Safety and Efficacy of Deutetrabenazine at High versus Lower Daily Dosages in the ARC-HD Study to Treat Chorea in Huntington Disease.

Background: Huntington disease (HD) is a progressive neurodegenerative disease that causes psychiatric and neurological symptoms, including involuntary and irregular muscle movements (chorea). Chorea can disrupt activities of daily living, pose safety issues, and may lead to social withdrawal. The vesicular monoamine transporter 2 inhibitors tetrabenazine, deutetrabenazine, and valbenazine are approved treatments that can reduce chorea.

Objective: This post hoc analysis was conducted to evaluate safety and efficacy among participants who received high-dosage deutetrabenazine treatment (> 48 mg/d) in ARC-HD, an open-label study that assessed long-term safety and efficacy of deutetrabenazine for the treatment of chorea in HD in adults.

Methods: ARC-HD was a single-arm, two-cohort, open-label study. Participants either successfully completed the First-HD study or switched overnight from tetrabenazine to deutetrabenazine. Participants were dosed with deutetrabenazine in a response-driven manner (maximum 72 mg/d allowed). For the current analysis, exposure-adjusted incidence rates (EAIRs) for adverse events of interest were analyzed according to daily dosage (≤ 48 mg/d versus > 48 mg/d), and total maximal chorea (TMC) scores were analyzed by cohort during the stable-dose period.

Results: In total, 116 of the 119 participants enrolled in ARC-HD entered the stable-dose period, where no apparent differences were seen in EAIRs when receiving deutetrabenazine dosages ≤ 48 mg/d (exposure = 177.7 person-years) compared with > 48 mg/d (exposure = 74.1 person-years). Similar results were found among the subset of participants who received deutetrabenazine dosages > 48 mg/d at least once during the study (n = 49, 42%) when their dosage was ≤ 48 mg/d (exposure = 37.9 person-years) versus > 48 mg/d (74.1 person-years). Efficacy analyses were conducted for participants who had TMC scores available (rollover cohort, n = 77; switch cohort, n = 35). For most participants, the lowest deutetrabenazine dosage needed to achieve a TMC response (≥ 30% improvement from baseline) was between 24 and 48 mg/d in both the rollover (n = 57, 74.0%) and switch (n = 16, 46.0%) cohorts. Whereas the dosage needed for a TMC response was independent of baseline TMC score in the rollover cohort, participants with higher baseline TMC scores in the switch cohort required higher dosages to achieve a TMC response during the trial.

Conclusions: In this open-label, long-term study, some participants received deutetrabenazine dosing > 48 mg/d to achieve adequate chorea control. There was no new safety concern or incremental change in the safety profile between dosages of ≤ 48 mg/d and > 48 mg/d. These results include dosages that have not been approved for clinical use, however, they increase our understanding of safety and tolerability of deutetrabenazine doses.

Clinical trials registration: ARC-HD (ClinicalTrials.gov identifier: NCT01897896); First-HD (ClinicalTrials.gov identifier: NCT01795859).