Chorea is a movement disorder characterized by involuntary muscle contractions. It is thought to be caused by problems with the regulation of chemical signals released by nerve cells, which control muscle movement. For information sent from the brain to reach a muscle, it has to be passed through a long line of nerve cells. This requires each cell in the line to release chemical messengers. For the information to be passed from one nerve cell to another, sacs known as vesicles must gather up and transport the chemical signal, which they release near an adjacent nerve cell.
The involuntary muscle movement seen in Huntington’s disease involves the excessive release of one such chemical called dopamine.
How Austedo works
Austedo works in the same way as another FDA-approved therapy called Xenazine (tetrabenazine). Both inhibit the vesicles that carry dopamine to the area between two nerve cells where it is released. This kind of vesicle is known as a vesicular monoamine transporter 2 (VMAT2).
Both Austedo and Xenazine bind to VMAT2, reducing the amount of dopamine released from nerve cells and dialing back the stimulation of adjacent nerve cells. This prevents the overstimulation of muscles that causes chorea.
Austedo has a longer half-life, meaning it is degraded slower, than Xenazine, whose short half-life in the body means its effects wear off within hours of a patient taking it. By altering Austedo’s chemical structure, scientists were able to prolong its effects.
Austedo in clinical trials
Austedo’s ability to reduce chorea in Huntington’s disease patients was assessed in a randomized, double-blind, placebo-controlled Phase 3 clinical trial (NCT01795859).
Researchers included 90 Huntington’s disease patients with chorea, and assessed their total maximal chorea (TMC) scores nine and 12 weeks after beginning treatment.
The TMC scores of patients receiving Austedo improved. But a week after they stopped taking the medication, their scores reverted back to their initial values.
VMAT2 inhibitors such as Austedo can not only worsen mood but also reduce a person’s ability to function and think. Austedo can also increase the risk of depression, as well as suicidal thoughts and behavior.
Austedo is not recommended for anyone with a liver condition or anyone taking other treatments for depression called monoamine oxidase inhibitors.
The most common adverse reactions recorded during the clinical trial were sleepiness, diarrhea, dry mouth, and fatigue.
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