About dopamine stimulators
Dopamine stimulators are drugs that mimic the effect of the neurotransmitter dopamine in the brain. Also known as dopamine agonists, these drugs help relieve symptoms of Parkinson’s disease. They also may be used to treat other health concerns, such as tic disorders and certain rare metabolic diseases.
Dopamine is a neurotransmitter that helps regulate body movements and other motor and cognitive functions. Adequate amounts of dopamine in the brain help promote smooth, coordinated movements. Inadequate levels of dopamine triggers symptoms such as tremor, rigidity and bradykinesia (slowness of movement). Dopamine itself is not typically used as a medication because when it is taken orally, it does not cross the blood-brain barrier, and thus cannot be transported into the brain.
In healthy bodies, neurons produce and release dopamine in the brain and other parts of the body. When the dopamine is released by one neuron, it is received by the receptors of the next neuron. This chain reaction eventually leads to the stimulation of nerves.
Dopamine stimulators cause neuron receptors to react as though they are receiving dopamine, even though there is a deficiency of dopamine in the body. This helps to maintain the chain reaction, which would normally have stopped or slowed down because of the absence of dopamine.
Various neurological disorders can interfere with dopamine production and cause levels in the brain to drop. This may lead to the development of a movement disorder. For example, patients with Parkinson’s disease experience a destruction of dopamine-producing cells. This leads to a sharp decline in dopamine production. By the time 80 percent of these cells are depleted, neurons in the brain begin to behave in an abnormal manner, triggering the symptoms of Parkinson’s.
Dopamine stimulators provide relief from movement disorder symptoms while delaying the onset of certain side effects (e.g., dyskinesias). However, dopamine stimulators may not be as effective as other treatment methods for movement disorders. Levodopa therapy – the combination of levodopa (a dopamine precursor) with other medications – is generally recognized as the most effective treatment method for movement disorders such as Parkinson’s disease. However, there are several drawbacks to levodopa therapy that make it unsuitable for some patients. For example, the side effects of levodopa therapy can be severe for some patients. Additionally, most long-term users of levodopa therapy usually experience a wearing-off effect after a period of time. Dopamine stimulators are less likely to involve this wearing-off effect and, therefore, may be more suitable for patients with mild to moderate movement symptoms.
Dopamine stimulators are often taken in combination with levodopa therapy, but may also be taken on their own. They include:
Generic Name Brand Name(s)
Apomorphine is the dopamine stimulator that most closely mimics the effects of dopamine. However, this medication cannot be taken in pill form and must be delivered beneath the skin by injection. It begins working within about 10 minutes of being administered, although its effects last only for about 90 minutes. Thus, it is often used as a “rescue therapy” to quickly alleviate symptoms that flare up in patients with movement disorders. Patients sometimes use apomorphine in this way between doses of levodopa.
Cabergoline (brand: Dostinex) is another dopamine stimulator. It has currently been approved for use in the United States for the treatment of hyperprolactinemia (excess milk production in post-partum women). This drug is currently marketed in Europe and elsewhere as a treatment for Parkinson’s disease, where it is taken in a much higher dosage than required for treatment of hyperprolactinemia. There is significant debate among physicians about whether cabergoline should be used to treat Parkinson’s disease in the United States.
Recently, studies have shown that people who are taking pergolide (brand name Permax) or cabergoline as a treatment for Parkinson’s disease may have an increased risk of developing heart valve defects. In March 2007, pergolide was withdrawn from the market upon request by the Food and Drug Administration (FDA). Patients who are concerned about the risks associated with these medications are advised to consult their physician.
Dopamine stimulators may be used to help reduce the symptoms of a variety of neurologically based movement disorders. These may include:
- Parkinson’s disease
- Multiple system atrophy
- Periodic limb movement disorder
- Restless leg syndrome
There have been a few reports of dopamine stimulators being successfully used in the treatment of tic disorders and certain rare metabolic diseases.
