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Study of apomorphine and rifaximin for Parkinson's disease patients with reduced levodopa effectiveness

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What is this trial about?

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

This clinical trial focuses on Parkinson's disease, a progressive nervous system disorder that affects movement. The study aims to improve symptom management in patients whose bodies break down levodopa (a standard medication for Parkinson's disease) too quickly. The research will test different treatment approaches using several medications: apomorphine (a medication that directly stimulates dopamine receptors in the brain), rifaximin (an antibiotic), and a placebo.

The study will compare how well these different treatments work in patients who have difficulty with their regular Parkinson's medication. Participants will receive either Dacepton (which contains apomorphine) as an injection under the skin, Xifaxan (which contains rifaximin) as tablets taken by mouth, or placebo capsules. Some participants will also continue taking their regular Madopar medication, which contains a combination of levodopa and benserazide.

During the study, patients will take different combinations of these medications. Domperidone tablets may be given to some participants to prevent possible side effects. The treatment period will last for several weeks, during which the effectiveness of these different approaches will be evaluated to determine which method works best for managing Parkinson's disease symptoms in patients who have this specific problem with levodopa treatment.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

Step 1
Initial treatment phase
You will receive levodopa (Madopar 125 mg) in combination with domperidone (10 mg tablets) for symptom management
The medication will be taken by mouth according to your prescribed schedule
Your response to the treatment will be measured using specific movement assessments
Step 2
Treatment with rifaximin or placebo
You will be given either rifaximin (Xifaxan 550 mg film-coated tablets) or placebo capsules
The tablets are to be taken by mouth
Neither you nor your doctor will know whether you are receiving the active medication or placebo
Step 3
Apomorphine treatment phase
You will receive apomorphine (Dacepton 10 mg/ml) through subcutaneous injection
This medication is delivered under the skin using a special cartridge system
Your movement symptoms will be assessed to measure the treatment response
Step 4
Monitoring and assessment
Your condition will be evaluated using several rating scales that measure movement ability
You will need to temporarily stop taking your regular Parkinson's medication for up to 12 hours on multiple occasions
Biological samples will be collected throughout the study
The total duration of the study is from December 2024 to February 2026

Who can join the trial?

8 criteria

Must be at least 25 years old
Can be either male or female
Must be able to read and understand Dutch language
Must sign an informed consent form that has been approved by the ethics board
Must be willing and able to: - Follow all study requirements - Stop taking Parkinson's medication for up to 12 hours at multiple times - Provide biological samples when required
Must have Parkinson's disease diagnosed by a neurologist according to standard clinical criteria
Must have documented levodopa resistance (reduced response to standard Parkinson's medication)
Must have either: - Increased levels of AADC enzyme (a protein that breaks down levodopa) in blood, or - Increased levels of TDC enzyme (another protein that breaks down levodopa) in stool samples

Who cannot join the trial?

15 criteria

Current use of antibiotics or having taken them within the last 30 days
Known allergic reactions to apomorphine or rifaximin
History of severe heart disease or recent heart attack (within last 6 months)
Severe liver problems or abnormal liver function tests
Severe kidney disease requiring dialysis
Presence of dementia (significant memory and thinking problems)
History of alcohol or drug abuse within the past year
Pregnant women or women planning pregnancy
Breastfeeding mothers
Current participation in other clinical trials
Having deep brain stimulation (a surgical treatment where electrodes are placed in the brain)
Severe depression or other major psychiatric disorders
Unable to follow study instructions or attend regular visits
History of frequent fainting episodes
Severe digestive system disorders

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Stichting Radboud University Medical Center
Nijmegen, The Netherlands

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Investigated drugs

Levodopa
is a medication that helps manage Parkinson's disease symptoms by converting into dopamine in the brain. It is the most common treatment for Parkinson's disease, helping to control tremors, stiffness, and movement difficulties.
Apomorphine
is a medication that directly stimulates dopamine receptors in the brain, bypassing the need for conversion by enzymes. It can be helpful for Parkinson's disease patients who don't respond well to levodopa treatment.
Rifaximin
is an antibiotic medication that works in the digestive system. In this trial, it is being studied for its potential to reduce bacteria that may interfere with Parkinson's disease medications by producing certain enzymes.

What is already known about the treatment

Levodopa
An oral medication that serves as the primary treatment for Parkinson's disease by converting into dopamine in the brain to help control movement symptoms. It crosses the blood-brain barrier and works by replenishing depleted dopamine levels in the brain's motor control regions, making it the most effective medication for managing Parkinson's symptoms. The medication is typically taken several times daily in tablet form, often in combination with carbidopa to prevent its breakdown before reaching the brain.
Apomorphine
A injectable dopamine receptor agonist used in advanced Parkinson's disease when oral medications become less effective. It works by directly stimulating dopamine receptors in the brain, bypassing the need for conversion like levodopa, and provides rapid relief from "off" episodes when movement becomes difficult. The medication is administered via subcutaneous injection or continuous infusion pump, making it particularly useful for patients who have developed resistance to oral medications.
Rifaximin
An oral antibiotic that works primarily in the intestinal tract without significant absorption into the bloodstream. In Parkinson's disease research, it is being studied for its potential role in modifying gut bacteria that may affect levodopa metabolism. The medication is taken in tablet form and belongs to the rifamycin class of antibiotics, traditionally used for treating gastrointestinal infections but now being investigated for its potential therapeutic effects in neurological conditions.

Investigated diseases

Parkinson's disease - A progressive neurological disorder that affects movement and motor control. The condition develops when nerve cells in a specific part of the brain begin to break down and die, leading to decreased production of dopamine, a crucial chemical messenger. The disease typically causes tremors, particularly in the hands, arms, legs, and face, as well as stiffness or slowing of movement. People with Parkinson's disease may also experience changes in their balance, coordination, and speech patterns. The symptoms usually start gradually and worsen over time, with one side of the body often being affected first before spreading to both sides.