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This is ALL THINGS CONSIDERED, from NPR News, I'm Michele Norris.

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Researchers are warning patients with Parkinson 's disease that two drugs widely used to treat the disorder can damage heart valves. That can result in heart failure and even death. Some patients require surgery to replace leaky valves.

And as NPR's Richard Knox reports, the concern may extend beyond Parkinson's patients.

RICHARD KNOX: The drugs are pergolide and cabergoline. They are derived from a fungus called ergot. In addition to Parkinson's these drugs are used to treat restless legs syndrome and to help nursing mothers stop lactating.

One of the new studies involves more than 11,000 Parkinson's patients in the United Kingdom. Those taking either one of the ergot drugs were up to seven times more likely to have seriously leaky heart valves.

But the study from Italy was the real eye opener the researchers did echocardiograms on 155 patients taking drugs for Parkinson's. The substantial fraction of those on either on pergolide or cabergoline had damaged heart valves.

Dr. ANGELO ANTANENE (Parkinson's Expert): The risk is so high that about one third of people taking these drugs might develop heart valve disease.

KNOX: That's Dr. Angelo Antanene Parkinson's expert in Milan. He and his colleagues were startled by their studies outcome.

Dr. ANTANENE: It was much higher than I expected, because people didn't complain to0 much about this.

KNOX: Leaky heart valves can cause shortness of breathe and fatigue. But Parkinson's disease also causes fatigue. In Parkinson's the brain doesn't make enough of a chemical called dopamine needed for muscle movement.

Dr. ANTANENE: We probably attributed this - the fatigue, these patients were experiencing to the Parkinson disease rather than to the heart disease. And probably that's why we underestimated the problem.

KNOX: Parkinson's drugs aren't the first to cause this kind of heart damage. That's why the diet drug Phen-Fen was pulled from the market eight years ago.

One of the drugs in that combination activates a receptor on the surface of heart valves. The Parkinson's drugs do the same thing. Dr. Brian Roth(ph) of the University of North Carolina says when that receptor is activated heart valve cells grow too much.

Dr. BRIAN ROTH (University of North Carolina): The geometry of the heart valve has to be maintained very precisely. Even a small amount of overgrowth of the valve can cause the heart valve to become leaky and then you have problems.

KNOX: Roth helped unravel the Phen-Fen effect, his group has found that other drugs cause overgrowth of heart valves. One is a migraine drug called dihydroergotomine another is the recreational drug ecstasy.

Roth's group recently examined all over medications approved for sale in this country, and found some other problems.

Dr. ROTH: We haven't published that data yet, so I can't really say much about it. Other to say that there are probably a handful of other medications out there that may have this potential side effect.

KNOX: In that handful are there some that are widely used?

Dr. ROTH: I probably shouldn't say anything about this until the paper is published - but yes some are widely used.

KNOX: Experts say the new Parkinson's reports confirm smaller studies. Dr. Michael Oaken is Medical Director of the National Parkinson Foundation.

Dr. MICHAEL OAKEN (National Parkinson Foundation): We've seen these reports popping up and there has been sort of an alarm bell that has gone off within the field.

KNOX: It's especially striking because the ergot drugs have been used for decades in millions of patients. And the new studies in the New England Journal of Medicine come at a time when doctors have been using more of these times of drugs called dopamine agonist.

They cause the body to make more dopamine, they are used especially in younger Parkinson's patients, to avoid some of the problems with L-dopa, a mainstay drug for the disorder.

Oaken urges people who have taken pergolide or cabergoline to see their doctors for a heart checkup. Those on the drugs should consider switching to a different medication not derived from ergot.

Dr. OAKEN: Most of the time with these drugs the damage has been done. But the damage is also ongoing, and so if you don't get people off the drug, then they can continue to worsen.

KNOX: There is no evidence that patients taking non-ergot drugs prescribed for Parkinson's or Restless Leg Syndrome are at risk of serious heart valve damage. But the Italian researcher saw some minor valve abnormalities with them too. So they are also urging these patients to get their valves checked.

Richard Knox, NPR News.

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