Study to Assess the Clinical Benefit and Safety of Droxidopa in Parkinson's Disease

Inclusion Criteria:

- Diagnosed with probable levodopa-responsive idiopathic PD (meeting United Kingdom PD
Brain Bank diagnostic criteria), and receiving levodopa therapy for this disorder.
Other PD medications can also be used

- At least 3 months incidence of typical freezing of gait symptoms, occurring while
levodopa is otherwise providing an "on" mobility state (including at least one of the
following Freezing of Gait patterns: start hesitancy, freezing at making turns or
when passing through a doorway, spontaneous freezing during continued walking, or
Freezing of Gait related to a simultaneous mental or physical activity)

- Have a screening score between 22 and 26 (inclusive) on the Montreal Cognitive
Assessment

- Provide written informed consent to participate in the study

Exclusion Criteria:

- Taking direct acting vasoconstriction agent (i.e. ephedrine or midodrine). Subjects
taking vasoconstrictor agents such as ephedrine or midodrine must stop taking these
drugs at least 2 days or 5 half-lives (whichever is longer) prior to their baseline
visit

- Taking anti-hypertensive medication for the treatment of hypertension.
Anti-hypertensive medication taken at night to prevent supine hypertension will be
allowed

- Changing dose or frequency of PD medication within 2 weeks of baseline

- Use of cognitive-enhancing medications (donepezil, galantamine, rivastigmine,
tacrine, or memantine), catechol-O-methyltransferase inhibitors (tolcapone or
entacapone), anticholinergic drugs, or antipsychotic drugs (including quetiapine or
clozapine).

- Known or suspected alcohol or substance abuse within 1 year (e.g. DSM-IV definition
of alcoholism)

- Past or current history of chronic severe hypertension (with repeated findings of BP
150/100 mmHg in the supine or standing position)

- Symptomatic coronary artery disease, severe congestive heart failure (NYHA Class 3 or
4)

- Unable to remain off any effective Freezing of Gait medications for 12 hrs prior to
Evaluation visits)

- Women who are pregnant, lactating, or plan to become pregnant during the course of
this study

- Women of child bearing potential who are not using two methods of contraception (at
least one barrier, i.e. condom) with their partner.

- Male subjects who are sexually active with a woman of child bearing potential and not
using two methods of contraception (at least one barrier, for example, condom)

- A history of closed angle glaucoma;

- Active (in the last 6 months) atrial fibrillation or, in the investigator's opinion,
any other significant cardiac arrhythmia that should preclude the subject from this
trial

- History of myocardial infarction or unstable angina

- Congestive heart failure (NYHA Class 3 or 4)

- Diabetes insipidus, insulin-dependent diabetes mellitus, or diabetic neuropathy

- In the investigator's opinion, any other significant systemic illness

- Known or suspected malignancy (other than basal cell carcinoma)

- Known gastrointestinal illness or other gastrointestinal disorder that may, in the
investigator's opinion, affect the absorption of study drug

- Any major surgical procedure within 30 days of the baseline visit

- Currently receiving any investigational drug or have received an investigational drug
within 30 days of the baseline visit

- In the investigator's opinion, clinically significant abnormalities on clinical
examination or laboratory testing that should preclude the subject from this trial.

- Findings from suicidality screening that are compatible with risk for suicide