Skip to content
Clinical Trials – home

Rare diseases

Investigational molecules

Locations

Our offerNewsroom

RecruitingRare disease

Study of oral cladribine compared to placebo for patients with generalized myasthenia gravis

Fast replyRegistered drugNo placebo
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

What is this trial about?

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

This study is looking at Generalized Myasthenia Gravis, a condition where the immune system causes muscle weakness throughout the body. The study will test a medicine called cladribine in capsule form to see if it can help people with this condition. Some participants will receive cladribine at different dose levels, while others will receive placebo. The study will also use Shingrix, which is a vaccine that helps prevent shingles, a painful rash caused by the same virus that causes chickenpox.

The purpose of this study is to find out if cladribine capsules can improve symptoms of Generalized Myasthenia Gravis compared to placebo. The study will measure how well participants can perform daily activities and how strong their muscles are. It will also look at how cladribine affects quality of life for people living with this condition. The researchers want to understand if this treatment is safe and whether it causes any unwanted effects.

The study is divided into three periods and participants will be randomly assigned to receive either a high dose of cladribine, a low dose of cladribine, or placebo. During the study, participants will continue taking any other medications they were already using for their condition, such as steroids or medicines that help with muscle function. The researchers will regularly check muscle strength and the ability to do everyday tasks like talking, chewing, swallowing, and using arms and legs. Blood tests and other safety checks will be done throughout the study to monitor participants' health. If needed, some participants may receive additional treatment during the study.

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

    Initial treatment period begins

    Your participation in the study starts with the double-blind placebo controlled period, which lasts for 24 weeks. During this time, neither you nor your doctor will know whether you are receiving the active medication or a placebo.

    You will be assigned to one of three groups: high dose cladribine, low dose cladribine, or placebo. The assignment is done randomly, similar to flipping a coin.

    Cladribine is a medication given as hard capsules that you take by mouth. If you receive placebo, you will take capsules that look identical but contain no active medication.

  2. Step 2

    Continuing stable background treatment

    If you are taking corticosteroids (anti-inflammatory medications such as prednisone, prednisolone, or methylprednisolone), you will continue taking them at the same daily dose throughout the study. Your dose must remain stable and not exceed 20 milligrams per day for prednisone or prednisolone, or 16 milligrams per day for methylprednisolone.

    If you are taking acetylcholinesterase inhibitors (medications that help improve muscle strength), you will continue taking them at the same daily dose throughout the study.

  3. Step 3

    Regular assessments during the 24-week period

    Your condition will be regularly evaluated using several assessment tools. These include the MG-ADL scale, which measures how your condition affects your daily activities; the QMG scale, which measures muscle strength through specific tests; and the MGC scale, which is a combined assessment of your symptoms.

    Your quality of life will be assessed using the MG-QoL15r questionnaire, which evaluates how your condition affects your overall wellbeing.

    Blood samples will be taken to monitor your lymphocyte count (a type of white blood cell) and to measure the levels of medication in your blood if you are receiving cladribine.

    Your vital signs, such as blood pressure and heart rate, will be monitored regularly.

    Any side effects or health changes you experience will be recorded and evaluated by your doctor.

  4. Step 4

    Vaccination requirement

    You will receive the Shingrix vaccine, which protects against shingles (herpes zoster). This vaccine is given as an intramuscular injection, meaning it is injected into a muscle, typically in your upper arm.

    The vaccine comes as a powder and liquid that are mixed together before injection.

  5. Step 5

    Completion of the 24-week double-blind period

    At week 24, your response to treatment will be assessed. Your doctor will compare your current symptoms and test results to those recorded at the beginning of the study.

    A responder is defined as someone who shows meaningful improvement in their assessment scores compared to the starting point.

  6. Step 6

    Continuation and potential retreatment

    After the initial 24-week period, the study continues with additional treatment periods.

    If you initially received the full dose of cladribine and your symptoms improve, the time until you might need another course of treatment (called retreatment) will be monitored.

    If your symptoms do not improve sufficiently or worsen, you may receive rescue treatment, which means additional or alternative medication to help manage your condition.

    The total duration of your participation in the study extends beyond the initial 24 weeks, with the study estimated to continue until 2030.

  7. Step 7

    Ongoing safety monitoring

    Throughout the entire study, your safety will be closely monitored. Any adverse events (unwanted medical occurrences) will be recorded and classified by severity.

    Special attention will be given to specific types of side effects that are of particular interest based on the known effects of cladribine.

    Laboratory tests will continue to monitor your blood cell counts and other important health markers.

    The study team will track all health changes to ensure your safety throughout your participation.

Who can join the trial?

