New Type of Parkinson's Disease Drug
Potential New Parkinson's Disease Treatment Shows Promise
Aug. 21, 2003 -- For decades, dopamine-replacement drugs have reigned as the best defense against Parkinson's disease. But new research shows that a drug that doesn't affect dopamine may improve symptoms without causing some of the troubling side effects of current drugs.
Researchers say dopamine replacement drugs are an effective Parkinson's disease treatment in the short term but eventually lose their punch over time. After several years, the drugs work for shorter lengths of time and Parkinson's disease symptoms -- such as involuntary twisting and turning (dyskinesias) -- return.
When this happens, increasing dopamine drugs worsens dyskinesias, and reducing dopamine drugs worsens the slowness, stiffness, and tremors also seen in Parkinson's disease patients.
Silver Lining for Parkinson's Disease Treatment
But researchers say they have discovered a drug, called istradefylline, that may offer new hope.
Once patients with Parkinson's disease develop problems with both muscle coordination and dyskinesias, it is very difficult to provide further benefit with dopamine medications, says researcher Robert Hauser, MD, director of the Parkinson's Disease and Movement Disorders Center at the University of South Florida, in a news release.
This study opens the door to the possibility of providing additional benefit for advanced Parkinson's disease patients and confirms the idea that medications that affect brain chemicals other than dopamine can provide benefit in Parkinson's disease, he says.
During a four-month study sponsored by Kyowa Pharmaceuticals, researchers evaluated 80 patients with advanced Parkinson's disease who had been taking the dopamine drug levodopa for at least a year and were showing signs that the effects of the medication were wearing off. However, changes in current Parkinson's disease treatment were not permitted.
Researchers separated the patients into three groups:
Group one took levodopa and a placebo.
Group two took up to 20 mg per day of istradefylline.
Group three took up to 40 mg per day of istradefylline.
Volunteers noted how well their medication was controlling their symptoms -- tremors, slowness, and stiffness -- and whether they were experiencing any dyskinesias.
Istradefylline reduced Parkinson's disease symptoms by 1.7 hours per day. Overall, researchers found that istradefylline didn't worsen severity of dyskinesia and was generally well tolerated by the volunteers.
How the New Drug Works
Rather than affecting dopamine in the brain, istradefylline stimulates a brain receptor called adenosine A2A. Earlier studies show that in animal studies of Parkinson's disease treatment, istradefylline changes the firing of nerve cells in a way that improves nerve and muscle function in people with the Parkinson's disease. But researchers say more work is needed before the drug can be made available for use.
"We may be able to reduce the time patients are 'off' (medication benefit having worn off) with slowness, stiffness, and tremors without worsening the severity of dyskinesia. With dopamine medications alone, this is difficult to do," says Hauser.
SOURCES: Neurology, Aug. 12, 2003. News release, University of South Florida.