Xenanine (Tetrabenazine) was approved by the FDA earlier this month, but it will take several more months for the drug to be available in pharmacies. During this time Prestwick Pharmaceuticals, the sponsoring drug company will begin manufacturing and distributing it, and they will need to put significant effort into educating doctors and pharmacists in its proper use. Don't be afraid to use this drug if your chorea warrants it, but make sure you educate yourself about the side effects too . .
Tetrabenazine (TBZ) helps control chorea by decreasing dopamine
levels in the brain. Proper dosage of this drug is very important.
My advice to you and your doctor is to start low (6.25 to 12.5
mg/day) and go slow, increasing dosage in one or two week
intervals. It is important to see your doctor frequently to
establish best dosing; one that controls some of the chorea without
causing side effects. The goal is not to stop the chorea completely
because the dosages required could lead to serious side effects.
Common side effects are fatigue and sleepiness, depression,
Parkinsonism (slowness of movement), restlessness. Often decreasing
the dosage will control side effects.
Depression is the most serious side effect and occurs because this drug also decreases levels of serotonin and norepinephrine in the brain, both of which are needed for maintaining good mood. It is important for your family and doctor to check for depression even after a stable dosage is found. If depression occurs, the tetrabenazine dosage should be decreased or an antidepressant added. At present, there are no official recommendations regarding use of antidepressants with tetrabenazine. Previous depression is not a contraindication for use of this drug, but there is increased chance of worsening depression [Kenney C 2006].
It is best to avoid paroxetine (Paxil®) and the tricyclic antidepressants like amytriptyline (Elavil®) and nortriptyline (Pamalor®) because these drugs can increase the blood levels of TBZ. It is probably best to use a different antidepressant or to decrease Paxil® dosage if used with Tetrabenazine. Tetrabenazine can also increase the side effects of antipsychotic drugs.
At least in my own experience, tetrabenazine dosage can be decreased over time while maintaining affect. Unless medically indicated this drug should not be stopped quickly, but in tapering doses.
Editor's Comments: Used carefully this drug has improved the quality of life greatly for many with Huntington's. My patients treated with tetrabenazine have had increased comfort and desire for socialization. One who wouldn't leave home now gets out several times a week. They report better balance and fewer falls. They describe improved ability to talk and read, improved mechanics of eating, a return to gardening, even riding a bike again.
There certainly are benefits for many; but as with any medication, use it carefully and don't forget to see your doctor.
Kenney C, Hunter C, Mejia N, Jankovic J. Is history of depression a contraindication to treatment with tetrabenazine?. Clin Neuropharmacol. 2006 Sep-Oct;29(5):259-64. PubMed abstract