Treating Bacterial Overgrowth in Parkinson's Disease

Inclusion Criteria: * Diagnosis of idiopathic PD * Daily "off" time ≥ 4 hours * No changes in levodopa or any other dopaminergic medications expected during the course of the study * Will be screened for cognitive ability (Montreal Cognitive Assessment score of ≥ 24) prior to enrollment * Will be screened for presence of SIBO prior to enrollment Exclusion Criteria: * Any comorbid non-PD-associated gastrointestinal (e.g., achlorhydria) or systemic diseases that may alter absorption or confound the study results * Exposure to proton pump inhibitors, immunosuppressive drugs, medications that affect GI motility (such as prokinetics, anticholinergics, and tricyclic antidepressants), antibiotics or any other drugs that affect the intestinal flora (such as laxatives) within a month prior to enrollment. * Prior deep brain stimulation or ablative functional neurosurgery. * Prior allergy to rifaximin * Women who are pregnant, lactating, or plan to become pregnant.