People taking two drugs to treat symptoms of Parkinson's disease may be at risk of heart valve damage, a potentially life-threatening side-effect, two studies on European patients suggest.
The drugs are pergolide, sold as Permax, and cabergoline, sold as Dostinex. The medications are not the main treatment for the disease, which affects about six million people worldwide.
In Thursday's New England Journal of Medicine, Italian researchers said about one-quarter of 155 patients taking pergolide or cabergoline had moderate to severe heart valve problems compared with a control group.
A second study of records from 11,400 Parkinson's patients in the United Kingdom that appears in the same issue found those taking either drug were five to seven more likely to have leaky heart valves compared to those taking other therapies.
"This is an extraordinarily high risk," said Dr. Bryan Roth, a pharmacology professor at the University of North Carolina at Chapel Hill.
"It's a bad side-effect. As far as I know, there are no medications that can reverse it" and valve replacement surgery is the only solution, he said.
Roth wrote commentary on the research in the journal, saying he suspected that the drugs stimulate a receptor in the heart that is related to valve disease. Roth urged companies developing new drugs to screen them against the heart receptor during safety testing.
Leaky heart valves
The heart valve problem led U.S. regulators to pull the diet drug fen-phen from the market in 1997.
Eli Lilly and Co., makers of Permax, had estimated the risk of valve damage from the drug was five in 100,000 users. Drug labels do not indicate an increased risk for valve disease.
Symptoms of valve disease include extreme weakness, shortness of breath, pain in the chest and difficulty with exertion. Patients should talk to their doctor about the increased risk before making any treatment decisions.
Pergolide is also used to treat restless leg syndrome, a condition in which patients feel a crawling sensation in their legs and an urge to move them.
The drug is approved for use in Canada as a treatment for Parkinson's.
Cabergoline is approved in the U.S. for treating excessive levels of the hormone prolactin in the blood, but not for Parkinson's. It is not listed in Health Canada's database of approved drugs and is not available for sale in the country.
Parkinson's disease can lead to tremors and loss of muscle control.
The disease is caused by a lack of dopamine in the brain. The drug levodopa, which leads the body to make more dopamine, is the main treatment.
The Italian study was paid for by the Milan clinic and two Parkinson's foundations, while the Canadian government and a drug company provided partial support for the other study.
Many authors of both studies have consulted for makers of Parkinson's drugs.