Dihydrotetrabenazine or DTBZ is an organic compound with the chemical formula C<sub>19</sub>H<sub>29</sub>NO<sub>3</sub>. It is a close analog of tetrabenazine. DTBZ and its derivatives, when labeled with positron emitting isotopes such as carbon-11 and fluorine-18, are used as PET radioligands for examining VMAT2.
[<sup>11</sup>C]DTBZ as a PET radioligand with affinity for VMAT2 was developed in the mid 1990s by David E. Kuhl and colleagues at the University of Michigan. There are two enantiomers of alpha-dihydrotetrabenazine, and the dextrorotary(or (+) isomer) has a high affinity of about 1 nanomolar K<sub>i</sub> whereas the levorotary (or (-) isomer) has approximately 1000 fold lower affinity with a K<sub>i</sub> of about 2 micromolar.
VMAT2 is a membrane bound protein and a biomarker for Parkinson's disease. Binding of DTBZ to VMAT2 in individuals with Parkinson's disease is significantly reduced. Moreover, the VMAT2 density as determined by [<sup>18</sup>F]DTBZ has been shown to be well, inversely correlated with the severity of Parkinson's disease.
Avid Radiopharmaceuticals has sponsored clinical trials of [<sup>18</sup>F]AV-133 (or [<sup>18</sup>F]Fluoropropyl-(+)-DTBZ) to identify subjects with dopaminergic degeneration.