(+)-Alpha-Dihydrotetrabenazine Phase I

This research study is intended to determine the initial safety and tolerability of single
oral doses of the drug (+)-alpha-dihydrotetrabenaxine (HTBZ) in normal volunteers. HTBZ is
believed to be the active ingredient in the FDA-approved drug tetrabenazine (TBZ, brand name
Xenazine), prescribed for treatment of involuntary movements in patients with Huntington's
chorea. TBZ is a mixture of closely-related compounds (isomers) and is readily metabolized
(converted) in the human body to HTBZ and related isomers. Investigators believe that HTBZ,
the drug to be studied in this research, is the active ingredient in TBZ. The present study
will confirm safety and tolerability of HTBZ and will investigate its expected effects on
brain sites that are the target of TBZ therapy.