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A study comparing prasinezumab with placebo for people with early-stage Parkinson's disease

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What is this trial about?

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

This study is looking at Early-Stage Parkinson's Disease, which is a condition that affects movement and can cause symptoms such as slowness of movement, trembling at rest, and muscle stiffness. The study will test a treatment called prasinezumab, which is also known by the code name RO7046015. This medication is a type of antibody that is designed to target a specific protein involved in Parkinson's Disease. Some participants will receive prasinezumab while others will receive placebo. The purpose of the study is to compare how well prasinezumab works compared with placebo in slowing down the worsening of movement problems in people with early-stage Parkinson's Disease.

Participants in this study will have been diagnosed with Parkinson's Disease and will already be taking medication for their condition for at least three months. The study will look at whether prasinezumab can delay the time it takes for movement problems to get worse. Prasinezumab will be given through an intravenous infusion, which means it will be delivered directly into a vein. The study will measure various aspects of how participants move and function, including detailed assessments of motor function, which refers to how well a person can control their body movements.

During the study, doctors will carefully monitor participants for any side effects or unwanted reactions to the treatment. This includes checking for infusion-related reactions, which are responses that can happen when medication is given through a vein. Regular health checks will be performed, including measurements of vital signs such as blood pressure and heart rate, blood tests, and assessments of overall wellbeing. The study will also track changes in the amount of Parkinson's Disease medication that participants need to take over time, as well as how participants feel about changes in their condition.

The research process

The trial runs in 8 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial assessment and confirmation

    Your diagnosis of Parkinson's disease will be confirmed based on specific criteria established by the Movement Disorder Society. This means your condition must include bradykinesia (slowness of movement) plus at least one other main sign such as resting tremor (shaking when muscles are relaxed) or rigidity (stiffness).

    Your current stage of Parkinson's disease will be assessed using the Hoehn and Yahr scale, which measures disease progression. You must be at Stage 1 or 2 when not taking medication, indicating early-stage disease.

    Your score on the MDS-UPDRS Part IV assessment, which evaluates motor complications, must be 0. This means you should not have motor complications from your current treatment.

    You must have been taking Parkinson's disease medication for at least 3 months before starting the study.

  2. Step 2

    Randomization and treatment assignment

    You will be randomly assigned to receive either prasinezumab or placebo. The placebo is an inactive substance that looks identical to the actual medication but contains no active ingredient.

    Neither you nor your medical team will know which treatment you are receiving. This is called a double-blind study design and helps ensure accurate results.

  3. Step 3

    Treatment administration

    You will receive your assigned treatment through an intravenous infusion, which means the medication will be delivered directly into your vein through a needle.

    The infusion will be given at regular intervals throughout the study period.

  4. Step 4

    Regular monitoring and assessments

    Your motor function will be regularly assessed using the MDS-UPDRS Part III scale. This evaluation measures movement-related symptoms when you are not taking your regular Parkinson's medication.

    The medical team will monitor for any motor progression events, which means a confirmed worsening of your movement symptoms.

    Your vital signs, including blood pressure, heart rate, and temperature, will be measured at each visit.

    Blood samples will be taken at specific times to check various laboratory parameters, including hematology (blood cell counts), clinical chemistry (chemical components in blood), coagulation (blood clotting ability), and urinalysis (urine tests).

    An electrocardiogram (ECG) will be performed to monitor your heart's electrical activity.

    You will be assessed for any suicidal thoughts or behaviors using the Columbia Suicide Severity Rating Scale.

    The medical team will monitor for any side effects or adverse reactions, including infusion-related reactions that may occur during or after the treatment administration.

  5. Step 5

    Week 104 assessment

    At Week 104 (approximately 2 years after starting), a comprehensive assessment of your motor function will be conducted using the MDS-UPDRS Part III score while you are off your regular medication.

    Changes in your motor function from the beginning of the study will be evaluated.

  6. Step 6

    Ongoing evaluations throughout the study

    Your self-reported motor function will be assessed to determine if there is any worsening.

    The Clinical Global Impression of Change (CGI-C) Overall Disease Subscale will be used to evaluate meaningful changes in your overall condition.

    Any increases in your LEDD (levodopa equivalent daily dose), which measures the total amount of Parkinson's medication you take, will be monitored.

