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Parkinson's clinical trials

Clinical trials

There is currently no cure for Parkinson’s so research into new and improved treatments is vital. There are therefore many Parkinson's clinical trials (also known as clinical studies) that aim to find new and improved ways to treat, manage, prevent, diagnose and cure the condition.

Clinical trials are medical research studies carried out in humans. Such trials are the best way to find out whether a new treatment:

  • is safe
  • is beneficial to people with Parkinson’s
  • is more effective than current treatments for some people
  • can improve the quality of life for people with Parkinson’s.

Clinical trials follow a strict protocol or process, meaning that new treatments are tested in a controlled way to minimise any risk to participants. Their effect is carefully monitored and in addition to determining their effectiveness, data is collected on safety aspects such as adverse reactions, absorption and excretion of the new drug and interaction with other medications. Sometimes a trial will study the effects of using an existing treatment in different ways.

Clinical research is an expensive process which requires considerable financial support. This comes from a range of sponsors including the pharmaceutical industry, governments, and academic and research organisations.

How might clinical trials help in Parkinson’s?

Clinical trials can help people with Parkinson’s in many ways. Some of the benefits include:

  • broadening our understanding of Parkinson’s so that treatments can become more effective
  • giving people with Parkinson’s the opportunity to be involved in research which uses the most up-to-date treatments and devices
  • helping to improve quality of life for people with Parkinson’s
  • improving treatment for future generations of people with Parkinson’s
  • leading us closer to a cure.

The trial process

All medications must undergo rigorous testing before they can be approved for use. The trial process is lengthy, complex and carries significant costs to the pharmaceutical industry. Only a small minority of treatments reach the final stages of a trial and receive approval to be marketed.

The various stages of trials have a specific purpose as outlined below.

1. Developing and testing a compound in a laboratory

When researchers suspect that a product or compound may be beneficial, they will first check to see if any relevant research papers have been published and will carefully study any findings.

Researchers will consider how a potential new drug may work in the brain and will screen large numbers of chemical compounds, shortlisting a small number for pre-clinical studies.

Initial research may take place in a laboratory as scientists develop a compound that they think may help with a particular condition or symptom. Occasionally new treatments are discovered by accident or are found to have a use that was unexpected.

2. Pre-clinical animal testing

Initial tests, referred to as “pre-clinical studies” are carried out in animals - often mice, rats and occasionally monkeys - to see if the treatment works as predicted. Such tests will also monitor any adverse effects to other organs and if the treatment causes illness or malformation. In the past, Parkinson’s has been induced in animals by injecting a compound known as MPTP (1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine), a neurotoxin which causes the dopamine producing cells in the brain to die just as they do in human Parkinson’s. This is used as a model to test whether a drug can help to overcome some of the movement problems associated with Parkinson’s. However, more recent models involve the genetic modification of animals to allow us to assess whether a new drug may actually influence the rate at which the condition progresses, that is, they are "disease-modifying” drugs.

If pre-clinical tests appear to be safe and have the desired effect then the treatment company must apply to the appropriate national or international body for permission to begin human trials. This can be done at a national level, such as to the Medicines & Healthcare Products Regulatory Agency (MHRA) in the UK, or as a pan-European application to the European Medicines Agency (EMA). In the USA, the regulatory authority is the Food and Drugs administration (FDA). This formal application will include a study plan or protocol. This will detail information regarding studies that have been carried out to date, why it is believed that the treatment being assessed might be effective for a particular condition, the anticipated risks and benefits for volunteers, the eligibility criteria for participating in the study, the process by which volunteers are enrolled (known as informed consent), and how long the trial should last. It is important that there is significant patient input into the the trial design, particularly to determine how the effectiveness of the drug will be measured.

3. Clinical trials (testing in humans)

Once it has been established that the compound is safe in animals and permission is granted, testing on humans can begin. Clinical testing is usually broken down into four different phases.

