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 The results may help doctors walk a tightrope in treating the
tremors and muscle rigidity of Parkinson's itself, where the
beneficial effects of levodopa wane over time, producing so-called
"off" times. Efforts to shorten the off times by increasing the
levodopa dose lead to the other unwanted movements, a condition
known as levodopa-induced dyskinesia (LID).
LID arises in more than half of Parkinson's patients who have taken
levodopa for four to six years and in more than 90 percent of
patients who have been on the drug for a decade. The disease itself
affects nearly a million people in the U.S., according to the
Parkinson's Disease Foundation.
In the new study, when 58 patients were given placebo for 12 weeks,
they improved by 8.0 points on a test designed to measure their
symptoms that has a maximum score of 104. But for the 63 people on
extended-release amantadine, the improvement was 15.9 points.
And when doctors looked at patients’ off times, they found
amantadine decreased the duration by about 34 minutes per day
compared to placebo recipients, who saw the duration of their
unwanted movements increase by about 18 minutes.
"This would be the first medicine, if approved, to take care of the
dyskinesia and the off times," lead author Dr. Rajesh Pahwa,
director of the Parkinson's Disease and Movement Disorder Center at
the University of Kansas Medical Center in Kansas City, told Reuters
Health.
The study, known as EASE LID, did not compare this formulation of
amantadine to other LID therapies, including immediate-release
amantadine, which has to be taken two or three times a day. The
manufacturer, California-based Adamas Pharmaceuticals, paid for the
test. The long-acting version used in the current study is also
known as ADS-5102.
"The results demonstrated that extended-release amantadine was well
tolerated, safe, and effective for the treatment of LID," Dr. Aparna
Wagle Shukla of the University of Florida, Gainesville writes in an
editorial in JAMA Neurology, where the study appears. "It remains to
be established whether the benefits of this new pill will justify
the cost."
But the drug has side effects, including insomnia, agitation,
constipation, dizziness and, most commonly, hallucinations, which
were experienced by nearly one out of four patients. Those unwanted
properties caused one in five patients to discontinue the drug, a
rate three times higher than seen with placebo.
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Immediate-release amantadine is not approved as a treatment for
dyskinesia, but some doctors prescribe it anyway despite limited
evidence, Pahwa said. Attempts to use nicotine, marijuana or the
antiepilepsy drug levetiracetam as therapies have shown even less
promise.
The experimental drug was given in the evening so blood levels would
peak around noon, when LID symptoms are most likely to appear. The
timing is also less likely to cause insomnia.
In addition to the hallucinations experienced by nearly a quarter of
the drug recipients, other prominent side effect included swelling,
dizziness, dry mouth, constipation and falls.
The researchers said the visual hallucinations were easily tolerated
and didn't affect a person's normal function. Only one of the drug
recipients reported a severe hallucination. Five of the 15 who
reported hallucinations discontinued treatment.
"All Parkinson's medicines in general can cause hallucinations,"
Pahwa noted. With the experimental drug, "some can have
hallucinations five minutes a day once a week. It's something
patients need to be aware of."
SOURCE: http://bit.ly/2sf4fgU JAMA Neurology online, June 12, 2017.
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