Dopamine is an important neurotransmitter, a chemical that carries nerve signals across the gap between nerve cells in the brain. Dopamine agonists are drugs that bind to dopamine receptors on nerve cells, thereby taking the place of dopamine. The agonists activate the receptor in the same way that dopamine does and have the same neurotransmitter effects as dopamine. Scientists have discovered that certain dopamine agonists can be of value in the treatment of depression.
The Facts
In the December 2004 issue of "The Psychiatrist," Dr. Eromona Whiskey at Maudsley Hospital in London, England, and her colleague review the scientific literature on the use of the dopamine agonist pramipexole for the treatment of depression. Whiskey reports that pramipexole has been used as an adjunct therapy in cases of refractory depression in which patients have been using conventional antidepressants without much success. In these instances, 40 to 50 percent of patients respond favorably to the addition of pramipexole to the treatment regimen. In the May 2005 issue of the "Canadian Journal of Psychiatry," Dr. Paolo Cassano and his team at the Massachusetts General Hospital discuss the role of the dopamine agonist ropinirole as an adjunct therapy for patients with treatment-resistant depression. Patients in Cassano's study had either major depressive disorder or bipolar depression, and were taking standard prescription antidepressants to little or no avail. Cassano found that adding a daily dose of ropinirole to the standard treatment led to a favorable response for 40 percent of the patients after 16 weeks.
Depression in Parkinson's Disease
Depression is common among patients who have Parkinson's disease. It is well known that dopamine agonists can treat the motor function problems of Parkinson's disease, but recent research by Dr. Paolo Barone of the University of Naples and published in the June 2010 issue of "The Lancet Neurology" demonstrates that pramipexole can treat not only motor function problems but also depression symptoms in patients with Parkinson's disease.
Benefits
In the September 2008 issue of the "European Jounal of Neurology," Dr. Matthias R. Lemke of the University of Kiel in Germany points out two advantages to the fact that a dopamine agonist can address both depression symptoms and motor function problems in Parkinson's disease patients. First, patients do not have to worry about side effects of antidepressant drugs and second, drug-drug interactions become less likely.
Considerations
Further study and research on the use of dopamine agonists for the treatment of major depression are necessary to increase doctors' understanding of their clinical effects. For example, experiments to establish a dose response relationship must be executed. Pramipexole may serve as an adjunct therapy in patients with treatment-resistant depression, but it is premature to recommend it for routine use in depressed patients.
Warnings
With pramipexole, nausea is a dose-limiting side effect in the treatment of depressed patients. In the study of ropinirole for patients with treatment-resistant depression, two of the 10 patients dropped out because of dizziness caused by the drug.
References
- Addiction Science Research and Information Center: The University of Texas: Dopamine--A Sample Neurotransmitter
- "The Psychiatrist"; Pramipexole in Unipolar and Bipolar Depression; Eromona Whiskey et al.; December 2004
- "Canadian Journal of Psychiatry"; Ropinirole in Treatment-resistant Depression: A 16-week Pilot Study; P. Cassano, et al.; May 2005
- MedlinePlus: Ropinirole
- "The Lancet Neurology"; Pramipexole for the Treatment of Depressive Symptoms in Patients with Parkinson's Disease: A Randomised, Double-blind, Placebo-controlled Trial; Paolo Barone et al.; June 2010
- "European Journal of Neurology": Dopamine Agonists in the Treatment of Non-motor Symptoms of Parkinson's Disease: Depression; MR Lemke; September 2008