  • Phase I - this phase is usually carried out in a small number of healthy individuals (10-80) who do not have the condition for which the treatment is being tested. The medicine is used in low doses initially to test safety and side effects, always under careful monitoring and often in a hospital setting. If initial results are positive, the dosage may be increased gradually so that researchers can ascertain what a safe and well-tolerated dose might be. For advanced therapies which are particularly invasive, such stem cell or gene therapies, phase I is usually carried out in people with the condition it aims to treat.
  • Phase II – the treatment is used on a larger group of people (100-300) with the condition it is intended to treat. This is critical for deciding whether or not a treatment is effective enough for it to continue into a larger trial. Based on the results of the phase I study, the optimal doses will be used and specific side effects will be monitored in detail. It is important at this stage to define what is meant by the drug being “effective”. Only about a third of treatments trialled successfully complete phases I and II. 

    Phase II trials are usually ‘double-blind’, which means a number of people (sometimes known as the experimental group) are randomly chosen to follow a course of the active treatment. Another group (known as the control group) are given a recognised, standard therapy or, less commonly in Parkinson’s, a placebo. It is double-blind because none of those involved – neither those who are taking part in the trial, nor doctors and researchers – know who is taking the new treatment and who is in the control group. This means that their findings cannot be prejudiced in any way. 
  • Phase III – if phase II results are positive then the study is extended to a much larger group (1,000-3,000) in the hope that this will reinforce findings and show that initial success in the previous phase was not random. The results of this phase provide more detailed information on how effective the treatment is, how it compares to treatments already available, and the benefits, risks and optimal dosages.

    Phase III trials are also ‘double-blind’.

    At the end of the agreed testing period - which can last from several weeks to several years – the trial is  ‘unblinded’ and it is revealed who has been taking the new treatment and who has been following the ‘control’ treatment. Conclusions can then be drawn from the results of this stage of testing. The desirable result is of course that those on the treatment under trial have shown more improvement than the other group of volunteers.

    Some trials are also ‘open label’ which means that the participants and researchers know what treatment is being taken and there is no ‘blind’ element to the study. However, these are not common for Parkinson’s as the “placebo effect” is particularly strong. Essentially, when a person thinks that they are receiving a drug, they will show some positive effects, even though there may be no active drug in the tablet that they take. This can last up to six months, so it is important that this is taken into account when designing a Parkinson’s study.

    Whatever the format of the trial, volunteers are very closely monitored at all times and tests are carried out, including blood and heart tests. If any safety concerns arise, the trial may be stopped. 

    It is estimated that about 70-90% of phase III trials have a successful outcome although the drugs may not ultimately be available for treatment as they may not be sufficiently more effective than existing therapies.

  • Phase IV - assuming that all previous phases are successfully completed, the treatment company will apply to the regulatory authorities for permission to use as an approved treatment. This process is very detailed and time consuming and can take one to two years to complete. During the approval process, further data will be collected and additional information may be requested by the regulators. However, until the treatment has been registered it cannot be made more widely available. And even once registered and widely used, a new treatment is still monitored for safety. Patients can report adverse or side effects on the European Medicines Agency (EMA) website. There may also be similar facilities available at a national level.

Getting involved in Parkinson's clinical trials

There is often a shortage of volunteers for trials. This may be due to a lack of easily available information on trials in a particular location or area, or to doctors being unaware of trials that are being held locally.

If you would like to become involved in a trial it is essential to discuss this first with your doctor. Find out as much information as possible about the trial so that you can fully discuss your participation. Your doctor will be able to advise on the advantages and disadvantages in your own particular situation, and they may be able to refer you to other members of the multidisciplinary team who have more knowledge about a particular area of research.

Depending on what the trial is investigating, the research team will be looking for people who fit specific criteria – called inclusion and exclusion criteria (or eligibility criteria) – that ensure you are suitable for the trial. Screening usually involves answering questions about your Parkinson’s, your medication, treatment history and checking details such as your age and when you were diagnosed. You may need to have blood tests, scans or other tests as well. If you fit the team’s criteria you can then be invited to take part in the trial.

What are the benefits and risks in participating?

There are many benefits to taking part in a trial. You may feel that by doing so you are playing a more active role in your health as well as helping scientists to find new medications to help others or move closer to a cure. You may be able to access research treatments before they become widely available. Participation can also provide opportunities to learn more about Parkinson’s and to meet others in a similar situation. 

The safety of participants is always paramount and there are strict codes of practice that must be observed to protect volunteers. Individual names of participants are not disclosed.

