Parkinson`s disease (PD) is a common progressive neurodegenerative disorder that is characterized by the loss of striatal dopamine (DA) as a result of the degeneration of dopaminergic (DAergic) neurons in substantial nigra, thus, produces progressive disability. The clinical manifestation of this disease includes resting tumor, rigidity, bradykinesia, and disturbance of posture and pace (1). The main features of PD are trembling (tremor), increased muscle tone (rigidity), slowness of movement (bradykinesia) and disturbance of posture and balance. These manifestations are encountered because of a depletion of the neurotransmitter dopamine due to the progressive loss of nigral neurons in the brain (2-4). There is a general approach followed to the treatment of patients with PD, which is the administration of drugs to assuage the symptoms. One common approach is the restoration of dopamine by administering its precursor levodopa (LD). LD provides immediate and satisfactory control of most symptoms. But, after two to five years of stable response to LD treatment, approximately half of these patients develop motor complications some of which are thought to be highly correlated with prolonged LD exposure (5,6). It is because of the above-mentioned setbacks of the PD therapy using LD new therapeutic approaches have been explored.
Dopamine agonists bypass the degenerating nigral neurons and stimulate the dopamine receptors directly (9, 10). BR monotherapy or a combination of LD and BR as a first-line treatment in early PD is one of the possibilities of treating PD. These treatment strategies would allow either a later start (BR monotherapy) or a lower dose of LD (BR/LD combination therapy), thus potentially preventing or delaying the onset of the late complications of LD therapy. (11,12)
DAergic replacement therapy with the precursor levodopa or agonists, that stimulate the dopamine receptor is effective in ameliorating various signs and symptoms of the early onset of PD. Although, progressive degeneration finally leads to severe motor, mental, and functional disability.