Conditions of concern
Certain health conditions may preclude the use of dopamine stimulators by some patients. These drugs may not be suitable for people with a history of the following:
- Arrhythmia, pericarditis or other heart problems
- Hallucinations, confusion or other psychological disorder
- Pleuritis, pleural effusion or pleural fibrosis
- Retroperitoneal fibrosis
- Toxemia of pregnancy
- Untreated high blood pressure (hypertension)
In addition, dosage levels of dopamine stimulators may have to be adjusted for patients with kidney or liver problems.
Recent studies have shown that two types of dopamine stimulators – pergolide and cabergoline – may increase the risk of heart valve defects in patients taking the medication to treat Parkinson’s disease. Patients who have a history of heart problems or who otherwise have concerns about taking these medications should consult their physician as soon as possible.
- Side effects
Potential side effects
People who take a dopamine stimulator in combination with the dopamine precursor levodopa often experience drowsiness. In some cases, this is severe enough to induce sudden sleep, which may occur without warning. Patients are urged to be aware of this possibility, which is most likely to occur when beginning therapy, increasing dosage level or switching to a new dopamine stimulator.
Because dopamine stimulators can cause drowsiness, patients are urged to avoid certain activities (e.g., driving, using machinery) until they know how these drugs are likely to affect them.
Some patients who take dopamine stimulators also may find themselves more likely to engage in compulsive behaviors, such as hypersexuality, compulsive gambling and compulsive overeating. Patients who experience such symptoms are urged to contact their physician.
Dopamine stimulators may cause additional side effects in patients who take them. These include:
- Abdominal pain
- Chest pain
- Dry mouth
- Nausea and vomiting
- Low blood pressure (hypotension)
- Orthostatic hypotension (low blood pressure resulting from posture change)
- Sleep problems
Some patients who take certain dopamine stimulators (e.g., pergolide, bromocriptine) may be at risk for developing fibrosis, a condition in which excess fibrous connective tissue develops in an organ. However, withdrawal of medication appears to reverse the symptoms of fibrosis for most patients.
Additionally, some patients who take bromocriptine or pergolide may experience inflammatory reactions of the lungs and heart valves. Recent studies have also linked cabergoline with the development of heart valve defects.
Patients who take dopamine stimulators are likely to experience a leveling off of side effects as their body gradually adapts to the drug.
In general, dopamine stimulators are less likely to cause certain side effects (e.g., dyskinesias) than dopamine precursors. This may make dopamine stimulators a more suitable treatment method for people with mild to moderate symptoms.
Drug or other interactions
Certain drugs may interact poorly with dopamine stimulators. As a result, patients are urged to tell their physician if they are taking any of the following types of medications:
- 5HT3 agonists (drugs that mimic the effects of the neurotransmitter serotonin)
- Sedatives and tranquilizers
- How to use
Pregnancy use issues
Experts generally recommend that pregnant women avoid taking medications such as dopamine stimulators. In addition, women who are breastfeeding should avoid use of dopamine stimulators, as some of these medications may be passed through breast milk to children.
Child use issues
Tests have not been performed regarding the effects of dopamine stimulators when used by children. As a result, parents are urged to consult with a physician regarding the benefits and possible risks of using dopamine stimulators in children.
Elderly use issues
Older patients are more likely to experience side effects such as psychosis and edema than younger patients. As a result, many experts recommend that these patients be treated with the dopamine precursor levodopa alone rather than a combination of levodopa and a dopamine stimulator.
Symptoms of medication overdose
Patients or those caring for patients who exhibit any of these symptoms should contact a physician immediately:
- Chest pain
- Heart palpitations or arrhythmias
- Increased dyskinesia
- Involuntary movements
- Loss of consciousness
- Low blood pressure (hypotension)
Questions for your doctorPatients may wish to ask their doctor the following questions related to dopamine stimulators:
- Why do you suggest I take dopamine stimulators to treat my condition?
- What are the alternative treatments available to me?
- Which dopamine stimulator do you believe would be most effective for me?
- What are the side effects associated with this drug?
- Will I have to stop taking other medications while I am on this drug?
- How soon after I start taking this drug should I begin to notice improvement?
- How long will I be required to take this medication?
- What should I do if I miss a dose of my drug?
- If the drug is not effective, can I try another dopamine stimulator?
- Is this drug safe for me if I’m pregnant or breastfeeding?
- Is this drug safe for my child/elderly parent?