The drug-eluting stent (DES) is no stranger in med-tech headlines. The popular, yet frequently-debated technology has dominated industry news for the past year or more.

Now there's a new type of DES being investigated – this one designed to prevent blockages in arteries outside the heart.

The first U.S. patients in the pivotal Phase II trial of the Zilver PTX stent, made by Cook Medical (Bloomington, Indiana), were treated at Tri-City Medical Center (Oceanside, California), the company reported Monday. The patients were treated by principal investigator Richard Saxon, MD, assistant clinical professor of radiology at the University of California, San Diego , as part of the international Zilver PTX Stent Trial.

"Drug-eluting stents that combine a metal scaffold with a drug were first applied in the heart, and the results have been very good," Saxon said. "And it is hoped similar technology, used in the legs, will help those who suffer from peripheral arterial disease [PAD]."

The trial is intended to evaluate the stent, eluting the drug paclitaxel, in treating PAD, a condition that affects more than 10 million Americans each year, Cook said. The study aims to determine if the same type of DES technology found in DES devices used to open blockages in the coronary arteries can be used to treat blockages in arteries outside the heart.

Following successful safety testing during the trial's Phase I enrollment, Cook said it will enroll more than 700 patients in the Phase II trial that will be used to support submission to the FDA for marketing approval.

In February Cook reported that the Zilver PTX Phase I trial results demonstrated no stent fractures (Medical Device Daily, Feb. 1, 2007). Cook said that the major adverse event rate was equivalent to conventional balloon angioplasty treatment at the six-month follow-up point.

Rob Lyles, VP and global leader of Cook's peripheral intervention division, told Medical Device Daily that the Zilver PTX trial is the only ongoing trial for PAD with a stent/drug combination. There were some earlier trials in this area initiated by some competing companies, he said, but so far there are no FDA approved DES devices on the market for the PAD application.

"That's what's novel about this and that's what's exciting for us," Lyles said.

One thing that makes the Zilver PTX stent unique, Lyles said, is that it is a self-expanding stent as opposed to a balloon-expanding stent. The difference, he said is the self-expanding stent's ability to flex and move, and then bounce back to the shape it is supposed to be in.

This is particularly important, he noted, when dealing with arteries in the legs, which bend frequently. If a person took a hard blow to the thigh, for example, and had a balloon-expandable stent, the blow could potentially crush the stent. But the self-expanding stent, he said, would simply spring back into place.

Parallel to the use of a coronary DES, the Zilver is intended to prevent restenosis.

But Lyles told MDD that the Zilver PTX is unique because, unlike coronary DES, a polymer-free technology is used to coat the device with paclitaxel. Coronary stents, he said, use polymer, an added substance to hold the drug on the stent, and he referred to the debate suggesting that the polymer may be the cause of thrombosis or other adverse events in DES use.

In many cases, according to Cook, PAD patients who have been treated with balloon angioplasty/stenting experience restenosis over time and must undergo more invasive treatment such as bypass surgery to reopen the arteries. The Zilver PTX trial will determine whether the stent/paclitaxel combination will keep arteries open over time as has been shown with coronary DES technology, the company said.

The trial is being conducted at 28 U.S. locations and is the first device trial ever conducted simultaneously in the U.S. and Japan, Lyles said. Clinical data collected on Japanese and U.S. patients will be combined for the final evaluation of the device and used for regulatory submissions in both markets for approval. The trial will enroll patients who will be randomized to receive either the Zilver PTX stent or balloon angioplasty.

This is particularly exciting news for Japan, Lyles said, because their rigorous regulatory process tends to keep Japan seven to 10 years behind the U.S. in terms of the technology available there. Lyles said it has become a public policy issue for Japan and that the Japanese regulatory agency has worked closely with the FDA to close the technological gap between the two countries.

So for a device trial to enroll patients at the same time and be happening simultaneously in the U.S. and Japan will give Japanese patients faster access to the technology, he said.

PAD affects blood vessels that lead from the heart to other areas of the body, such as the legs, feet and kidneys. When the blood vessels become blocked due to the build-up of fatty deposits, blood circulation is restricted. Untreated, PAD results in pain when walking and can lead to gangrene and amputation.

"About 300,000 patients in the U.S. right now every year receive some type of amputation," Kian Olsen, product manager of the Zilver PTX, told MDD. "This is the first step in treatment of this lower-limb disease. Peripheral artery disease … is not a life-threatening disease. It is a lifestyle-threatening disease though."

In the end, Olsen said, Cook's goal is to "reduce amputation rates by trying to improve wound healing and better circulation."

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