This is a randomized, open-label, rater-blinded, multicenter, 3-treatment, 3 period, single-dose crossover study. Approximately 51 qualified immediate-release (IR) CD-LD-experienced advanced Parkinson's disease patients will be randomized to 1 of 3 dosing sequences.

Objectives:

• Assess the pharmacodynamics and pharmacokinetics (PK) of IPX203 (carbidopa and levodopa) in subjects with advanced Parkinson's disease.
• Characterize the safety of IPX203 in subjects with advanced Parkinson's disease.

IPX203 contains two different drugs called levodopa and carbidopa in one capsule.

• levodopa turns into a material called 'dopamine' in your brain. The dopamine helps to improve the symptoms of your Parkinson's disease.
• carbidopa belongs to a group of medicines called 'aromatic amino acid decarboxylase inhibitors'. It helps levodopa work more effectively by slowing the speed at which levodopa is broken down in your body.

Inclusion Criteria:

Male or female subjects diagnosed with idiopathic PD with motor complications, who are currently being treated chronically with stable regimens of CD-LD.

Requiring at least 400 mg but not more than 1600 mg LD per day during the waking hours; and at least 100 mg but not more than 250 mg LD from IR CD-LD for the first morning dose.

Dosing frequency of IR CD-LD of at least 4 times daily excluding nighttime dosing.

Have an average of at least 2 hours per day "off" time during the waking hours and at least 1 hour "off" time per day, based on the PD diary collected for 3 consecutive days prior to Visit 1.

Exclusion criteria:

Have used first morning dose of controlled-release (CR) CD-LD or Rytary for at least 4 weeks prior to Visit 1.

Female subjects who are currently breastfeeding or lactating.

Had prior functional neurosurgical treatment for PD (ablation or deep brain stimulation) or if such procedure(s) are planned or anticipated during the study period.

Allergic to study drugs

History of medical conditions or of a prior surgical procedure that would interfere with LD absorption, such as gastrectomy or small-bowel resection.

History of peptic ulcer disease or upper gastrointestinal hemorrhage.

History of narrow angle glaucoma.

History of myocardial infarction with residual atrial, nodal, or ventricular arrhythmias; neuroleptic malignant syndrome; or nontraumatic rhabdomyolysis.

History of psychosis.

Employees or family members of the Investigator, study site, or Sponsor.

Subjects who, in the opinion of the clinical investigator, should not participate in the study.

Based on clinical assessment, subject does not adequately comprehend the terminology needed to complete the PD diary.