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The dopamine agonists, pramipexole (Mirapex) and ropinirole (Requip), are drugs that are used to treat symptoms of Parkinson's disease. However, these drugs can induce bothersome leg swelling or edema in about 20 percent of patients. The cause of this edema is unknown but may be secondary to stimulation of peripheral dopamine receptors in the kidney or blood vessels. We hypothesise that a peripherally acting dopamine receptor antagonist, will reduce edema in PD patients. This study will assess the effect of the peripheral acting dopamine D2 receptor antagonist, domperidone as a potential treatment for dopamine agonist-induced leg swelling.

The study is a phase II, randomised double-blind, placebo-controlled, cross-over trial. There are four periods: recruitment and randomisation; treatment period one (4 weeks); washout (1 week); and finally treatment period two (4 weeks). Patients will be randomly assigned domperidone 20 mg tid in treatment period one followed by placebo tid in treatment period two, or placebo tid in treatment period one followed by domperidone 20 mg tid in treatment period two.

Inclusion Criteria:

• Idiopathic PD
• On a stable medication regimen for at least one month with leg edema occurring after the start of pramipexole or ropinirole and the absence of other possible reasons for discontinuation of pramipexole or ropinirole treatment (e.g. other adverse effects).

Exclusion Criteria:

• Pregnancy
• Breastfeeding
• Women of child bearing age not using a reliable method of contraception
• Coronary disease, abnormal QT interval on electrocardiogram (EKG)
• Diabetes mellitus
• Hepatic disease
• Alcohol abuse
• Renal disease
• Edema of one leg only
• Presence of other conditions possibly causing leg edema