Amsterdam UMC
Responsive
Amsterdam, The Netherlands
Not yet recruitingRare disease
Efficacy and Safety of Clemastine Fumarate in Children and Adults with Pitt‑Hopkins Syndrome: A Randomized Placebo‑Controlled Trial
Verified siteRegistered drug
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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 Pitt-Hopkins syndrome, a rare genetic condition that leads to severe developmental delays, breathing difficulties and frequent seizures. The medication being tested is clemastine, an oral tablet normally used for allergy relief, but here it is being evaluated for possible benefits in this disorder. A matching tablet that contains only microcrystalline cellulose is used as a control, so participants receiving it will not get the active drug.
The primary purpose is to determine whether clemastine produces overall improvement in daily functioning as observed by caretakers. The trial is designed so that participants are assigned by chance (randomized) to either the active drug or the control tablet (placebo), and neither the participants nor the caretakers know which one they receive.
Participants will take the assigned tablet for a defined period while attending regular visits. During these visits, caretakers will complete questionnaires about behavior, fatigue, sleep, anxiety and quality of life, and simple physical tests such as a short walking assessment may be performed. Blood samples may also be collected to study how the drug is absorbed and cleared from the body (pharmacokinetics). After the treatment phase, the collected information will be analyzed to assess safety and any potential benefits.
The research process
The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.
Who can join the trial?
5 criteria
- A diagnosis of Pitt-Hopkins syndrome that has been confirmed by a laboratory test that looks at the person’s genes.
- The child must be at least 1 year old when the study starts.
- The child must weigh at least 12 kilograms (about 26 pounds) at the start of the study.
- The parents or a legally appointed representative must be able to understand the information about what the study involves.
- The parents or legal representative must be willing to sign a written form that shows they agree to let the child take part in the study after they have been fully informed.
Who cannot join the trial?
7 criteria
- Having another disease (called comorbidity) or a second brain development disorder besides Pitt‑Hopkins syndrome that would make it hard to see how the treatment works.
- Being part of another research study at the same time unless you have approval first.
- Taking the study medicine clemastine regularly in the six months before the trial starts.
- Regularly using any medicines that are being tested in other “remyelination” studies (these are drugs that try to repair the coating of nerve cells) such as domperidone, liothyronine, quetiapine, testosterone, or bazedoxifene in the six months before the trial.
- Changing the amount or starting/stopping any psychotropic medications (drugs that affect mood, thoughts, or behavior) in the four weeks before the trial.
- Having any reason you cannot safely take clemastine (called a contraindication), such as a known condition called porphyria (a rare blood disorder) or an allergy (hypersensitivity) to clemastine or any of its inactive ingredients (excipients).
- Regularly using, or planning to keep using, medicines that calm the brain (CNS depressants) such as sleeping pills, anti‑anxiety drugs, certain antidepressants, opioid pain medicines, other antihistamines that cause sleepiness (like promethazine), or drugs that block a chemical called acetylcholine (anticholinergic medication).
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Investigated drugs
Clemastine is an oral tablet that contains the active ingredient clemastine fumarate. In this study, it is being given to children and adults who have Pitt‑Hopkins syndrome to see if it can improve their symptoms. Clemastine is a medication that is usually used for allergies, but researchers think it might also help the brain function in this condition. The trial will look at how well it works, how safe it is, and how the body processes the drug.
What is already known about the treatment
microcrystalline cellulose
This inert powder is taken orally as a tablet filler and serves as the placebo in the study, meaning it has no therapeutic effect. It is a common inactive ingredient used in many medicines and does not appear as an active drug in medical literature. Because it contains no active substance, it has no approved medical indications. Its purpose is to match the appearance of the test tablets so participants cannot tell which they receive.
Tavegyl 1 mg (clemastine fumarate)
The drug is given as an oral tablet, with a dose of 6 mg taken by mouth. Clemastine is an approved first‑generation antihistamine that is used to relieve allergy symptoms such as sneezing and itching, and it is also being studied for its potential benefit in neurological conditions like Pitt‑Hopkins syndrome. It works by blocking histamine H1 receptors, which reduces allergic reactions, and it may help nerve cells form protective coverings called myelin. Pharmacologically it belongs to the class of H1‑receptor antagonists (first‑generation antihistamines).
Investigated diseases
Pitt-Hopkins syndrome - Pitt‑Hopkins syndrome is a rare genetic disorder that affects brain development and causes intellectual disability, speech delays, and characteristic facial features. Children often show early feeding difficulties and may have distinctive breathing patterns such as brief pauses in breathing. As they grow, motor skills develop more slowly, and many experience problems with coordination and balance. Sleep disturbances and episodes of heightened anxiety are common throughout childhood. Over time, individuals may develop repetitive movements and heightened sensitivity to sensory input.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2025-524195-29-00Protocol codePTHS-clemastine-01Estimated enrolment40 patientsSponsorAmsterdam UMC Stichting
sourced from the EU Clinical Trials Register and site verification
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