    Blood samples will be collected at specified times to measure the concentration of prasinezumab in your blood and to check for anti-drug antibodies, which are proteins your immune system might produce in response to the medication.

  7. Step 7

    Contraception requirements

    You must follow specific contraception requirements throughout the study period as agreed upon at the start.

  8. Step 8

    Study completion

    The study is expected to continue until July 2031, though your individual participation duration may vary.

    Throughout the entire study period, any adverse events will be classified according to the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) version 5.0, which provides a standardized way to describe the severity of side effects.

Who can join the trial?

5 criteria

  • You must have a diagnosis of idiopathic Parkinson's Disease, which means Parkinson's Disease that occurs on its own without a known cause, confirmed by specific medical criteria. Your diagnosis must include bradykinesia (slowness of movement) plus at least one other main sign such as resting tremor (shaking when your muscles are relaxed) or rigidity (muscle stiffness).
  • You must have been taking medication for Parkinson's Disease for at least 3 months before starting the study.
  • You must have a score of 0 on a specific rating scale called MDS-UPDRS Part IV at the screening visit and before being assigned to a treatment group. This scale measures complications related to Parkinson's Disease treatment.
  • You must be at Hoehn and Yahr Stage 1 or 2 when not taking your medication during the screening visit and before being assigned to a treatment group. This staging system describes how severe your Parkinson's Disease symptoms are, with Stage 1 and 2 being early stages of the disease.
  • You must agree to follow the required contraception (birth control) methods during the study.

Who cannot join the trial?

14 criteria

  • You have a type of parkinsonism (a movement disorder similar to Parkinson's disease) that is caused by medications, genetic conditions, or other brain diseases
  • You have had brain surgery for Parkinson's disease, such as deep brain stimulation (a treatment where electrodes are placed in the brain to help control symptoms)
  • You have significant memory problems or dementia (a condition that affects memory and thinking abilities)
  • You have a history of psychosis (a mental condition where you see or hear things that are not real or have unusual beliefs)
  • You have other serious brain or nerve conditions besides Parkinson's disease
  • You have uncontrolled high blood pressure or heart disease
  • You have serious liver or kidney problems
  • You have active cancer or have been treated for cancer in the recent past
  • You have a history of serious infections or immune system problems
  • You are pregnant, breastfeeding, or planning to become pregnant during the study
  • You have had a serious allergic reaction to medications similar to the study drug
  • You are taking certain medications that could interfere with the study treatment
  • You have participated in another clinical trial recently
  • You have any other medical condition that the doctor believes would make it unsafe for you to participate
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Investigated drugs

  • Prasinezumab

    is an experimental medication given through an intravenous infusion (directly into a vein). It is being tested to see if it can help slow down the progression of early-stage Parkinson's disease. This medication is designed to target a specific protein that may be involved in the disease process.

  • Placebo

    is an inactive substance that looks like the real medication but contains no active treatment. It is used in this study to compare against prasinezumab to help determine if the actual medication is working.

What is already known about the treatment

Prasinezumab – Prasinezumab is an experimental medication given through an intravenous infusion (directly into a vein) that is currently being studied in Phase III clinical trials for the treatment of early-stage Parkinson's disease. This medication works by targeting and binding to a protein called alpha-synuclein, which abnormally accumulates in the brain cells of people with Parkinson's disease, potentially slowing down the progression of the condition. The drug belongs to a class of medications known as monoclonal antibodies, which are designed to recognize and attach to specific proteins in the body. At this time, prasinezumab is still under investigation and has not yet been approved for general medical use, as researchers are evaluating whether it can effectively slow the worsening of Parkinson's symptoms compared to placebo.

Investigated diseases

Early-Stage Parkinson's Disease – Parkinson's disease is a brain disorder that affects movement and gets worse over time. In the early stage, symptoms are mild and may include slight tremors, small changes in handwriting, or reduced arm swing when walking. The disease develops when certain nerve cells in the brain that produce dopamine, a chemical messenger important for controlling movement, gradually break down or die. As the condition progresses, movements become slower and more difficult, and muscles may become stiff. People may also notice balance problems and changes in their posture. The early stage is the period when symptoms are present but have not yet significantly impacted daily activities.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-522683-32-00Protocol codeBN44715Estimated enrolment1 010 patientsSponsorF. Hoffmann-La Roche AG

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