Parkinson's Treatments: Dopamine Agonists

Names:

How They Work:

Dopamine agonists are able to mimic dopamine and stimulate dopaminergic receptors in the brain, allowing the brain to react to the drugs as it would to dopamine. There are three types of dopamine receptors: D1, D2, and D3 receptors, each of which have different and complicated biological roles. These drugs work by either stimulating D1, D2, or D3 separately or through stimulating some combination of the three receptor types. Like L-dopa, these drugs are able to cross the blood-brain barrier (the line of defense by the brain that prevents unwanted chemicals from getting mixed in with its wiring), and reach the dopamine receptors of the brain. Stimulation of these receptors usually decreases the severity of the Parkinson's dyskinesia and tremors.

The effect of each dose of a dopamine agonist stay in the body longer than L-dopa, and therefore can be taken less frequently. The most commonly prescribed versions of these drugs are Bromocriptine and Pergolide, although the most recently approved drugs Pramipexole and Ropinrole are becoming more accepted prescriptively, as well.

These new alternative drugs are usually administered after L-Dopa begins to lose its effectiveness. They both increase "on" time, and allow patients to decrease their L-dopa dosage, which usually improves DID. They are also used along with L-dopa/carbidopa at the beginning of therapy in order to limit the necessary dosage of L-dopa, so that it remains an effective treatment for a longer period of time. According to FDA studies, these drugs have been proven effective in some cases:

Mirapex and Requip, which mimic dopamine's role in the brain, allow patients to regain some of their lost muscle control. Both are approved for use alone or with levodopa drugs. In clinical trials, patients taking Mirapex alone saw as much as a 30 percent improvement in symptoms. Combining Mirapex with levodopa drugs allowed advanced patients to reduce those doses by up to 25 percent. Requip trials showed similar benefits, allowing patients to reduce L-dopa doses by an average of 31 percent.(Henkel 1998)

Similar results were obtained in studies with the drug ropinirole: L-dopa dosing was reduced, the proportion of off episodes to on episodes was decreased (Geriatrics 1998). Reducing L-dopa doses in all cases helped to lessen DID and other side effects associated with L-dopa. However, these improvements were limited to 35% of the subjects tested.

Common Side-Effects:

Unfortunately, although these side-effects are less dramatic than those of L-Dopa, there are some negative effects from taking dopamine agonists:



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