Parkinson's disease

Dopamine receptor agonists: medication for Parkinson’s disease

The main alternatives to levodopa in treating Parkinson’s disease are the dopamine receptor agonists (dopamine agonists). These drugs act directly on the dopamine receptors in the brain, taking the place of the dopamine which the brain cells can no longer produce. They may be used alone or together with levodopa. When used alone, the overall improvement in motor performance is usually less than when combined with levodopa.

Dopamine agonists have the advantage of causing fewer long term motor complications. When they are used together with levodopa, less levodopa is needed which also diminishes the risk of developing side effects, particularly dyskinesia. Dyskinesia is the name given to involuntary movements that can mean that people's bodies distort or their arms or legs jerk uncontrollably. In the past, dyskinesia was almost inevitable after prolonged use of levodopa. 'On/off' effects are much less marked with the dopamine agonists than with levodopa so that symptoms are less likely to appear if a dose is taken a bit late.
A range of dopamine agonists are available and most come as tablets or capsules of various strengths, although some come as patches or injections. People may need to experiment with their doctor to find what works best for them. Patches are handy for some people, but Kevin found the dose from a patch was not enough for him. Brian found it helpful to have his injection delivered by a pump, to help keep a stable level of the drug in his system. He could give himself a booster dose if he needed a bit more to help get him through an event e.g. a party.
The dopamine agonists are not without their own side effects, both in the short and long term, so their use must be carefully monitored.
Since the introduction of dopamine agonists it has been commonly (though not universally) believed that it was wise to start medication with this group of drugs in order to delay the use of levodopa as long as possible. Using a dopamine agonist might not control symptoms quite so well as levodopa, but many neurologists preder to use it as the first treatment in the early stages, particularly for people with young-onset Parkinson’s disease in whom prolonged use of levodopa might result in dyskinesia later.
Dopamine agonists should be introduced gradually, starting with very tiny doses and building up to an effective dose over weeks or even months. People did not notice the sudden and amazing effects observed on first taking levodopa (see Levodopa). The PD symptoms did not improve immediately and often side effects such as nausea and excessive daytime sleepiness were distressing.
The main reason for keeping the dose of medication as low as possible is that the higher the dose, the greater the side effects. Nausea is common and can usually be counteracted with a drug called domperidone. Brian found that since he has been on apomorphine he sometimes vomits unexpectedly without feeling nausea. For more information on apomorphine see Parkinson’s UK.
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Sleepiness is the other symptom which most of the people taking dopamine agonists mention. Some people complained of feeling generally sleepy most of the time though not necessarily falling asleep. Angela was once prescribed too high a dose of ropinirole and said it turned her into a ‘zombie’. Back on a lower dose she still found herself falling asleep in the theatre if she went out in the evening. Others said they would fall asleep suddenly and unexpectedly.
Some people found that although their dopamine agonist made them sleepy they also suffered insomnia at night; several people described waking around 4am, often hungry and restless, sometimes using the time to catch up on work on their computer.
One group of dopamine agonists (cabergoline and pergolide) are derived from ergot and have been associated with fibrotic (scarring) reactions affecting the lungs and the heart. These drugs are still occasionally used but require careful monitoring. Andrew who had two Deep Brain Stimulation operations and was still having severe problems with walking and talking was put on cabergoline 7 years ago; it has helped him and he has had no problems with it.
Very worrying, though rare, side effects of dopamine agonists appear as neuropsychiatric disturbances.
All current information about dopamine agonists mentions possible side effects such as; hallucinations, confusion, pathological gambling, increased libido and hypersexuality as possible side effects. Some also mention other behavioural changes such as an increase in appetite or binge eating, and the urge to buy or shop. The possibility that one of these problems might occur is not regarded as a reason for avoiding these drugs, which are valuable in the long-term management of Parkinson’s disease. But they should not be forgotten. David who developed problems on two different dopamine agonists expressed concern that he himself had little insight into his problem at the time. Helen’s compulsive gambling had occurred while she was using rotigotine patches and disappeared as soon as she was changed back to Sinemet. Gina’s occurred when she was on ropinirole (see Mental disturbances: depression, hallucinations and compulsive behaviour). Parkinsons UK have more information about Parkinson’s drugs and impulsive and compulsive behaviour.

Last reviewed May 2017.
Last updated May 2017.


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