Dopamine Agonists for Parkinson's Disease

Why They are Used

Dopamine agonists may be used alone to reduce symptoms in the early stages of Parkinson's disease.^[1] This is the current recommended approach for many people newly diagnosed with the disease (especially those under age 60) because it can delay the need for levodopa and thus postpone the motor fluctuations that may occur with long-term levodopa therapy.

A dopamine agonist may be added to treatment with levodopa for advanced Parkinson's disease when:^[1,2]

• Levodopa no longer is able to adequately control symptoms on its own, and increasing the dose to provide adequate control of symptoms would cause excessive side effects.
• Severe motor fluctuations are occurring in a person taking levodopa.

How They Work

Dopamine agonists directly stimulate the nerves in the brain that normally would be stimulated by dopamine. Unlike levodopa, a dopamine agonist is not changed (converted) into dopamine when it enters the body, but it behaves like dopamine.

How Well They Work

When used alone in early Parkinson's disease, dopamine agonists may reduce symptoms of the disease, especially those affecting motor function, such as stiffness and slowness. Although they are not as effective as levodopa in controlling symptoms, they have the benefit of postponing the need for levodopa therapy for up to several years, which in turn may help delay the onset of levodopa-related motor fluctuations.^[3]

When taken in combination with levodopa, dopamine agonists may:^[4]

• Reduce the amount of levodopa needed to control symptoms, thereby reducing some side effects of levodopa
• Improve motor function during both "on" and "off" periods
• Reduce involuntary movements (dyskinesias) associated with long-term levodopa therapy
• Prolong the effect of levodopa and reduce motor fluctuations that occur as a result of the wearing-off effect of levodopa, when the effects of a dose do not last as long as they once did

Some Typical Agonists:

• bromocriptine mesylate (Parlodel)
• pergolide mesylate (Permax)
• pramipexole (Mirapex)
• ropinirole hydrochloride (Requip)

Possible Side Effects

The most common side effects of dopamine agonists include:

• Nausea and vomiting
• Dizziness or fainting
• Sudden, unpredictable attacks of sleepiness. These can be very dangerous if they occur while a person is driving
• Low blood pressure when the person stands up or sits down (orthostatic hypotension)
• Confusion or hallucinations (seeing or hearing things that aren't really there)
• Depression
• Inability to fall or stay asleep (insomnia)
• Jerky involuntary movements (dyskinesias). These may fade once the levodopa dosage is reduced
• Irregular heart rate and chest pain

What To Think About

When used alone, the dopamine agonists are less effective in controlling symptoms than levodopa and often need to be increased slowly over time. These medications can cause side effects, especially sleepiness and hallucinations. Dopamine agonists tend to cause more side effects than levodopa does.

Increasing numbers of doctors are using dopamine agonists as initial therapy in people with newly diagnosed Parkinson's disease in order to delay treatment with levodopa. The American Academy of Neurology now recommends this approach for most people with the disease. In theory, the purpose behind delaying treatment with levodopa, especially in younger people with Parkinson's, is to delay the motor fluctuations that eventually occur with long-term levodopa therapy. However, these motor fluctuations may also occur with the dopamine agonists alone. If a dopamine agonist is used as initial therapy, levodopa may be added when the dopamine agonist is no longer able to control symptoms adequately on its own.^[1]

Pramipexole (Mirapex) and ropinirole (Requip) are among the newer dopamine agonists and may cause fewer side effects than the older dopamine agonists (bromocriptine and pergolide). These newer medications are also more expensive.