Department of Neurology
Dopamine Agonists in Parkinson’s Disease
Information for Patients
What are Dopamine Agonists?
Dopamine Agonists are medications used to treat Parkinson’s disease. There are several different types, Bromocriptine (Parlodel), Cabergoline (Cabaser), Pergolide (Celance), Pramipexole (Mirapexin) and Ropinirole (Requip).
How Do They Work?
In Parkinson’s disease there is a deficiency in a substance called dopamine in the base of the brain. Dopamine agonists are synthetic compounds which stimulate the brain in a similar way to dopamine, thus in effect are doing the job that the dopamine normally does.
When Should Treatment Be Started?
Treatment is started when symptoms become troublesome. If you can manage without treatment there is no advantage in starting treatment early. Low doses are used first and gradually increased over months and years. The reason for delaying treatment until it is necessary is to gain time and delay the onset of troublesome side effects in years to come.
Which Symptoms Will The Dopamine Agonist Help?
Parkinson’s disease has 3 main symptoms namely tremor (or shaking), stiffness of the muscles and slowness. The dopamine agonists help symptoms of slowness and stiffness. The tremor may also be helped, but generally speaking the tremor unfortunately does not respond all that well to any of the Parkinson’s disease treatments.
Are There Side Effects From The Treatments?
Nausea and light headedness may occur when starting the medication in about ¼ of patients. Usually this is mild and settles as your body gets used to the medication. If these side effects are more severe an anti-sickness tablet is available from your G.P. (Domperidone or Motilium 10mg. up to 3 times per day, occasionally increased to 20mg. up to 3 times per day). Confusion and hallucinations can also be a side effect. The hallucinations tend to be visual and take the form of you seeing things that are not there.
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These tend to be dose related and settle when the dose is reduced or stopped. Sudden onset of sleep during daily activities has been reported in some cases. If you develop this side effect you must not drive or operate machinery. Ankle swelling can also occur.
Some of the dopamine agonists have other side effects. Pergolide (Celance), Bromocriptine (Parlodel) and Cabergoline (Cabaser) can cause a rare but potentially serious side effect of fibrous tissue or excess fluid forming around the lungs or the heart. The medication is stopped if this occurs. If you are on these preparations you will be monitored for early signs of these side effects with blood tests and chest X-rays. Pramipexole (Mirapexin) and Ropinirole (Requip) do not cause these side effects as they are made from a different formulation.
What Alternatives are Available?
The main alternative to a dopamine agonist is a levodopa preparation. The names are Sinemet and Madopar. Levodopa is converted in the brain to dopamine and replaces the dopamine which is lacking. The levodopa in these tablets is combined with another substance which helps concentrate the dopamine in the base of the brain where it is needed.
Levodopa is more effective than the dopamine agonist in helping the symptoms of Parkinson’s disease. However, after being on this type of medication for a number of years troublesome side effects can occur. These are involuntary movements which you cannot control (dyskinesias), wearing off effects of the medication and unpredictable effects such as freezing (stiffening up completely) which is called the “on” / “off” effect. These side effects are less common with the dopamine agonists. For this reason, the dopamine agonists are often started first, the dose gradually increased to a maximum level, then the dopamine preparations (“levodopa”) added when more treatment is required. The choice depends on the severity of your symptoms and any other health problems or treatments you may have.