Tetrabenazine

Tetrabenazine is a drug for the symptomatical treatment of hyperkinetic movement disorder and is marketed under the trade names Nitoman® in Canada and Xenazine® in New Zealand and some parts of Europe, and is also available in the USA as an orphan drug. On December 6, 2007 an advisory committee to the U.S. Food and Drug Administration (FDA) voted unanimously to recommend the approval of tetrabenazine, which would be the first drug approved in the United States to treat chorea associated with Huntington disease (HD). The compound is known since the 1950s. Tetrabenazine works mainly as a VMAT-inhibitor^[1] and as such promotes the early metabolic degradation of the neurotransmitter dopamine.

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Common uses

Tetrabenazine is used as a treatment, but not a cure for hyperkinetic disorders^[2] such as:

• Huntington's Disease - specificially the chorea associated with it
• Tourette's Syndrome and other tic disorders
• Tardive dyskinesia, a serious and sometimes irreversible side effect of long-term use of many antipsychotics, mainly typical antipsychotics
• Hemiballismus, spontaneous flinging limb movements due to subthalamic nucleus damage

Side effects

Because tetrabenazine is closely related to the antipsychotics, many of its side effects are similar. Some of these include:

• Akathisia (aka "restless pacing" - an inability to keep still, with intense anxiety when forced to do so)
• Depression - the most common side effect, reported in roughly 15% of those who take the medication
• Dizziness/drowsiness
• Parkinsonism

Unlike many of the antipychotics, tetrabenazine is not known to cause Tardive dyskinesia, and in fact can be an effective treatment for the antipsychotic-induced movement disorder.

Warnings

• Because of the relatively high incidence of depression, it has been recommended that people with a history of depression avoid taking tetrabenazine. Research into this is ongoing however, and this warning may be dropped in the future.
• The concomitant intake of MAO inhibitors is contraindicated.

References

1. ^ Guangrong Zheng et al. (2006): "Vesicular Monoamine Transporter 2: Role as a Novel Target for Drug Development", AAPSJ. Fulltext
2. ^ Jankovic J, Beach J (1997). "Long-term effects of tetrabenazine in hyperkinetic movement disorders.". Neurology 48 (2): 358-62. PMID 9040721.