Dopamine agonists have been used to treat Parkinson's disease (PD) since the late 1970s (1). These agents were initially introduced as adjunctive therapy to levodopa. In the last 30 years, dopamine agonists have demonstrated therapeutic benefit in all stages of PD, both in combination with levodopa and as monotherapy. Clinical, neuroimaging, animal, and cellular data suggest not only a levodopa-sparing effect and a delay in the incidence of motor fluctuations, but also a potential neuroprotective effect (2-5). A number of hypotheses have been proposed including a reduction of free radical formation by limiting levodopa exposure or an increase in the activity of radical-scavenging systems, perhaps by changing mitochondrial membrane potential. In addition, some investigators suggest that dopamine agonists may provide neurotrophic activity. However, there is currently no definitive evidence of disease modification beyond the delay of levodopa-induced motor complications.
This chapter reviews the history of dopamine agonists in the treatment of PD and provides a summary of data concerning efficacy, treatment approaches, and comparisons between commonly prescribed dopamine agonists. Similarly designed clinical trials will be discussed, including direct comparative trials, in an effort to better define the relative efficacies of these agents.
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