterials were hot in the 1990s," he said. "Everyone in the United States was interested in biomaterials. But a field has to be matured, and before that happened, we moved on to other things, such as nanomaterials."

Wherever the work is done, "there is no question that we will want a biodegradable stent eventually," Kohn said. "There are persistent issues with permanent stents." It will take years to get such stents into routine medical use, he said, because careful human testing will be required.

SOURCES: Raimund Erbel, M.D., professor, medicine, West German Heart Center, Essen; Joachim Kohn, Ph.D., director, New Jersey Center for Biomaterials, Piscataway; June 2, 2007, The Lancet

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