Types of Dopamine Agonists

Dopamine is a chemical that acts as a neurotransmitter in the central nervous system, affecting the brain's ability to control movement and emotional response. Dopamine agonists are drugs that mimic the action of dopamine, binding to dopamine receptors and causing the neurons in the brain to respond as if dopamine were present.



Doctors prescribe dopamine agonists for a number of conditions, including Parkinson's disease, restless leg syndrome, tardive dyskinesia and certain endocrine disorders.

Oral: Ergoline

• The ergoline dopamine agonists are bromocriptine, sold under the brand name Parlodel, and cabergoline, sold as Dostinex. These medications are derived from ergot alkaloids produced by Claviceps purpurea, a common fungus.

  In addition to mimicking the effects of dopamine, these medications also block the release of prolactin, a hormone produced in the pituitary gland, which makes them a beneficial treatment for some endocrine disorders.

Oral: Non-Ergoline

• The non-ergoline dopamine agonists include pramipexole, sold as Mirapex, and ropinirole, sold as Requip. Approved by the FDA in 1997, these drugs treat early motor symptoms of Parkinson's disease, and play an important role in controlling motor difficulties. They are also a common treatment for restless leg syndrome.

Oral: Extended Release

• The non-ergoline dopamine agonists are also available in extended-release form. Extended-release pramipexole is sold as Mirapex ER, and extended-release ropinirole is sold as Requip XL. This formulation releases the active ingredients into the bloodstream at a gradual and steady pace, creating a sustained, stable therapy without the peaks and valleys of the shorter-acting formulas. A further advantage is that instead of taking three or four pills a day, patients can take one pill, once a day.

Transdermal

• In 1997, the FDA approved a transdermal delivery system for the medication rotigotine. Sold under the brand name Neupro, it offered stable, continuous delivery of the dopamine-mimicking medication from a patch affixed to the patient's skin.

  In 2008, however, UCB, the drug's manufacturer, recalled the patches in the U.S. and some European markets, because the rotigotine had a tendency to crystallize on the patches. The company felt this could make less of the drug available for absorption through the skin, thereby reducing its effectiveness.

  The transdermal patches are still available in Europe, but according to a press release, the FDA has advised UCB to reformulate the product for the U.S. market.

Injection

• Apomorphine is an injectable dopamine agonist. It was first used to treat Parkinson's disease in the 1950s, but it caused excessive side effects like nausea and vomiting. The injectable form of apomorphine was introduced in the 1990s, and found success as a "rescue" therapy.

  Because it works quickly and can be injected up to five times a day, apomorphine is especially helpful when Parkinson's patients experience episodes of "stuck" or "frozen" muscles, which result in immobility and the inability to perform daily activities.