Drug therapy can vary following insertion of a stent

Q: I had angioplasty of two coronary arteries 18 months ago. I take aspirin and clopidogrel (Plavix) daily. Will I always need to take both drugs?

A: After a blocked heart artery is opened with a balloon, a wire mesh called a stent is left behind to keep the artery open. Standard therapy is aspirin and a second drug that also helps prevent blood clots. Clopidogrel is the one most commonly prescribed. How long a person should take both drugs remains an open question.

The first stents contained only bare metal. In some people, the bare metal triggers blood clot formation inside the stent. This is rare, but when it happens, it can cause a deadly heart attack.

After the stent is placed, the metal will get covered naturally by the same kind of cells that line normal blood vessels. They are called endothelial cells. This process takes three to four months.

In the meantime, people take aspirin and a second anti-platelet drug for three to six months to prevent clots. This is known as dual anti-platelet therapy. Anti-platelet drugs help prevent platelets in blood from clumping together to form clots. After dual therapy, the patient takes aspirin alone, with no fixed end point.

But there's another problem with bare metal stents. About 10 percent of patients receiving a bare metal stent have too much growth of endothelial cells into the stent. This can continue for one to two years, or even longer. The excess growth can cause another blockage inside the bare metal stent.

Because of this problem, a new type of stent was developed. These stents are coated with a drug that helps prevent endothelial cells from forming over the metal. They are called drug-eluting stents.

With the newer stents, there's much less chance of extra buildup of the endothelial cells. But this also means that the metal does not get completely covered in new cells. So the risk of a sudden blood clot lasts longer. And this requires longer dual anti-platelet therapy.

Experts recommend dual therapy for a least one year. But even after a year, stopping the second drug increases the risk of a sudden clot in the stent. Stopping also increases the risk of a heart attack and stroke, unrelated to the site of the original angioplasty.

Talk with your doctor about your bleeding risk. That will be the major factor in determining aspirin only or dual anti-platelet therapy.

(Howard LeWine, M.D., is a practicing internist at Brigham and Women's Hospital in Boston and Chief Medical Editor of Internet Publishing at Harvard Health Publications, Harvard Medical School.)

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