A Study to Assess the PK and Pharmacodynamics of IPX203 in Subjects With Advanced Parkinson's Disease

Eligibility will be determined at screening and Visit 1 of the study. Inclusion Criteria: * Diagnosed with idiopathic PD at age ≥ 40 years who are being chronically treated with stable regimens of CD-LD but experiencing motor complications. * Hoehn and Yahr Stages 2, 3, or 4 * Montreal Cognitive Assessment (MoCA) score ≥ 24 at Screening Visit in "on" state. * For the 4 weeks prior to the Screening, the subject experiences daily "wearing-off" episodes with periods of bradykinesia and rigidity and experiences an "off" state upon awakening on most mornings by history. * Responsive to CD-LD therapy and currently being treated on a stable regimen with CD-LD for at least 4 weeks prior to Visit 1 * Typically experiences an "on" response with the first dose of IR CD-LD of the day (by subject history). * By history, efficacy of the first morning dose of IR CD-LD lasts less than 4 hours Exclusion Criteria: * History of medical conditions or of a prior surgical procedure that would interfere with LD absorption, such as gastrectomy or proximal small-bowel resection. * Liver enzyme values ≥ 2.5 x the upper limit of normal; or history of severe hepatic impairment. * History of drug or alcohol abuse within the 12 months prior to Screening. * Received within 4 weeks of Visit 1 or planning to take during participation in the clinical study: any doses of a controlled-release (CR) LD apart from a single daily bedtime dose or any doses of Rytary, additional CD (eg, Lodosyn) or benserazide (eg, Serazide), or catechol-O-methyl transferase inhibitors (entacapone or tolcapone) or medications containing these inhibitors (Stalevo). Received within 4 weeks of Visit 1 or planning to take during participation in the clinical study: nonselective monoamine oxidase (MAO) inhibitors, apomorphine, or dopaminergic blocking agents including antiemetics. * History of psychosis within the past 10 years. * Treatment with any dopamine antagonist antipsychotics for the purposes of psychosis or bipolar disorder within the last 2 years. * Based on clinical assessment, subject does not adequately comprehend the terminology needed to complete the PD Diary.