A Phase 3 Study of Fenfluramine Hydrochloride for Safety and Efficacy in Patients with Rett Syndrome

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What is this study about?

The study focuses on Rett syndrome, a rare neurological condition that usually appears in early childhood and leads to difficulties with movement, speech, and learning. The medication being tested is an oral liquid called fenfluramine hydrochloride, which is given by mouth at a dose based on body weight. A matching placebo with no active ingredient is also used for comparison.

The main goal of the trial is to find out whether the study drug is safe and can improve the symptoms of Rett syndrome. Participants are randomly assigned to receive either the medication or the placebo, and neither the participants nor the researchers know which one is being given. The treatment period lasts about three months, during which caregivers and clinicians complete questionnaires about behavior, sleep, and communication, and routine heart checks are performed. After the initial phase, participants may continue in an open‑label extension where all receive the active medication, allowing further observation of long‑term safety and benefit.

1 baseline visit and randomization

after joining the study, you attend a baseline visit where eligibility is confirmed and initial measurements are taken. assessments include the rett syndrome behaviour questionnaire, sleep disturbance questionnaire, observer‑reported communication ability questionnaire, a 12‑lead ecg, and a doppler echocardiogram.

based on the baseline data, you are randomly assigned to receive either fenfluramine hydrochloride oral solution or a matching placebo.

2 start of study medication

you begin taking the assigned study medication once daily by mouth.

the active medication is fintepla 2.2 mg/ml oral solution containing fenfluramine hydrochloride. the prescribed dose is 0.8 mg per kilogram of body weight each day. the volume of oral solution is calculated from the concentration (2.2 mg per ml) to achieve the correct dose.

if you are assigned to the placebo group, you take a matching oral solution that contains no active substance, using the same dosing schedule.

3 regular monitoring visits during the 14‑week treatment period

throughout the 14‑week core phase, you attend scheduled study visits. at each visit, safety is checked, any adverse events are recorded, and questionnaires are completed to track changes in behaviour, sleep, and communication.

the study team may perform repeat ecg and echocardiogram examinations as needed to monitor heart function.

4 week 14 evaluation

at the end of week 14, you complete the final set of questionnaires, including the rett syndrome behaviour questionnaire, sleep disturbance questionnaire, observer‑reported communication ability questionnaire, and caregiver global impression of change for seizures.

a follow‑up ecg and doppler echocardiogram are performed to assess any changes in heart rhythm or valve function.

the study team evaluates all collected data to determine the primary and secondary outcomes.

5 open‑label extension

after the week‑14 assessment, you may enter an open‑label extension in which all participants receive fenfluramine hydrochloride oral solution.

the same daily dose of 0.8 mg/kg is continued, and ongoing safety monitoring and periodic assessments are performed for as long as the extension continues.

Who Can Join the Study?

Be diagnosed with Rett Syndrome that matches the typical or classic form as defined by the RettSearch Consortium criteria.
Have a known disease‑causing change (mutation) in the MECP2 gene, which is the gene linked to Rett Syndrome.
Have been in a stable “post‑regression” phase for at least six months, meaning you have not lost or gotten worse in walking or standing, hand use, speech (including babbling or words), or non‑verbal communication such as eye contact and social attentiveness.
Score between 10 and 36 (inclusive) on the Rett Syndrome Clinical Severity Scale (RTT‑CSS), a tool doctors use to measure how severe the condition is.
Receive a rating of 4 or higher on the Clinical Global Impression‑Severity (CGI‑S) score, which reflects a moderate to severe level of illness as judged by a clinician.
Have a legal representative (such as a parent or guardian) who can sign a written informed consent form agreeing to take part in the study.
Be between 5 and 35 years old (inclusive) at the time of receiving the first study medication.
Be either male or female.
Have a regular caregiver who is at least 18 years old and can complete the study assessments, and the same caregiver should remain involved for the whole study.

Who Cannot Join the Study?

You cannot join the study if you have had cancer such as lymphoma, leukemia, or any other type in the last 5 years, except for certain skin cancers (basal cell or squamous cell) that were completely removed and have not spread for at least 3 years.
You cannot join if your doctor finds that your vital signs (like blood pressure, heart rate, temperature) are unusually abnormal and considered important for your health.
You cannot join if a heart or lung test (such as an echocardiogram (ECHO), electrocardiogram (ECG), or physical exam) shows any of the following serious problems that are not approved by the study’s central heart expert:
- More than a tiny leak in the aortic valve (aortic valve regurgitation).
- More than a mild leak in the mitral valve (mitral valve regurgitation).
- Signs of pulmonary arterial hypertension (PAH), which means high pressure in the arteries of the lungs, measured as a pulmonary artery pressure of 35 mmHg or higher.
- Weakness of the left side of the heart (left ventricular dysfunction), whether it does not pump well when the heart beats (systolic) or when it relaxes (diastolic).
- Any major heart structural problem, such as a floppy mitral valve (mitral valve prolapse), holes between the heart chambers (atrial or ventricular septal defects), or a persistent opening called a patent ductus arteriosus that allows blood to flow the wrong way (right‑to‑left shunt).
Note: A small opening called a patent foramen ovale without wrong‑way flow, or a bicuspid aortic valve, are not reasons to be excluded.
You cannot join if you have a serious medical condition that could affect the study, including:
- Chronic obstructive pulmonary disease (COPD) – a long‑term lung disease that makes breathing difficult.
- Interstitial lung disease – scarring or inflammation of lung tissue.
- Portal hypertension – high blood pressure in the vein that carries blood to the liver.
- Need for a breathing machine that goes directly into the airway (such as a tracheostomy).
- Recent (within the past 4 weeks) any illness or symptoms that could make it unsafe or hard to take part in the study.
You cannot join if you are currently taking more than four seizure medicines at the same time (rescue medicines used for emergencies do not count).