However, as with any new treatment, there will always be an element of risk involved, although every care will be taken to eliminate the risk of serious or even life-threatening side effects. The phase I trial of the study is always designed to strictly assess the safety of the medicine and it will be terminated if any significant adverse effects are reported.

No assurance can be given when entering a trial that the treatment will improve your condition and, in some cases, this may deteriorate in the absence of effective medication. It is likely, though, that you would be taken off the trial if your condition were to worsen; this is something you should discuss with your doctor. You may also experience unwanted side effects or need to undergo tests such as blood tests or scans which you may find unpleasant. Participating in trials can also be time-consuming and may require hospital stays. However, trials are required to reimburse reasonable costs incurred, such as travel.

Any volunteer can withdraw from a trial at any time. If this happens, the care team should be advised of the reasons for withdrawing as this may influence the future recruitment of additional trial participants.

Treatments used in trials may not be made available immediately, or at all, after the end of the trial, in which case you would revert to treatments that are currently available. Even if the new treatment is effective and is brought onto the market, you should be aware that you may not be prescribed it to treat your Parkinson’s. The condition is extremely variable and new drugs are unlikely to be effective for everybody.

Consent and responsibilities

If you are accepted to join a trial, the research team running it must have your permission (consent) to enter you into the trial. You will be asked to sign a form to show you understand what is involved in taking part and that you agree to this. Before signing, the research team should talk you through in detail what is involved and answer any questions you have. It is important to note that although you will be asked to sign an informed consent document, this is not a contract and you may withdraw from the trial at any time. 

Below are just some of the responsibilities you should expect to take on when enrolling as a volunteer. You should:

  • read all the information you have been given and ask questions if anything is unclear
  • ensure that you inform study staff if your contact details change at any time
  • provide a full medical history before you start treatment and a list of any medications you take, including over-the-counter medications
  • keep a written record and report any illnesses or changes in your condition as the study progresses
  • follow instructions carefully and always talk to study staff if you think you need to make any adjustments
  • diarise any appointments you are asked to attend as these are important to the study
  • be honest with your feedback relating to the treatment or study
  • try to remain in the study until its conclusion unless there is good reason to withdraw
  • follow instructions regarding the submission of any expenses, making sure that receipts are passed on within the requested timeframe.

The trial may last for several years so it can take a long time for the results to be known. Once completed, the results will be available to all those who took part.

How do I find the right trial for me? 

There are many trials running at any one time on a range of potential Parkinson’s treatments. Some may run only in a particular country, while others may span many countries. Finding the right trial in your own country will require time and patience so don’t be put off if you don’t find a suitable trial straight away.

A good place to start is by asking your doctor or neurologist if they are aware of any trials or research centres in your area. Others you know who have participated in trials before or a local Parkinson’s support group may also have ideas to share with you.

If there is a research centre in your area, try calling the neurology department and ask to speak to someone involved in Parkinson’s trial recruitment.

The list of trials is constantly changing but the following websites may be helpful in researching current trials:

  • The EU Clinical Trials Register provides a search facility for information on clinical trials in European Union (EU) member states and the European Economic Area (EEA)
  • UK Clinical Trials Gateway lists clinical trials based in the UK
  • Parkinson's UK details current UK Parkinson’s clinical studies
  • provides a search facility for trials in over 170 countries on a wide range of conditions
  • Fox Trial Finder lists ongoing Parkinson’s trials and research studies and also matches registrants to the trials that need them and are best-suited to their specific traits
  • CenterWatch include links to search facility for patients and healthcare professionals
  • Parkinson’s Study Group: clinical trials in progress
  • database of primary clinical trials
  • UK Clinical Research Network Study Portfolio

It is a good idea to record all the trials and contacts you pursue and the responses you receive. If you enquire about a trial and you are unsuitable or they are no longer recruiting, ask the coordinator to keep in touch regarding future trials which may be more appropriate.  If you are initially unable to join a trial which interests you, don’t be discouraged from enquiring about others as new ones are regularly launched and need a broad range of participants. 

Once you have found a trial you are interested in, check the criteria for participation. If you think you are suitable, contact the trial coordinator and ask for more detailed information and raise any particular queries you have.  If you meet with the trial coordinator, it may be helpful to take someone with you so that they can take notes. 

