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Phase 3 Study of Pridopidine Hydrochloride for Safety and Efficacy in Adults with Huntington’s Disease

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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study focuses on Huntington’s disease, a rare inherited brain disorder that causes movement problems, thinking difficulties, and mood changes. Participants will receive an oral capsule containing 90 mg of Pridopidine, or a matching placebo that looks the same but contains no active medicine.

The aim is to see whether the drug can slow the clinical progression of the condition. In this phase 3 trial, volunteers are randomly assigned to one of the two groups and neither the participants nor the study staff know which treatment is given. The study lasts about one year, with regular visits to check health, record any side effects, and collect information about daily functioning.

Effectiveness will be judged by changes from the start of the study to week 52 in several areas: the overall disease rating measured by the cUHDRS score, the ability to perform everyday tasks assessed with the Total Functional Capacity score, fine motor skill evaluated through a finger‑tapping test called Quantitative Motor, and thinking speed measured by a reading test known as Stroop Word Reading. Safety will be monitored by recording any treatment-emergent adverse events that appear during the trial.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment and Randomization

    You agree to join the study and sign the consent form. The study staff assigns you randomly to receive either the active drug or a matching placebo. Neither you nor the study staff will know which one you receive.

  2. Step 2

    Baseline Assessments

    At the first visit, the research team records your current health status, measures your Huntington’s disease symptoms using standard scales, and collects laboratory samples. These measurements serve as the baseline for later comparison.

  3. Step 3

    Start of Study Medication

    You begin taking one hard capsule by mouth each day. If you are assigned to the active group, the capsule contains 90 mg of pridopidine hydrochloride. If you are assigned to the control group, the capsule contains no active drug (placebo). You continue this daily dose for the next 52 weeks.

  4. Step 4

    Ongoing Daily Dosing

    You keep taking the study capsule every day at roughly the same time. You should not change the dose unless instructed by the study doctor. You may be asked to keep a simple diary noting each dose.

  5. Step 5

    Safety Monitoring Visits

    Throughout the year, you attend scheduled clinic visits. During these visits the staff checks for any side effects, records any new health problems, and may perform blood tests. This monitoring helps ensure your safety while you are on the study medication.

  6. Step 6

    Week 52 Evaluation

    At the end of week 52, the team repeats the same assessments that were done at baseline. They measure the change in the composite Unified Huntington's Disease Rating Scale (cUHDRS), functional capacity using the Total Functional Capacity score, motor function with the Quantitative Motor Finger Tapping Inter‑onset Interval, and cognition with the Stroop Word Reading test. They also document any treatment‑emergent adverse events and serious adverse events that occurred during the study.

  7. Step 7

    Study Completion

    After the final assessments, you stop taking the study capsule. The study data are collected and analyzed. You will continue to receive standard medical care for Huntington’s disease as advised by your regular physician.

Who can join the trial?

9 criteria

  • Be an adult between 23 and 65 years old at the time of screening.
  • Have Huntington’s disease that first showed signs at age 21 or older.
  • Have a confirmed diagnosis based on symptoms and a test showing ≥40 CAG repeats in the HTT (huntingtin) gene. (CAG repeats are a specific DNA pattern that is longer in people with the disease.)
  • Show clear movement (motor) signs with a diagnostic confidence level of 4, meaning the doctor is at least 99% sure of the diagnosis.
  • Score at least 7 on the Total Functional Capacity (TFC) assessment, which measures ability to perform everyday activities.
  • Have a CAG‑Age Product (CAP)100 score of 95 or higher. (This score combines the number of CAG repeats and the person’s age to estimate disease progression.)
  • Score 90% or less on the Independence Scale (IS), which rates how independent a person is in daily life.
  • Score 20 or higher on the Total Motor Score (TMS), which measures the severity of movement problems.
  • Not have taken certain medicines called ADMs (including VMAT2 inhibitors and neuroleptic/antipsychotic drugs) for at least six months before the screening visit.

Who cannot join the trial?

12 criteria

  • Having serious heart problems, such as a prolonged QT interval (a heart‑rhythm measurement) over 450 ms for men or 470 ms for women, irregular heartbeats (arrhythmias), uncontrolled atrial fibrillation (a type of irregular heartbeat), or a birth‑related long QT condition.
  • Having a history of seizures within the past five years.
  • Having major brain or nerve problems, like damage inside the skull (intracranial pathology) or strokes (cerebrovascular events).
  • Having an active or recent cancer (unless it was a small, localized tumor that has been fully treated).
  • Having any serious or uncontrolled body‑wide disease, such as severe liver disease (hepatic), severe kidney disease (renal), serious lung, hormone, infection (including hepatitis B, hepatitis C, or HIV), or psychiatric illnesses that could affect safety or study participation.
  • Having severe liver or kidney problems that significantly reduce their function.
  • Having taken any therapy that lowers the mutant huntingtin protein (mHTT‑lowering therapy) in the past year.
  • Taking medicines that can lengthen the QT interval within four weeks before the first study visit.
  • Having used the study drug pridopidine within six weeks (or five drug half‑lives) before the screening visit.
  • Having previously taken part in a study that used gene therapy delivered directly into the brain (intracranial gene therapy).
  • Having lab test results that are far outside the normal range and are judged by the doctor to be unsafe or make the person unsuitable for the study.
  • Being a woman who is pregnant, planning to become pregnant, or currently breastfeeding.
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Investigated drugs

Pridopidine is an oral medication being studied as a possible treatment for Huntington’s disease. It comes in a hard capsule that participants swallow. In this Phase 3 trial, the drug is given to see if it can slow the clinical progression of the disease and improve safety and overall health for people with Huntington’s disease. The study will closely monitor how well the medication works and any side effects that may occur.

What is already known about the treatment

PRIDOPIDINE - Pridopidine is taken as a hard capsule by mouth, typically 90 mg once daily. It is still an investigational drug with orphan‑drug status and is being studied mainly in clinical trials for Huntington’s disease. The medicine aims to slow the progression of Huntington’s disease symptoms, especially motor and functional decline. It works by activating the sigma‑1 receptor in brain cells, which helps protect neurons and improve their communication, classifying it as a sigma‑1 receptor agonist and neuroprotective agent.

Investigated diseases

Huntington’s disease - Huntington’s disease is a genetic disorder that causes the brain’s nerve cells to slowly break down over time. It typically begins in a person’s 30s or 40s and leads to involuntary movements, problems with coordination, and difficulty thinking clearly. As the disease progresses, people may experience increasing challenges with daily activities, memory, and mood. The condition worsens gradually, with symptoms becoming more severe over many years.
Trial detailsLast updated 14 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2026-526093-16-00Protocol codePL101-HD302Estimated enrolment272 patientsSponsorFerrer Internacional S.A.

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