Inclusion Criteria:  Patients diagnosed with Parkinson's Disease as defined by the UK Parkinson's Disease Society Brain Bank Criteria Signed a current IEC approved informed consent form Male or female patients between ages 30-85 years At least three years of prior treatment with levodopa of at least 400 mg daily subject to a maximum of 8 divided doses per day (excluding bedtime and nighttime) Waking day dyskinesia of > 25% determined as a score of ≥2 as per Question 4.1 on the UPDRS Ambulatory or ambulatory-aided (e.g., walker or cane) and able to complete study assessments Have been on stable doses of all anti-Parkinson's medications for 30 days prior to entry into the study, including a levodopa preparation administered not less than three times daily, and be willing to remain on the same doses of medications throughout the course of the study Any other current and allowed prescription/non-prescription medications and/or nutritional supplements taken regularly must have been at a stable dose and regimen for at least 30 days prior to screening, and the patient must be willing to continue the same doses and regimens during study participation. The subject/caregiver must demonstrate the ability to complete an accurate home diary based on training and evaluation (visit 2) Subjects must have available a responsible adult caregiver/companion who will drive the subject home following infusions Female subjects not of childbearing potential Male subjects, regardless of their fertility status, with nonpregnant women of childbearing potential (WOCBP) partners must agree to either remain abstinent (if this is their preferred and usual lifestyle) or use a highly effective (less than 1% failure rate) method of contraception (such as combination oral contraceptives, implanted contraceptives, or intrauterine devices) or effective method of contraception (such as diaphragms with spermicide or cervical sponges) for the duration of the study and until their plasma concentrations are below the level that could result in a relevant potential exposure to a possible fetus, predicted to be 90 days following the last dose of study drug  Exclusion Criteria:  Diagnosis of an atypical or secondary Parkinsonian syndrome Lack of documented response to levodopa Hoehn and Yahr stage of 5 Known prior exposure to ketamine or other NMDA inhibitors within the last 30 days History of neurosurgical intervention related to PD (e.g., deep brain stimulation) History of seizures within two years prior to screening History of transient ischemic attacks or stroke within two years prior to screening History of intracerebral hemorrhage due to hypertension. History of clinically significant arrhythmia or unstable angina within the past five years History of myocardial infarction within 2 years prior to screening History of NYHA Class 3 or 4 heart failure within 2 years prior to screening Aneurysmal vascular disease (e.g., intracranial, thoracic or abdominal aorta) History of hypertensive encephalopathy