The role of dopamine agonists in early Parkinson's disease.

Recent evidence from clinical studies suggests an expanded role for dopamine agonists as initial dopaminergic monotherapy in the treatment of Parkinson's disease (PD). The rationale for the use of dopamine agonist monotherapy in early disease is to delay the initiation of levodopa or to decrease the total exposure to levodopa, thereby reducing the motor complications of long-term levodopa therapy. Dopamine agonists, when used alone, rarely promote the development of dyskinesias and motor fluctuations that complicate levodopa treatment. Theoretically, there is potential for a neuroprotective effect by decreasing the oxidative breakdown of dopamine and free radical generation. Because they act on postsynaptic dopamine receptors of the striatum, dopamine agonists act independent of the synthetic dopaminergic enzyme system and are not dependent on degenerating presynaptic neurons in the substantia nigra. This article will review the traditional role of dopamine agonists and will focus on emerging strategies for the treatment of PD, including early monotherapy with dopamine agonists and early combination therapy with dopamine agonists and levodopa.