What Are Dopamine Agonists?
Dopamine agonists are a class of medications that are used to treat the symptoms of Parkinson’s disease (PD). While carbidopa-levodopa therapy is the most effective medication available to treat the motor symptoms of PD, in some cases, other medications, such as dopamine agonists may be used first to avoid some of the side effects seen with levodopa-carbidopa therapy. These medications also be used in conjunction with carbidopa-levodopa therapy.1
Dopamine agonists have demonstrated effectiveness in reducing the motor fluctuations seen in many people with PD. People treated with carbidopa-levodopa with fluctuating symptoms of PD are described as having “on” and “off” episodes. “On” episodes are experienced when medication is working and symptoms are minimal, and “off” episodes are when the medication hasn’t yet taken effect or is wearing off and symptoms are worsened. “Off” episodes can interfere with daily activities and may be experienced multiple times a day. They may last a few minutes or as long as a few hours.1,2
How dopamine agonists work
Symptoms of PD, particularly the motor symptoms, are related to a depletion of dopamine in the brain. Dopamine is the neurotransmitter, or chemical messenger, that is responsible for producing smooth, purposeful movement. Giving dopamine as a treatment is ineffective, as it cannot cross the blood-brain barrier.3
Dopamine agonists mimic dopamine. They bind to proteins on the neurons called dopamine receptors. There are several types of dopamine receptors and particular subtypes are more involved in movement. The dopamine agonists can be designed by chemists to bind to and activate particular dopamine receptors on neurons. Dopamine receptor activation provides relief from symptoms of PD, particularly the motor symptoms such as tremor, rigidity, impaired balance, and loss of spontaneous movement.3
Formulations of dopamine agonists
There are several different formulations of dopamine agonists, including:
- Apokyn™ (apomorphine hydrochloride)
- Parlodel® (bromocriptine)
- Neupro® (rotigotine transdermal system)
- Mirapex® (pramipexole dihydrochloride)
- Mirapex ER® (pramipexole dihydrochloride) extended-release tablets
- Requip® (ropinirole)
- Requip® XL™ (ropinirole) extended-release tablets3
- Cabergoline® (off label for Parkinson's disease)
- Kynmobi® (apomorphine hydrochloride)
There are different dosages for each of these formulations, and people with PD may be prescribed different dosages at different points in their disease to manage their symptoms.
Side effects of dopamine agonists
Each medication has its own set of possible side effects, however there are some common side effects that are seen among all dopamine agonists. Common side effects experienced by people taking dopamine agonists include nausea, hallucinations (seeing or hearing things that are not real), sudden sleepiness (also called sleep attacks), and dizziness or light-headedness.
Dopamine agonists may also cause dyskinesia, or sudden and uncontrollable movements. Although dopamine agonists are less likely to cause dyskinesia than carbidopa-levodopa therapy, dyskinesias can greatly affect a person’s quality of life. Another side effect that dopamine agonists may cause is impulse control behaviors, such as increased gambling urges, increased sexual urges, or other intense urges.3,4 Note that these are not all the possible side effects of dopamine agonists. Patients should talk to their doctor about what to expect with treatment with dopamine agonists.
It is important for people with PD to see a movement disorders specialist who is trained in the use of these drugs for PD. Movement disorders specialists understand the interactions of these drugs and how some medications may make symptoms worse. It is also important to talk with your healthcare provider before starting or stopping any new treatments, including over-the-counter medications and alternative treatments.
Besides dopamine agonists, there are several different types of treatment for the symptoms of PD, including carbidopa-levodopa therapy, monoamine oxidase-B (MAO-B) inhibitors, and surgery for deep brain stimulation. Each person with PD experiences a highly individual set of symptoms and progression of the disease. Treatments are determined based on the individual’s symptoms and how they respond to different medications.1