8 criteria

  • You must have a diagnosis of Generalized Myasthenia Gravis, which is a condition causing muscle weakness throughout the body, with muscle weakness classified as moderate to severe but not the most severe form
  • You must test positive for specific antibodies in your blood called Acetylcholine receptor antibodies or muscle-specific kinase antibodies, which are proteins that your immune system makes, or you may qualify if you do not have these antibodies or if you have a different type called anti-LRP4 antibodies
  • You must have a score of 6 or higher on a questionnaire called MG-ADL, which measures how much your daily activities are affected by muscle weakness, and at least half of your score must come from symptoms that are not related to your eyes
  • Your MG-ADL scores must be stable between two visits, with no more than 2 points difference, and you must not have had a worsening of your myasthenia gravis during the screening period
  • If you are taking oral corticosteroids, which are medicines that reduce inflammation and suppress the immune system, you must have been on the same daily dose for at least 3 months before joining the study, and your dose must not be more than 20 milligrams per day of prednisone or prednisolone, or 16 milligrams per day of methylprednisolone
  • If you are taking acetylcholinesterase inhibitors, which are medicines that help improve muscle strength by affecting certain chemicals in your body, you must have been on the same daily dose for at least 3 months before joining the study
  • You must weigh at least 40 kilograms, which is approximately 88 pounds
  • Other requirements as defined by the study protocol may also apply

Who cannot join the trial?

4 criteria

  • The specific exclusion criteria (reasons why you cannot join this study) have not been provided in the available information
  • Generally, clinical trials have rules about who cannot participate to ensure safety and accurate results
  • These rules may include having certain other medical conditions, taking specific medications, or having particular test results that would make the study unsafe or unsuitable for you
  • The study doctor will review all requirements with you during the screening process, which is when they check if you can safely take part in the study
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

We usually reply within a few days

Verified sites

All sites with verified contact details – recruitment status may not be available; ask directly

Trial locations

Where you can join this trial

Countries are shaded by recruitment status. Click a recruiting country to ask about joining there.

RecruitingNot recruiting
Not finding your country?

Not sure what to do next?

Joining a clinical trial can seem overwhelming. We guide you step by step, so you know exactly what to expect and how we support you through the process.

See the full process and FAQ

Investigated drugs

Cladribine is a medication that affects the immune system. In this study, it is being tested as a treatment for a condition called generalized myasthenia gravis, which causes muscle weakness. The medication comes in capsule form that you take by mouth. Researchers are testing whether cladribine can help improve muscle strength and reduce symptoms compared to a placebo (an inactive treatment with no medicine in it).

What is already known about the treatment

Cladribine – Cladribine is a medication being tested in capsule form for the treatment of Generalized Myasthenia Gravis, a condition where muscles become weak and tire easily. This study is examining whether cladribine capsules, given by mouth in different doses, can help improve symptoms compared to a placebo (inactive treatment). The medication works at the cellular level by affecting certain immune cells called lymphocytes, which are believed to play a role in attacking the body's own tissues in myasthenia gravis. Cladribine belongs to a group of medicines called immunosuppressants, which help reduce the activity of the immune system.

Investigated diseases

Generalized Myasthenia Gravis – Generalized Myasthenia Gravis is a chronic autoimmune disorder that affects the communication between nerves and muscles throughout the body. The immune system mistakenly produces antibodies that block or destroy the receptors needed for muscles to receive signals from nerves. This results in muscle weakness that typically worsens with activity and improves with rest. The condition affects various muscle groups including those controlling eye movement, facial expression, swallowing, breathing, and limb movement. Symptoms can vary in severity from person to person and may fluctuate over time. The weakness tends to progress during periods of physical activity and may affect daily activities such as lifting objects, climbing stairs, or maintaining posture.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2023-507746-83-00Protocol codeMS700568_0183Estimated enrolment266 patientsSponsorMerck Healthcare KGaA

sourced from the EU Clinical Trials Register and site verification

Want to learn more about this trial or check if you can participate?

Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

ClinicalTrials.eu

Every clinical trial in Europe, in plain language.

Explore the full ecosystem of clinical research in Europe.

Search trials

Legal notice · Published by CTIN POLAND sp. z o.o., ul. rtm. Witolda Pileckiego 67/109, 02-781 Warsaw, Poland · KRS 0001111334 · REGON 528919042 · NIP 9512598637

© 2026 Clinical Trials EU – European Clinical Trials Information Network

GDPR compliance, ISO 9001 and ISO 27001 certified (LL-C Certification)

On this site, “treatment” means an investigational medicine being studied in a clinical trial. Its safety and efficacy for the use being studied have not yet been confirmed, some participants may receive a placebo or a comparator medicine, and taking part does not guarantee any health benefit. The decision to take part is made by the doctor at the research site. This site is for information only and does not replace medical advice.

This service is not affiliated with the European Commission, the EMA, or the official CTIS system. Most information comes from publicly available international clinical-trial registries, supplemented by data from academic sites, national regulators and commercial sponsors. On this site, “treatment” and “therapy” mean a medicine being tested in a clinical trial. Its safety and effectiveness in the use being studied are not yet confirmed, some participants may receive a placebo or a comparator, and taking part does not guarantee a health benefit. The doctor at the research site decides who can take part. This site provides information, not medical advice. Certain content and visual elements on this website have been generated or enhanced using artificial intelligence (AI).