Despite improvements in the tolerability of antipsychotic medications, the development of tardive dyskinesia (TD) still is a significant area of concern; however, clinicians have had few treatment options. Valbenazine, a vesicular monoamine transport type 2 (VMAT2) inhibitor, is the only FDA-approved medication for TD (Table 1).1 By modulating dopamine transport into presynaptic vesicles, synaptic dopamine release is decreased, thereby reducing the postsynaptic stimulation of D2 receptors and the severity of dyskinetic movements.
In the pivotal 6-week clinical trial, valbenazine significantly reduced TD severity as measured by Abnormal Involuntary Movement Scale (AIMS) ratings.2 Study completion rates were high (87.6%), with only 2 dropouts because of adverse events in each of the placebo (n = 78) and 40-mg (n = 76) arms, and 3 in the 80-mg group (n = 80).
Before the development of valbenazine, tetrabenazine was the only effective option for treating TD. Despite tetrabenazine’s known efficacy for TD, it was not available in the United States until 2008 with the sole indication for movements related to Huntington’s disease. U.S. patients often were subjected to a litany of ineffective medications for TD, often at great expense. Moreover, tetrabenazine involved multiple daily dosing, required cytochrome P450 (CYP) 2D6 genotyping for doses >50 mg/d, had significant tolerability issues, and a monthly cost of $8,000 to $10,000. The availability of an agent that is effective for TD and does not have tetrabenazine’s kinetic limitations, adverse effect profile, or CYP2D6 monitoring requirements represents an enormous advance in the treatment of TD.
Tardive dyskinesia remains a significant public health concern because of the increasing use of antipsychotics for disorders beyond the core indication for schizophrenia. Although exposure to dopamine D2 antagonism could result in postsynaptic receptor upregulation and supersensitivity, this process best explains what underlies withdrawal dyskinesia.3 The persistence of TD symptoms in 66% to 80% of patients after discontinuing offending agents has led to hypotheses that the underlying pathophysiology of TD might best be conceptualized as a problem with neuroplasticity. As with many disorders, environmental contributions (eg, oxidative stress) and genetic predisposition might play a role beyond that related to exposure to D2 antagonism.3
There have been trials of numerous agents, but no medication has been FDA-approved for treating TD, and limited data support the efficacy of a few existing medications (clonazepam, amantadine, and ginkgo biloba extract [EGb-761]),4 albeit with small effect sizes. A medical food, consisting of branched-chain amino acids, received FDA approval for the dietary management of TD in males, but is no longer commercially available except from compounding pharmacies.5