Where you can join this trial?

Verified and Recommended Sites

No sites found in this category

Verified Sites

Site Name	City	Country
Samodzielny Publiczny Zespol Zakladow Opieki Zdrowotnej W Pruszkowie	Pruszkow	Poland
Associazione Oasi Maria S.S.Onlus	Troina	Italy
Azienda Ospedaliera Universitaria Federico II Di Napoli	Naples	Italy
Centre Hospitalier Regional Et Universitaire De Brest	Brest	France
Fondazione Policlinico Universitario Agostino Gemelli IRCCS	Rome	Italy

Other Sites

Site Name	City	Country
Hospital Infantil Universitario Nino Jesus	Madrid	Spain
University Of Debrecen	Debrecen	Hungary
Magyarorszagi Reformatus Egyhaz Bethesda Gyermekkorhaza	Budapest	Hungary
Hospital Femme Mere Enfant	Bron	France
Hospital Universitario Fundacion Jimenez Diaz	Madrid	Spain
Azienda Sociosanitaria Territoriale Santi Paolo E Carlo	Milan	Italy
ASST Fatebenefratelli Sacco	Milan	Italy
IRCCS Istituto Giannina Gaslini	Genoa	Italy
Azienda Ospedaliera Universitaria Meyer IRCCS	Florence	Italy
Hospital Sant Joan De Deu Barcelona	Esplugues De Llobregat	Spain
Hopital Beaujon	Clichy	France
Centrum Medyczne Plejady Magdalena Celinska Loewenhoff Michal Zolnowski sp.k.	Cracow	Poland
Ospedale Pediatrico Bambino Gesu’	Rome	Italy
IRCCS Fondazione Stella Maris	Pisa	Italy
Hokftuir Uyadntsdhvghx Rkgsufkr Du Mjcalo	Malaga	Spain
Cxmwbwxsv Uujinmarvekiav Swccmwgrq	Woluwe-Saint-Lambert	Belgium
Sdkmly Ketszy Vaaqbuvoab Sm &rmpd Cqe Kq	Vogtareuth	Germany
Hboosork le Fl	Valencia	Spain
Hojrnsov Vqlp dppxdwhv	Barcelona	Spain
Fdkbjkpnpd Sxkzf Skgc	Sevilla	Spain
Aeoodmijfr Punycgdz Hdsrkuge Dt Mstncxrqi	Marseille	France
Uvhojskeusijzp Cuamjsn Kmdyrujmp	Gdansk	Poland
Ugeivjawmm Ow Augoyjp	Edegem	Belgium

Trial status

Country	Status	Recruitment Start
Belgium	Not yet recruiting	31.03.2026
France	Not yet recruiting	31.03.2026
Germany	Not yet recruiting	31.03.2026
Hungary	Not yet recruiting	31.03.2026
Italy	Not yet recruiting	31.03.2026
Poland	Not yet recruiting	31.03.2026
Spain	Not yet recruiting	31.03.2026

Trial locations

Investigated drugs:

Fenfluramine Hydrochloride

Fintepla 2.2 mg/ml oral solution is a liquid medicine taken by mouth that contains the active ingredient fenfluramine hydrochloride. In this trial it is being tested to see if it can help people with Rett syndrome, a condition that affects brain development and causes severe physical and cognitive challenges. The study will observe how well the medicine works to improve symptoms and will also monitor any side effects to assess its safety.

Investigated diseases:

Rett syndrome

Rett syndrome – Rett syndrome is a rare neurodevelopmental disorder that mainly affects girls. Children usually develop normally for the first six to eighteen months, after which they begin to lose previously acquired skills such as purposeful hand use and spoken language. As the condition progresses, they may experience difficulties with coordination, balance, and breathing patterns. Communication abilities often become limited, and repetitive hand movements may appear. Over time, the disorder can lead to ongoing challenges with movement and social interaction.

Trial ID:

2025-523157-34-00

Protocol code:

EP0247

Trial Phase:

Therapeutic confirmatory (Phase III)

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A Phase 3 Study of Fenfluramine Hydrochloride for Safety and Efficacy in Patients with Rett Syndrome

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?