This study will be an open-label, randomized, multi-center, 2-way crossover Pharmacokinetic PK evaluation of a single inhaled dose of CVT-301 84 mg and a single oral dose of carbidopa/levodopa CD/LD 25 mg/100 mg (Sinemet®) under fed conditions in Parkinson's Disease (PD) patients who regularly take CD/LD.

The study duration includes a screening period followed by an overnight stay in the center (4 days, 3 nights) to complete 2 treatments, including a 48-hour interval between the treatments, and a follow-up phone call 1-2 days after discharge from the center.

On each of two treatment days, subjects will consume a standard high fat meal and then receive either (A) a single inhaled dose of CVT-301 or (B) a single dose of oral CD/LD followed by Pharmacokinetic (PK) sampling for 4 hours. A crossover design will be used such that each subject receives both Treatment A and Treatment B over the 2 treatment days, randomized 1:1 to the treatment sequence AB or BA.

Inclusion Criteria:

• Men and women between the ages of 30 and 85 years, inclusive.
• Have idiopathic PD (i.e., not induced by drugs or other diseases) as defined by fulfilling Steps 1 and 2 of the United Kingdom (UK) Brain Bank criteria, diagnosed after the age of 30 years.
• Classified as Stage 1 to 3 (in the ON state) on the modified Hoehn and Yahr scale for staging of PD severity.
• Stable on other non levodopa PD medications for at least 4 weeks prior to the Screening Visit.
• Subjects must have normal cognition as confirmed by a score of ≥ 25 on the Mini Mental State Examination (MMSE), performed in the ON state.
• Forced expiratory volume in one second (FEV1) ≥60% of predicted for race, age, sex, and height and FEV1/FVC (forced vital capacity) ratio ≥70%.
• Body Mass Index (BMI) between 18 - 32 kg/m2, inclusive.

Exclusion Criteria:

• Any flu-like syndrome or other respiratory infections within 2 weeks prior to the Screening Visit.
• Chronic obstructive pulmonary disease (COPD), asthma, or other chronic respiratory disease within the last 5 years.
• History of any cancer in the past 5 years with the exception of successfully treated basal cell carcinoma.
• Narrow angle glaucoma or a history of peptic ulcer disease less than 1 year prior to screening.
• Previous surgery for PD (including but not limited to deep brain stimulation or cell transplantation).
• Current use of nicotine patch or tobacco-containing products including cigarettes, electronic cigarettes, cigars, chewing tobacco, pipe tobacco or snuff or use within 4 weeks prior to the Screening Visit, or expected use during the study.
• Marijuana smoking within 4 weeks prior to the Screening Visit, or expected smoking/inhalation during the study.