First Time Use of SD-809 in Huntington Disease

This is a randomized, double-blind, placebo-controlled, parallel-group study designed to evaluate the efficacy, safety and tolerability of SD-809 for the treatment of chorea associated with Huntington's Disease. Approximately 90 subjects will be randomized (1:1) into the study, with approximately 45 subjects receiving SD-809 and 45 subjects receiving placebo. The study will be conducted at approximately 30 centers in the U.S. and Canada.

Inclusion criteria

• Subject is at least 18 years of age or the age of majority (whichever is older) at Screening.
• Subject has been diagnosed with manifest HD
• Subject is able to swallow study medication whole.
• Female subjects of childbearing potential agree to use an acceptable method of contraception from screening through study completion.
• The subject has a reliable caregiver who interacts with the patient on a daily basis, oversees study drug administration, assures attendance at study visits and participates in evaluations, as required.
• Subject is able to ambulate without assistance for at least 20 yards (Note: The use of assistive devices (i.e., walker, cane) is permitted during ambulation).

Exclusion criteria

• Subject has a serious untreated or under-treated psychiatric illness, such as depression, at Screening or Baseline.
• Subject has active suicidal ideation at Screening or Baseline.
• Subject has history of suicidal behavior at Screening or Baseline:
• Subject has evidence for depression at Screening or Baseline.
• Subject has an unstable or serious medical or psychiatric illness at Screening or Baseline.
• Subject has been recently exposed to tetrabenazine.
• Subject has received any of the following concomitant medications within 30 days of Screening or Baseline:

• Antipsychotics
• Metoclopramide
• Monoamine oxidase inhibitors (MAOI)
• Levodopa or dopamine agonists
• Reserpine
• Amantadine
• Memantine
• Subject has significantly impaired swallowing function at Screening.
• Subject has significantly impaired speaking at Screening.
• Subject requires treatment with drugs known to prolong the QT interval.
• Subject has a prolonged QT interval on 12-lead ECG at Screening.
• Subject has evidence of hepatic impairment at Screening.
• Subject has evidence of significant renal impairment at Screening.
• Subject has known allergy to any of the components of study medication.
• Subject has participated in an investigational drug or device trial within 30 days (or 5 drug half-lives) of Screening, whichever is longer.
• Subject is pregnant or breast-feeding at Screening or Baseline.
• Subject acknowledges present use of illicit drugs at Screening.
• Subject has a history of alcohol or substance abuse in the previous 12 months.