Study of the Effects of Dopaminergic Medications on Dopamine Transporter Density in Subjects With Parkinson's Disease

A Single-blinded Assessment of the Short-term Effects of Cabergoline vs. Carbidopa/Levodopa on SPECT Dopamine Transporter Density in Out-patient Subjects With Parkinson's Disease

This study investigates whether there is a change in 123iodine-2ß- carbomethoxy-3ß-(4-iodophenyl) tropane ([123I]ß-CIT) uptake after short-term treatment with levodopa compared to either dopamine agonist or placebo.

This is a multi-center, open-label study of short-term treatment with levodopa or cabergoline on striatal DATscan uptake in early Parkinson's disease. Approximately 120 Parkinson's disease subjects will be randomized to receive either carbidopa/levodopa, cabergoline or no treatment during a twelve week period. Subjects will undergo SPECT imaging with DATscan at screening and after 12 weeks. After twelve weeks carbidopa/levodopa and cabergoline treatment will be withdrawn and all subjects will undergo SPECT imaging with DATscan after 8 weeks (20 weeks after baseline).

Inclusion Criteria:

• The subject is aged 40 years or older.
• Written informed consent is obtained.
• Subjects have a clinical diagnosis of idiopathic Parkinson's disease.
• Hoehn and Yahr stages for subjects are I-II.

Exclusion Criteria:

• The subject has atypical or drug-induced Parkinson's disease.
• The subject has dementia.
• The subject has clinically significant abnormal laboratory values, and/or clinically significant or unstable medical or psychiatric illness.
• The subject is pregnant.