THE main drug used to treat Parkinson鈥檚 disease may be about to take a back
seat, following this week鈥檚 announcement of successful trials of an alternative
drug that produces milder side effects.
Parkinson鈥檚 is caused by the death of cells that produce the chemical
dopamine, which transmits neural signals in the brain. As the disease
progresses, patients鈥� movement becomes impaired and they experience tremors,
muscle rigidity and general sluggishness.
For more than a decade, the main weapon against the disease has been L-dopa,
which the brain converts into dopamine. But L-dopa isn鈥檛 perfect. After years of
taking the drug, many people find that each dose provides shorter and shorter
periods of relief. L-dopa can also cause dyskinesia鈥攕udden, powerful
jerking movements of the limbs, head and neck.
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Surgery can help to fight these side effects, says Carl Clarke, a neurologist
at the University of Birmingham. 鈥淏ut the best thing to do is avoid them in the
first place.鈥� So Clarke has for the past five years been working with colleagues
from elsewhere in Europe, Israel and Canada to run a trial comparing 89
Parkinson鈥檚 patients taking L-dopa with 179 receiving ropinirole, manufactured
by SmithKline Beecham under the name ReQuip. Once patients receiving ropinirole
reached a designated maximum dose, their therapy was supplemented with
L-dopa.
At the International Congress on Parkinson鈥檚 Disease in Vancouver this week,
Clarke and his colleagues announced that ropinirole quelled symptoms just as
well as L-dopa alone, and produced fewer adverse reactions. 鈥淭his will cause a
fundamental shift in the way doctors treat this disease,鈥� predicts Clarke.
Nearly 46 per cent of the L-dopa patients in the trial experienced
dyskinesia, compared with only 20 per cent in the ropinirole group. The results
were even more dramatic among the one-third of ropinirole patients who didn鈥檛
require L-dopa supplements: only 5 per cent of them experienced dyskinesia.
Ropinirole is a newer member of an established class of drugs called dopamine
agonists, which mimic the action of dopamine on the brain. But medicines of this
kind have until now had problems of their own, such as causing severe nausea,
and so have been used mostly as supplements or short-term substitutes for
L-dopa.
Abraham Lieberman, national medical director of the National Parkinson
Foundation in Miami, agrees that the results with ropinirole shatter existing
dogma. 鈥淏efore this study, no one thought you could treat for five years with an
agonist,鈥� he says.
But Lieberman suspects that L-dopa will remain an important drug. Not only
did two-thirds of the ropinirole group in the new trial require it as a
supplementary therapy, he says, but some Parkinson鈥檚 patients are also convinced
that L-dopa exerts stronger control over their symptoms. 鈥淭o some that
difference will be worth the price in side effects.鈥