If the trial is currently enrolling, you may be asked to attend a screening appointment before being accepted. Some medical tests may be performed to establish your fitness for the trial and so that your health before and after the treatment can be compared.

Key information to find out is outlined below.

  • What is the purpose of the trial?
  • How long is the trial expected to last?
  • What tests, if any, have been conducted so far, into the efficacy and safety of the treatment? How can I access results of previous investigations?
  • Why do researchers believe that the treatment will be as or more effective than my current treatment?
  • How many hours will my involvement take and over what period of time?
  • When will I start?
  • Will I be asked to sign any contracts?
  • What are my responsibilities as a participant?
  • How will I know if the treatment is working?
  • Is the treatment likely to make me feel unwell or uncomfortable and if so, for how long?
  • What experimental treatments or tests will be carried out?
  • Where will these be carried out, will hospital stays be required and if so how frequently and for how long?
  • Will I be expected to attend any meetings and if so how many and for how long?
  • Is the treatment likely to have an impact on my daily life and quality of life?
  • Will I be able to take other medications and/or over-the-counter treatments?
  • What are the perceived risks, benefits and possible side effects in comparison to my current treatment?
  • What long term follow up will be required?
  • Who will monitor my treatment, care and safety during the trial?
  • Will someone keep my doctor informed of progress?
  • Is there someone I can contact on the research team if I have any queries?
  • Who will pay for the treatment and will my expenses be reimbursed?
  • If my symptoms improve during the trial, will I be allowed to continue using the new treatment once the trial has ended, and before it is registered?
  • If I become unwell or develop symptoms related to the trial treatment, will I be entitled to medical care and how will this be handled?

Be prepared to keep notes in order to track changes to your symptoms, either using forms provided by the trial coordinator or your own notebook or Parkinson’s diary. Written notes are always helpful for remembering specific details when reporting back to the research team.

Terms commonly used in relation to clinical trials

Control/control group: in a trial the control is usually a group of people who receive a placebo instead of the experimental treatment. This group is used as the standard by which to evaluate findings.

Double-blind: in a double-blind trial neither the participants nor the researchers know who is receiving the active treatment and who is receiving placebo. This is in contrast to a single-blind trial where the researchers know who is in which group but the participants do not, or an open-label trial in which both participants and researchers know who is receiving the active treatment or placebo.

Eligibility criteria: guidelines to determine who is suitable and able to participate in a particular trial. A study will require that participants share certain criteria, for example gender, age, medical history, to ensure that trial results are due to the treatment under investigation and are not influenced by other factors. This allows for more accurate and meaningful results. 

Inclusion/exclusion criteria: agreed standards used to identify who is suitable for a particular study. These standards also ensure the safety of those who enrol and generally include gender, age, previous treatments received, the stage of a condition and other co-existing medical conditions. 

Informed consent: a document that details the study in very understandable terms. This usually includes the purpose and duration of the study, the proposed treatment, its potential benefits and risks, details of any studies to date, agreed procedures and key contacts. All participants must give their consent based on the information contained in this document. If unable to give consent then someone authorised to act on the volunteer’s behalf must do so. Although this document must be signed, it does not constitute a contract and volunteers can withdraw from a study at any time.

Placebo: a placebo is a pill, liquid or other form of treatment that has no active medication. It is usually used alongside an active form of the treatment or compound being trialled. Use of a placebo against the active treatment allows comparisons to be made on efficacy.

Protocol: a very detailed plan which forms the basis for the conduct of a scientific or medical experiment, treatment, or procedure. A protocol is in place for all clinical trials both to protect the participants and to answer specific research questions. Key points in a protocol include the nature of the participants, the schedule of any procedures or tests, the medications and dosages involved, and the time-span of the study. 

Screening: process for the selection of study participants based on agreed eligibility criteria (see above).

Content last reviewed: June 2015

Related reading

  • Navigating Clinical Trials - A Guide for Parkinson’s Patients and Families (The Michael J. Fox Foundation)
  • From lab to patient: how medicines are approved - video produced by the European Medicines Agency (EMA

Articles from Parkinson's Life online magazine

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